Merge branch 'master' of github.com:grpc/grpc into backoff_cpp

30 files changed, 819 insertions, 738 deletions

diff --git a/.gitignore b/.gitignore
index 151bbbde13..2b35c5fb9a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -121,6 +121,7 @@ gdb.txt
 tags
 
 # perf data
+memory_usage.csv
 perf.data
 perf.data.old
 
diff --git a/src/core/ext/filters/client_channel/client_channel.cc b/src/core/ext/filters/client_channel/client_channel.cc
index 58496dc246..aced9adf9f 100644
--- a/src/core/ext/filters/client_channel/client_channel.cc
+++ b/src/core/ext/filters/client_channel/client_channel.cc
@@ -210,6 +210,14 @@ typedef struct client_channel_channel_data {
   char* info_service_config_json;
 } channel_data;
 
+typedef struct {
+  channel_data* chand;
+  /** used as an identifier, don't dereference it because the LB policy may be
+   * non-existing when the callback is run */
+  grpc_lb_policy* lb_policy;
+  grpc_closure closure;
+} reresolution_request_args;
+
 /** We create one watcher for each new lb_policy that is returned from a
     resolver, to watch for state changes from the lb_policy. When a state
     change is seen, we update the channel, and create a new watcher. */
@@ -258,21 +266,13 @@ static void set_channel_connectivity_state_locked(grpc_exec_ctx* exec_ctx,
 static void on_lb_policy_state_changed_locked(grpc_exec_ctx* exec_ctx,
                                               void* arg, grpc_error* error) {
   lb_policy_connectivity_watcher* w = (lb_policy_connectivity_watcher*)arg;
-  grpc_connectivity_state publish_state = w->state;
   /* check if the notification is for the latest policy */
   if (w->lb_policy == w->chand->lb_policy) {
     if (grpc_client_channel_trace.enabled()) {
       gpr_log(GPR_DEBUG, "chand=%p: lb_policy=%p state changed to %s", w->chand,
               w->lb_policy, grpc_connectivity_state_name(w->state));
     }
-    if (publish_state == GRPC_CHANNEL_SHUTDOWN &&
-        w->chand->resolver != nullptr) {
-      publish_state = GRPC_CHANNEL_TRANSIENT_FAILURE;
-      grpc_resolver_channel_saw_error_locked(exec_ctx, w->chand->resolver);
-      GRPC_LB_POLICY_UNREF(exec_ctx, w->chand->lb_policy, "channel");
-      w->chand->lb_policy = nullptr;
-    }
-    set_channel_connectivity_state_locked(exec_ctx, w->chand, publish_state,
+    set_channel_connectivity_state_locked(exec_ctx, w->chand, w->state,
                                           GRPC_ERROR_REF(error), "lb_changed");
     if (w->state != GRPC_CHANNEL_SHUTDOWN) {
       watch_lb_policy_locked(exec_ctx, w->chand, w->lb_policy, w->state);
@@ -369,6 +369,27 @@ static void parse_retry_throttle_params(const grpc_json* field, void* arg) {
   }
 }
 
+static void request_reresolution_locked(grpc_exec_ctx* exec_ctx, void* arg,
+                                        grpc_error* error) {
+  reresolution_request_args* args = (reresolution_request_args*)arg;
+  channel_data* chand = args->chand;
+  // If this invocation is for a stale LB policy, treat it as an LB shutdown
+  // signal.
+  if (args->lb_policy != chand->lb_policy || error != GRPC_ERROR_NONE ||
+      chand->resolver == nullptr) {
+    GRPC_CHANNEL_STACK_UNREF(exec_ctx, chand->owning_stack, "re-resolution");
+    gpr_free(args);
+    return;
+  }
+  if (grpc_client_channel_trace.enabled()) {
+    gpr_log(GPR_DEBUG, "chand=%p: started name re-resolving", chand);
+  }
+  grpc_resolver_channel_saw_error_locked(exec_ctx, chand->resolver);
+  // Give back the closure to the LB policy.
+  grpc_lb_policy_set_reresolve_closure_locked(exec_ctx, chand->lb_policy,
+                                              &args->closure);
+}
+
 static void on_resolver_result_changed_locked(grpc_exec_ctx* exec_ctx,
                                               void* arg, grpc_error* error) {
   channel_data* chand = (channel_data*)arg;
@@ -385,100 +406,114 @@ static void on_resolver_result_changed_locked(grpc_exec_ctx* exec_ctx,
   grpc_server_retry_throttle_data* retry_throttle_data = nullptr;
   grpc_slice_hash_table* method_params_table = nullptr;
   if (chand->resolver_result != nullptr) {
-    // Find LB policy name.
-    const char* lb_policy_name = nullptr;
-    const grpc_arg* channel_arg =
-        grpc_channel_args_find(chand->resolver_result, GRPC_ARG_LB_POLICY_NAME);
-    if (channel_arg != nullptr) {
-      GPR_ASSERT(channel_arg->type == GRPC_ARG_STRING);
-      lb_policy_name = channel_arg->value.string;
-    }
-    // Special case: If at least one balancer address is present, we use
-    // the grpclb policy, regardless of what the resolver actually specified.
-    channel_arg =
-        grpc_channel_args_find(chand->resolver_result, GRPC_ARG_LB_ADDRESSES);
-    if (channel_arg != nullptr && channel_arg->type == GRPC_ARG_POINTER) {
-      grpc_lb_addresses* addresses =
-          (grpc_lb_addresses*)channel_arg->value.pointer.p;
-      bool found_balancer_address = false;
-      for (size_t i = 0; i < addresses->num_addresses; ++i) {
-        if (addresses->addresses[i].is_balancer) {
-          found_balancer_address = true;
-          break;
+    if (chand->resolver != nullptr) {
+      // Find LB policy name.
+      const char* lb_policy_name = nullptr;
+      const grpc_arg* channel_arg = grpc_channel_args_find(
+          chand->resolver_result, GRPC_ARG_LB_POLICY_NAME);
+      if (channel_arg != nullptr) {
+        GPR_ASSERT(channel_arg->type == GRPC_ARG_STRING);
+        lb_policy_name = channel_arg->value.string;
+      }
+      // Special case: If at least one balancer address is present, we use
+      // the grpclb policy, regardless of what the resolver actually specified.
+      channel_arg =
+          grpc_channel_args_find(chand->resolver_result, GRPC_ARG_LB_ADDRESSES);
+      if (channel_arg != nullptr && channel_arg->type == GRPC_ARG_POINTER) {
+        grpc_lb_addresses* addresses =
+            (grpc_lb_addresses*)channel_arg->value.pointer.p;
+        bool found_balancer_address = false;
+        for (size_t i = 0; i < addresses->num_addresses; ++i) {
+          if (addresses->addresses[i].is_balancer) {
+            found_balancer_address = true;
+            break;
+          }
+        }
+        if (found_balancer_address) {
+          if (lb_policy_name != nullptr &&
+              strcmp(lb_policy_name, "grpclb") != 0) {
+            gpr_log(GPR_INFO,
+                    "resolver requested LB policy %s but provided at least one "
+                    "balancer address -- forcing use of grpclb LB policy",
+                    lb_policy_name);
+          }
+          lb_policy_name = "grpclb";
         }
       }
-      if (found_balancer_address) {
-        if (lb_policy_name != nullptr &&
-            strcmp(lb_policy_name, "grpclb") != 0) {
-          gpr_log(GPR_INFO,
-                  "resolver requested LB policy %s but provided at least one "
-                  "balancer address -- forcing use of grpclb LB policy",
+      // Use pick_first if nothing was specified and we didn't select grpclb
+      // above.
+      if (lb_policy_name == nullptr) lb_policy_name = "pick_first";
+      grpc_lb_policy_args lb_policy_args;
+      lb_policy_args.args = chand->resolver_result;
+      lb_policy_args.client_channel_factory = chand->client_channel_factory;
+      lb_policy_args.combiner = chand->combiner;
+      // Check to see if we're already using the right LB policy.
+      // Note: It's safe to use chand->info_lb_policy_name here without
+      // taking a lock on chand->info_mu, because this function is the
+      // only thing that modifies its value, and it can only be invoked
+      // once at any given time.
+      lb_policy_name_changed =
+          chand->info_lb_policy_name == nullptr ||
+          gpr_stricmp(chand->info_lb_policy_name, lb_policy_name) != 0;
+      if (chand->lb_policy != nullptr && !lb_policy_name_changed) {
+        // Continue using the same LB policy.  Update with new addresses.
+        lb_policy_updated = true;
+        grpc_lb_policy_update_locked(exec_ctx, chand->lb_policy,
+                                     &lb_policy_args);
+      } else {
+        // Instantiate new LB policy.
+        new_lb_policy =
+            grpc_lb_policy_create(exec_ctx, lb_policy_name, &lb_policy_args);
+        if (new_lb_policy == nullptr) {
+          gpr_log(GPR_ERROR, "could not create LB policy \"%s\"",
                   lb_policy_name);
+        } else {
+          reresolution_request_args* args =
+              (reresolution_request_args*)gpr_zalloc(sizeof(*args));
+          args->chand = chand;
+          args->lb_policy = new_lb_policy;
+          GRPC_CLOSURE_INIT(&args->closure, request_reresolution_locked, args,
+                            grpc_combiner_scheduler(chand->combiner));
+          GRPC_CHANNEL_STACK_REF(chand->owning_stack, "re-resolution");
+          grpc_lb_policy_set_reresolve_closure_locked(exec_ctx, new_lb_policy,
+                                                      &args->closure);
         }
-        lb_policy_name = "grpclb";
-      }
-    }
-    // Use pick_first if nothing was specified and we didn't select grpclb
-    // above.
-    if (lb_policy_name == nullptr) lb_policy_name = "pick_first";
-    grpc_lb_policy_args lb_policy_args;
-    lb_policy_args.args = chand->resolver_result;
-    lb_policy_args.client_channel_factory = chand->client_channel_factory;
-    lb_policy_args.combiner = chand->combiner;
-    // Check to see if we're already using the right LB policy.
-    // Note: It's safe to use chand->info_lb_policy_name here without
-    // taking a lock on chand->info_mu, because this function is the
-    // only thing that modifies its value, and it can only be invoked
-    // once at any given time.
-    lb_policy_name_changed =
-        chand->info_lb_policy_name == nullptr ||
-        gpr_stricmp(chand->info_lb_policy_name, lb_policy_name) != 0;
-    if (chand->lb_policy != nullptr && !lb_policy_name_changed) {
-      // Continue using the same LB policy.  Update with new addresses.
-      lb_policy_updated = true;
-      grpc_lb_policy_update_locked(exec_ctx, chand->lb_policy, &lb_policy_args);
-    } else {
-      // Instantiate new LB policy.
-      new_lb_policy =
-          grpc_lb_policy_create(exec_ctx, lb_policy_name, &lb_policy_args);
-      if (new_lb_policy == nullptr) {
-        gpr_log(GPR_ERROR, "could not create LB policy \"%s\"", lb_policy_name);
       }
-    }
-    // Find service config.
-    channel_arg =
-        grpc_channel_args_find(chand->resolver_result, GRPC_ARG_SERVICE_CONFIG);
-    if (channel_arg != nullptr) {
-      GPR_ASSERT(channel_arg->type == GRPC_ARG_STRING);
-      service_config_json = gpr_strdup(channel_arg->value.string);
-      grpc_service_config* service_config =
-          grpc_service_config_create(service_config_json);
-      if (service_config != nullptr) {
-        channel_arg =
-            grpc_channel_args_find(chand->resolver_result, GRPC_ARG_SERVER_URI);
-        GPR_ASSERT(channel_arg != nullptr);
+      // Find service config.
+      channel_arg = grpc_channel_args_find(chand->resolver_result,
+                                           GRPC_ARG_SERVICE_CONFIG);
+      if (channel_arg != nullptr) {
         GPR_ASSERT(channel_arg->type == GRPC_ARG_STRING);
-        grpc_uri* uri =
-            grpc_uri_parse(exec_ctx, channel_arg->value.string, true);
-        GPR_ASSERT(uri->path[0] != '\0');
-        service_config_parsing_state parsing_state;
-        memset(&parsing_state, 0, sizeof(parsing_state));
-        parsing_state.server_name =
-            uri->path[0] == '/' ? uri->path + 1 : uri->path;
-        grpc_service_config_parse_global_params(
-            service_config, parse_retry_throttle_params, &parsing_state);
-        grpc_uri_destroy(uri);
-        retry_throttle_data = parsing_state.retry_throttle_data;
-        method_params_table = grpc_service_config_create_method_config_table(
-            exec_ctx, service_config, method_parameters_create_from_json,
-            method_parameters_ref_wrapper, method_parameters_unref_wrapper);
-        grpc_service_config_destroy(service_config);
+        service_config_json = gpr_strdup(channel_arg->value.string);
+        grpc_service_config* service_config =
+            grpc_service_config_create(service_config_json);
+        if (service_config != nullptr) {
+          channel_arg = grpc_channel_args_find(chand->resolver_result,
+                                               GRPC_ARG_SERVER_URI);
+          GPR_ASSERT(channel_arg != nullptr);
+          GPR_ASSERT(channel_arg->type == GRPC_ARG_STRING);
+          grpc_uri* uri =
+              grpc_uri_parse(exec_ctx, channel_arg->value.string, true);
+          GPR_ASSERT(uri->path[0] != '\0');
+          service_config_parsing_state parsing_state;
+          memset(&parsing_state, 0, sizeof(parsing_state));
+          parsing_state.server_name =
+              uri->path[0] == '/' ? uri->path + 1 : uri->path;
+          grpc_service_config_parse_global_params(
+              service_config, parse_retry_throttle_params, &parsing_state);
+          grpc_uri_destroy(uri);
+          retry_throttle_data = parsing_state.retry_throttle_data;
+          method_params_table = grpc_service_config_create_method_config_table(
+              exec_ctx, service_config, method_parameters_create_from_json,
+              method_parameters_ref_wrapper, method_parameters_unref_wrapper);
+          grpc_service_config_destroy(service_config);
+        }
       }
+      // Before we clean up, save a copy of lb_policy_name, since it might
+      // be pointing to data inside chand->resolver_result.
+      // The copy will be saved in chand->lb_policy_name below.
+      lb_policy_name_dup = gpr_strdup(lb_policy_name);
     }
-    // Before we clean up, save a copy of lb_policy_name, since it might
-    // be pointing to data inside chand->resolver_result.
-    // The copy will be saved in chand->lb_policy_name below.
-    lb_policy_name_dup = gpr_strdup(lb_policy_name);
     grpc_channel_args_destroy(exec_ctx, chand->resolver_result);
     chand->resolver_result = nullptr;
   }
@@ -515,11 +550,11 @@ static void on_resolver_result_changed_locked(grpc_exec_ctx* exec_ctx,
   }
   chand->method_params_table = method_params_table;
   // If we have a new LB policy or are shutting down (in which case
-  // new_lb_policy will be NULL), swap out the LB policy, unreffing the
-  // old one and removing its fds from chand->interested_parties.
-  // Note that we do NOT do this if either (a) we updated the existing
-  // LB policy above or (b) we failed to create the new LB policy (in
-  // which case we want to continue using the most recent one we had).
+  // new_lb_policy will be NULL), swap out the LB policy, unreffing the old one
+  // and removing its fds from chand->interested_parties. Note that we do NOT do
+  // this if either (a) we updated the existing LB policy above or (b) we failed
+  // to create the new LB policy (in which case we want to continue using the
+  // most recent one we had).
   if (new_lb_policy != nullptr || error != GRPC_ERROR_NONE ||
       chand->resolver == nullptr) {
     if (chand->lb_policy != nullptr) {
diff --git a/src/core/ext/filters/client_channel/lb_policy.cc b/src/core/ext/filters/client_channel/lb_policy.cc
index 6276c3e952..db566f1b56 100644
--- a/src/core/ext/filters/client_channel/lb_policy.cc
+++ b/src/core/ext/filters/client_channel/lb_policy.cc
@@ -161,3 +161,30 @@ void grpc_lb_policy_update_locked(grpc_exec_ctx* exec_ctx,
                                   const grpc_lb_policy_args* lb_policy_args) {
   policy->vtable->update_locked(exec_ctx, policy, lb_policy_args);
 }
+
+void grpc_lb_policy_set_reresolve_closure_locked(
+    grpc_exec_ctx* exec_ctx, grpc_lb_policy* policy,
+    grpc_closure* request_reresolution) {
+  policy->vtable->set_reresolve_closure_locked(exec_ctx, policy,
+                                               request_reresolution);
+}
+
+void grpc_lb_policy_try_reresolve(grpc_exec_ctx* exec_ctx,
+                                  grpc_lb_policy* policy,
+                                  grpc_core::TraceFlag* grpc_lb_trace,
+                                  grpc_error* error) {
+  if (policy->request_reresolution != nullptr) {
+    GRPC_CLOSURE_SCHED(exec_ctx, policy->request_reresolution, error);
+    policy->request_reresolution = nullptr;
+    if (grpc_lb_trace->enabled()) {
+      gpr_log(GPR_DEBUG,
+              "%s %p: scheduling re-resolution closure with error=%s.",
+              grpc_lb_trace->name(), policy, grpc_error_string(error));
+    }
+  } else {
+    if (grpc_lb_trace->enabled() && error == GRPC_ERROR_NONE) {
+      gpr_log(GPR_DEBUG, "%s %p: re-resolution already in progress.",
+              grpc_lb_trace->name(), policy);
+    }
+  }
+}
diff --git a/src/core/ext/filters/client_channel/lb_policy.h b/src/core/ext/filters/client_channel/lb_policy.h
index 72d027995a..d3159eebf3 100644
--- a/src/core/ext/filters/client_channel/lb_policy.h
+++ b/src/core/ext/filters/client_channel/lb_policy.h
@@ -38,6 +38,8 @@ struct grpc_lb_policy {
   grpc_pollset_set* interested_parties;
   /* combiner under which lb_policy actions take place */
   grpc_combiner* combiner;
+  /* callback to force a re-resolution */
+  grpc_closure* request_reresolution;
 };
 
 /** Extra arguments for an LB pick */
@@ -96,6 +98,11 @@ struct grpc_lb_policy_vtable {
 
   void (*update_locked)(grpc_exec_ctx* exec_ctx, grpc_lb_policy* policy,
                         const grpc_lb_policy_args* args);
+
+  /** \see grpc_lb_policy_set_reresolve_closure */
+  void (*set_reresolve_closure_locked)(grpc_exec_ctx* exec_ctx,
+                                       grpc_lb_policy* policy,
+                                       grpc_closure* request_reresolution);
 };
 
 #ifndef NDEBUG
@@ -202,4 +209,16 @@ void grpc_lb_policy_update_locked(grpc_exec_ctx* exec_ctx,
                                   grpc_lb_policy* policy,
                                   const grpc_lb_policy_args* lb_policy_args);
 
+/** Set the re-resolution closure to \a request_reresolution. */
+void grpc_lb_policy_set_reresolve_closure_locked(
+    grpc_exec_ctx* exec_ctx, grpc_lb_policy* policy,
+    grpc_closure* request_reresolution);
+
+/** Try to request a re-resolution. It's NOT a public API; it's only for use by
+    the LB policy implementations. */
+void grpc_lb_policy_try_reresolve(grpc_exec_ctx* exec_ctx,
+                                  grpc_lb_policy* policy,
+                                  grpc_core::TraceFlag* grpc_lb_trace,
+                                  grpc_error* error);
+
 #endif /* GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_LB_POLICY_H */
diff --git a/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc b/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc
index 7e5e1532e2..d8137636b8 100644
--- a/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc
+++ b/src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc
@@ -637,7 +637,7 @@ static void update_lb_connectivity_status_locked(
 
 /* Perform a pick over \a glb_policy->rr_policy. Given that a pick can return
  * immediately (ignoring its completion callback), we need to perform the
- * cleanups this callback would otherwise be resposible for.
+ * cleanups this callback would otherwise be responsible for.
  * If \a force_async is true, then we will manually schedule the
  * completion callback even if the pick is available immediately. */
 static bool pick_from_internal_rr_locked(
@@ -766,6 +766,9 @@ static void create_rr_locked(grpc_exec_ctx* exec_ctx, glb_lb_policy* glb_policy,
             glb_policy->rr_policy);
     return;
   }
+  grpc_lb_policy_set_reresolve_closure_locked(
+      exec_ctx, new_rr_policy, glb_policy->base.request_reresolution);
+  glb_policy->base.request_reresolution = nullptr;
   glb_policy->rr_policy = new_rr_policy;
   grpc_error* rr_state_error = nullptr;
   const grpc_connectivity_state rr_state =
@@ -991,6 +994,7 @@ static void glb_destroy(grpc_exec_ctx* exec_ctx, grpc_lb_policy* pol) {
 
 static void glb_shutdown_locked(grpc_exec_ctx* exec_ctx, grpc_lb_policy* pol) {
   glb_lb_policy* glb_policy = (glb_lb_policy*)pol;
+  grpc_error* error = GRPC_ERROR_CREATE_FROM_STATIC_STRING("Channel shutdown");
   glb_policy->shutting_down = true;
 
   /* We need a copy of the lb_call pointer because we can't cancell the call
@@ -1021,6 +1025,9 @@ static void glb_shutdown_locked(grpc_exec_ctx* exec_ctx, grpc_lb_policy* pol) {
   glb_policy->pending_pings = nullptr;
   if (glb_policy->rr_policy != nullptr) {
     GRPC_LB_POLICY_UNREF(exec_ctx, glb_policy->rr_policy, "glb_shutdown");
+  } else {
+    grpc_lb_policy_try_reresolve(exec_ctx, pol, &grpc_lb_glb_trace,
+                                 GRPC_ERROR_CANCELLED);
   }
   // We destroy the LB channel here because
   // glb_lb_channel_on_connectivity_changed_cb needs a valid glb_policy
@@ -1030,28 +1037,27 @@ static void glb_shutdown_locked(grpc_exec_ctx* exec_ctx, grpc_lb_policy* pol) {
     grpc_channel_destroy(glb_policy->lb_channel);
     glb_policy->lb_channel = nullptr;
   }
-  grpc_connectivity_state_set(
-      exec_ctx, &glb_policy->state_tracker, GRPC_CHANNEL_SHUTDOWN,
-      GRPC_ERROR_CREATE_FROM_STATIC_STRING("Channel Shutdown"), "glb_shutdown");
+  grpc_connectivity_state_set(exec_ctx, &glb_policy->state_tracker,
+                              GRPC_CHANNEL_SHUTDOWN, GRPC_ERROR_REF(error),
+                              "glb_shutdown");
 
   while (pp != nullptr) {
     pending_pick* next = pp->next;
     *pp->target = nullptr;
-    GRPC_CLOSURE_SCHED(
-        exec_ctx, &pp->wrapped_on_complete_arg.wrapper_closure,
-        GRPC_ERROR_CREATE_FROM_STATIC_STRING("Channel Shutdown"));
+    GRPC_CLOSURE_SCHED(exec_ctx, &pp->wrapped_on_complete_arg.wrapper_closure,
+                       GRPC_ERROR_REF(error));
     gpr_free(pp);
     pp = next;
   }
 
   while (pping != nullptr) {
     pending_ping* next = pping->next;
-    GRPC_CLOSURE_SCHED(
-        exec_ctx, &pping->wrapped_notify_arg.wrapper_closure,
-        GRPC_ERROR_CREATE_FROM_STATIC_STRING("Channel Shutdown"));
+    GRPC_CLOSURE_SCHED(exec_ctx, &pping->wrapped_notify_arg.wrapper_closure,
+                       GRPC_ERROR_REF(error));
     gpr_free(pping);
     pping = next;
   }
+  GRPC_ERROR_UNREF(error);
 }
 
 // Cancel a specific pending pick.
@@ -1754,8 +1760,8 @@ static void fallback_update_locked(grpc_exec_ctx* exec_ctx,
   grpc_lb_addresses_destroy(exec_ctx, glb_policy->fallback_backend_addresses);
   glb_policy->fallback_backend_addresses =
       extract_backend_addresses_locked(exec_ctx, addresses);
-  if (glb_policy->started_picking && glb_policy->lb_fallback_timeout_ms > 0 &&
-      !glb_policy->fallback_timer_active) {
+  if (glb_policy->lb_fallback_timeout_ms > 0 &&
+      glb_policy->rr_policy != nullptr) {
     rr_handover_locked(exec_ctx, glb_policy);
   }
 }
@@ -1853,7 +1859,7 @@ static void glb_lb_channel_on_connectivity_changed_cb(grpc_exec_ctx* exec_ctx,
         grpc_call_cancel(glb_policy->lb_call, nullptr);
         // lb_on_server_status_received() will pick up the cancel and reinit
         // lb_call.
-      } else if (glb_policy->started_picking && !glb_policy->shutting_down) {
+      } else if (glb_policy->started_picking) {
         if (glb_policy->retry_timer_active) {
           grpc_timer_cancel(exec_ctx, &glb_policy->lb_call_retry_timer);
           glb_policy->retry_timer_active = false;
@@ -1870,6 +1876,20 @@ static void glb_lb_channel_on_connectivity_changed_cb(grpc_exec_ctx* exec_ctx,
   }
 }
 
+static void glb_set_reresolve_closure_locked(
+    grpc_exec_ctx* exec_ctx, grpc_lb_policy* policy,
+    grpc_closure* request_reresolution) {
+  glb_lb_policy* glb_policy = (glb_lb_policy*)policy;
+  GPR_ASSERT(!glb_policy->shutting_down);
+  GPR_ASSERT(glb_policy->base.request_reresolution == nullptr);
+  if (glb_policy->rr_policy != nullptr) {
+    grpc_lb_policy_set_reresolve_closure_locked(exec_ctx, glb_policy->rr_policy,
+                                                request_reresolution);
+  } else {
+    glb_policy->base.request_reresolution = request_reresolution;
+  }
+}
+
 /* Code wiring the policy with the rest of the core */
 static const grpc_lb_policy_vtable glb_lb_policy_vtable = {
     glb_destroy,
@@ -1881,7 +1901,8 @@ static const grpc_lb_policy_vtable glb_lb_policy_vtable = {
     glb_exit_idle_locked,
     glb_check_connectivity_locked,
     glb_notify_on_state_change_locked,
-    glb_update_locked};
+    glb_update_locked,
+    glb_set_reresolve_closure_locked};
 
 static grpc_lb_policy* glb_create(grpc_exec_ctx* exec_ctx,
                                   grpc_lb_policy_factory* factory,
diff --git a/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc b/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc
index 6cfc37e9d1..228a77d9db 100644
--- a/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc
+++ b/src/core/ext/filters/client_channel/lb_policy/pick_first/pick_first.cc
@@ -70,8 +70,9 @@ static void pf_destroy(grpc_exec_ctx* exec_ctx, grpc_lb_policy* pol) {
   }
 }
 
-static void shutdown_locked(grpc_exec_ctx* exec_ctx, pick_first_lb_policy* p,
-                            grpc_error* error) {
+static void pf_shutdown_locked(grpc_exec_ctx* exec_ctx, grpc_lb_policy* pol) {
+  pick_first_lb_policy* p = (pick_first_lb_policy*)pol;
+  grpc_error* error = GRPC_ERROR_CREATE_FROM_STATIC_STRING("Channel shutdown");
   if (grpc_lb_pick_first_trace.enabled()) {
     gpr_log(GPR_DEBUG, "Pick First %p Shutting down", p);
   }
@@ -96,14 +97,11 @@ static void shutdown_locked(grpc_exec_ctx* exec_ctx, pick_first_lb_policy* p,
         exec_ctx, p->latest_pending_subchannel_list, "pf_shutdown");
     p->latest_pending_subchannel_list = nullptr;
   }
+  grpc_lb_policy_try_reresolve(exec_ctx, &p->base, &grpc_lb_pick_first_trace,
+                               GRPC_ERROR_CANCELLED);
   GRPC_ERROR_UNREF(error);
 }
 
-static void pf_shutdown_locked(grpc_exec_ctx* exec_ctx, grpc_lb_policy* pol) {
-  shutdown_locked(exec_ctx, (pick_first_lb_policy*)pol,
-                  GRPC_ERROR_CREATE_FROM_STATIC_STRING("Channel shutdown"));
-}
-
 static void pf_cancel_pick_locked(grpc_exec_ctx* exec_ctx, grpc_lb_policy* pol,
                                   grpc_connected_subchannel** target,
                                   grpc_error* error) {
@@ -157,10 +155,15 @@ static void start_picking_locked(grpc_exec_ctx* exec_ctx,
   if (p->subchannel_list != nullptr &&
       p->subchannel_list->num_subchannels > 0) {
     p->subchannel_list->checking_subchannel = 0;
-    grpc_lb_subchannel_list_ref_for_connectivity_watch(
-        p->subchannel_list, "connectivity_watch+start_picking");
-    grpc_lb_subchannel_data_start_connectivity_watch(
-        exec_ctx, &p->subchannel_list->subchannels[0]);
+    for (size_t i = 0; i < p->subchannel_list->num_subchannels; ++i) {
+      if (p->subchannel_list->subchannels[i].subchannel != nullptr) {
+        grpc_lb_subchannel_list_ref_for_connectivity_watch(
+            p->subchannel_list, "connectivity_watch+start_picking");
+        grpc_lb_subchannel_data_start_connectivity_watch(
+            exec_ctx, &p->subchannel_list->subchannels[i]);
+        break;
+      }
+    }
   }
 }
 
@@ -404,6 +407,9 @@ static void pf_connectivity_changed_locked(grpc_exec_ctx* exec_ctx, void* arg,
     if (sd->curr_connectivity_state != GRPC_CHANNEL_READY &&
         p->latest_pending_subchannel_list != nullptr) {
       p->selected = nullptr;
+      grpc_lb_subchannel_data_stop_connectivity_watch(exec_ctx, sd);
+      grpc_lb_subchannel_list_unref_for_connectivity_watch(
+          exec_ctx, sd->subchannel_list, "selected_not_ready+switch_to_update");
       grpc_lb_subchannel_list_shutdown_and_unref(
           exec_ctx, p->subchannel_list, "selected_not_ready+switch_to_update");
       p->subchannel_list = p->latest_pending_subchannel_list;
@@ -412,21 +418,35 @@ static void pf_connectivity_changed_locked(grpc_exec_ctx* exec_ctx, void* arg,
           exec_ctx, &p->state_tracker, GRPC_CHANNEL_TRANSIENT_FAILURE,
           GRPC_ERROR_REF(error), "selected_not_ready+switch_to_update");
     } else {
-      if (sd->curr_connectivity_state == GRPC_CHANNEL_TRANSIENT_FAILURE) {
-        /* if the selected channel goes bad, we're done */
-        sd->curr_connectivity_state = GRPC_CHANNEL_SHUTDOWN;
+      // TODO(juanlishen): we re-resolve when the selected subchannel goes to
+      // TRANSIENT_FAILURE because we used to shut down in this case before
+      // re-resolution is introduced. But we need to investigate whether we
+      // really want to take any action instead of waiting for the selected
+      // subchannel reconnecting.
+      if (sd->curr_connectivity_state == GRPC_CHANNEL_SHUTDOWN ||
+          sd->curr_connectivity_state == GRPC_CHANNEL_TRANSIENT_FAILURE) {
+        // If the selected channel goes bad, request a re-resolution.
+        grpc_connectivity_state_set(exec_ctx, &p->state_tracker,
+                                    GRPC_CHANNEL_IDLE, GRPC_ERROR_NONE,
+                                    "selected_changed+reresolve");
+        p->started_picking = false;
+        grpc_lb_policy_try_reresolve(
+            exec_ctx, &p->base, &grpc_lb_pick_first_trace, GRPC_ERROR_NONE);
+      } else {
+        grpc_connectivity_state_set(exec_ctx, &p->state_tracker,
+                                    sd->curr_connectivity_state,
+                                    GRPC_ERROR_REF(error), "selected_changed");
       }
-      grpc_connectivity_state_set(exec_ctx, &p->state_tracker,
-                                  sd->curr_connectivity_state,
-                                  GRPC_ERROR_REF(error), "selected_changed");
       if (sd->curr_connectivity_state != GRPC_CHANNEL_SHUTDOWN) {
         // Renew notification.
         grpc_lb_subchannel_data_start_connectivity_watch(exec_ctx, sd);
       } else {
+        p->selected = nullptr;
         grpc_lb_subchannel_data_stop_connectivity_watch(exec_ctx, sd);
         grpc_lb_subchannel_list_unref_for_connectivity_watch(
             exec_ctx, sd->subchannel_list, "pf_selected_shutdown");
-        shutdown_locked(exec_ctx, p, GRPC_ERROR_REF(error));
+        grpc_lb_subchannel_data_unref_subchannel(exec_ctx, sd,
+                                                 "pf_selected_shutdown");
       }
     }
     return;
@@ -531,24 +551,37 @@ static void pf_connectivity_changed_locked(grpc_exec_ctx* exec_ctx, void* arg,
       } while (sd->subchannel == nullptr && sd != original_sd);
       if (sd == original_sd) {
         grpc_lb_subchannel_list_unref_for_connectivity_watch(
-            exec_ctx, sd->subchannel_list, "pf_candidate_shutdown");
-        shutdown_locked(exec_ctx, p,
-                        GRPC_ERROR_CREATE_REFERENCING_FROM_STATIC_STRING(
-                            "Pick first exhausted channels", &error, 1));
-        break;
-      }
-      if (sd->subchannel_list == p->subchannel_list) {
-        grpc_connectivity_state_set(exec_ctx, &p->state_tracker,
-                                    GRPC_CHANNEL_TRANSIENT_FAILURE,
-                                    GRPC_ERROR_REF(error), "subchannel_failed");
+            exec_ctx, sd->subchannel_list, "pf_exhausted_subchannels");
+        if (sd->subchannel_list == p->subchannel_list) {
+          grpc_connectivity_state_set(exec_ctx, &p->state_tracker,
+                                      GRPC_CHANNEL_IDLE, GRPC_ERROR_NONE,
+                                      "exhausted_subchannels+reresolve");
+          p->started_picking = false;
+          grpc_lb_policy_try_reresolve(
+              exec_ctx, &p->base, &grpc_lb_pick_first_trace, GRPC_ERROR_NONE);
+        }
+      } else {
+        if (sd->subchannel_list == p->subchannel_list) {
+          grpc_connectivity_state_set(
+              exec_ctx, &p->state_tracker, GRPC_CHANNEL_TRANSIENT_FAILURE,
+              GRPC_ERROR_REF(error), "subchannel_failed");
+        }
+        // Reuses the connectivity refs from the previous watch.
+        grpc_lb_subchannel_data_start_connectivity_watch(exec_ctx, sd);
       }
-      // Reuses the connectivity refs from the previous watch.
-      grpc_lb_subchannel_data_start_connectivity_watch(exec_ctx, sd);
-      break;
     }
   }
 }
 
+static void pf_set_reresolve_closure_locked(
+    grpc_exec_ctx* exec_ctx, grpc_lb_policy* policy,
+    grpc_closure* request_reresolution) {
+  pick_first_lb_policy* p = (pick_first_lb_policy*)policy;
+  GPR_ASSERT(!p->shutdown);
+  GPR_ASSERT(policy->request_reresolution == nullptr);
+  policy->request_reresolution = request_reresolution;
+}
+
 static const grpc_lb_policy_vtable pick_first_lb_policy_vtable = {
     pf_destroy,
     pf_shutdown_locked,
@@ -559,7 +592,8 @@ static const grpc_lb_policy_vtable pick_first_lb_policy_vtable = {
     pf_exit_idle_locked,
     pf_check_connectivity_locked,
     pf_notify_on_state_change_locked,
-    pf_update_locked};
+    pf_update_locked,
+    pf_set_reresolve_closure_locked};
 
 static void pick_first_factory_ref(grpc_lb_policy_factory* factory) {}
 
diff --git a/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc b/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc
index 23a4cc4a5a..f68daba474 100644
--- a/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc
+++ b/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.cc
@@ -20,9 +20,9 @@
  *
  * Before every pick, the \a get_next_ready_subchannel_index_locked function
  * returns the p->subchannel_list->subchannels index for next subchannel,
- * respecting the relative
- * order of the addresses provided upon creation or updates. Note however that
- * updates will start picking from the beginning of the updated list. */
+ * respecting the relative order of the addresses provided upon creation or
+ * updates. Note however that updates will start picking from the beginning of
+ * the updated list. */
 
 #include <string.h>
 
@@ -167,8 +167,9 @@ static void rr_destroy(grpc_exec_ctx* exec_ctx, grpc_lb_policy* pol) {
   gpr_free(p);
 }
 
-static void shutdown_locked(grpc_exec_ctx* exec_ctx, round_robin_lb_policy* p,
-                            grpc_error* error) {
+static void rr_shutdown_locked(grpc_exec_ctx* exec_ctx, grpc_lb_policy* pol) {
+  round_robin_lb_policy* p = (round_robin_lb_policy*)pol;
+  grpc_error* error = GRPC_ERROR_CREATE_FROM_STATIC_STRING("Channel shutdown");
   if (grpc_lb_round_robin_trace.enabled()) {
     gpr_log(GPR_DEBUG, "[RR %p] Shutting down", p);
   }
@@ -194,15 +195,11 @@ static void shutdown_locked(grpc_exec_ctx* exec_ctx, round_robin_lb_policy* p,
         "sl_shutdown_pending_rr_shutdown");
     p->latest_pending_subchannel_list = nullptr;
   }
+  grpc_lb_policy_try_reresolve(exec_ctx, &p->base, &grpc_lb_round_robin_trace,
+                               GRPC_ERROR_CANCELLED);
   GRPC_ERROR_UNREF(error);
 }
 
-static void rr_shutdown_locked(grpc_exec_ctx* exec_ctx, grpc_lb_policy* pol) {
-  round_robin_lb_policy* p = (round_robin_lb_policy*)pol;
-  shutdown_locked(exec_ctx, p,
-                  GRPC_ERROR_CREATE_FROM_STATIC_STRING("Channel Shutdown"));
-}
-
 static void rr_cancel_pick_locked(grpc_exec_ctx* exec_ctx, grpc_lb_policy* pol,
                                   grpc_connected_subchannel** target,
                                   grpc_error* error) {
@@ -255,10 +252,12 @@ static void start_picking_locked(grpc_exec_ctx* exec_ctx,
                                  round_robin_lb_policy* p) {
   p->started_picking = true;
   for (size_t i = 0; i < p->subchannel_list->num_subchannels; i++) {
-    grpc_lb_subchannel_list_ref_for_connectivity_watch(p->subchannel_list,
-                                                       "connectivity_watch");
-    grpc_lb_subchannel_data_start_connectivity_watch(
-        exec_ctx, &p->subchannel_list->subchannels[i]);
+    if (p->subchannel_list->subchannels[i].subchannel != nullptr) {
+      grpc_lb_subchannel_list_ref_for_connectivity_watch(p->subchannel_list,
+                                                         "connectivity_watch");
+      grpc_lb_subchannel_data_start_connectivity_watch(
+          exec_ctx, &p->subchannel_list->subchannels[i]);
+    }
   }
 }
 
@@ -346,71 +345,71 @@ static void update_state_counters_locked(grpc_lb_subchannel_data* sd) {
 }
 
 /** Sets the policy's connectivity status based on that of the passed-in \a sd
- * (the grpc_lb_subchannel_data associted with the updated subchannel) and the
- * subchannel list \a sd belongs to (sd->subchannel_list). \a error will only be
- * used upon policy transition to TRANSIENT_FAILURE or SHUTDOWN. Returns the
- * connectivity status set. */
-static grpc_connectivity_state update_lb_connectivity_status_locked(
-    grpc_exec_ctx* exec_ctx, grpc_lb_subchannel_data* sd, grpc_error* error) {
+ * (the grpc_lb_subchannel_data associated with the updated subchannel) and the
+ * subchannel list \a sd belongs to (sd->subchannel_list). \a error will be used
+ * only if the policy transitions to state TRANSIENT_FAILURE. */
+static void update_lb_connectivity_status_locked(grpc_exec_ctx* exec_ctx,
+                                                 grpc_lb_subchannel_data* sd,
+                                                 grpc_error* error) {
   /* In priority order. The first rule to match terminates the search (ie, if we
    * are on rule n, all previous rules were unfulfilled).
    *
    * 1) RULE: ANY subchannel is READY => policy is READY.
-   *    CHECK: At least one subchannel is ready iff p->ready_list is NOT empty.
+   *    CHECK: subchannel_list->num_ready > 0.
    *
    * 2) RULE: ANY subchannel is CONNECTING => policy is CONNECTING.
    *    CHECK: sd->curr_connectivity_state == CONNECTING.
    *
-   * 3) RULE: ALL subchannels are SHUTDOWN => policy is SHUTDOWN.
-   *    CHECK: p->subchannel_list->num_shutdown ==
-   *           p->subchannel_list->num_subchannels.
+   * 3) RULE: ALL subchannels are SHUTDOWN => policy is IDLE (and requests
+   *          re-resolution).
+   *    CHECK: subchannel_list->num_shutdown ==
+   *           subchannel_list->num_subchannels.
    *
    * 4) RULE: ALL subchannels are TRANSIENT_FAILURE => policy is
-   *    TRANSIENT_FAILURE.
-   *    CHECK: p->num_transient_failures == p->subchannel_list->num_subchannels.
+   *          TRANSIENT_FAILURE.
+   *    CHECK: subchannel_list->num_transient_failures ==
+   *           subchannel_list->num_subchannels.
    *
    * 5) RULE: ALL subchannels are IDLE => policy is IDLE.
-   *    CHECK: p->num_idle == p->subchannel_list->num_subchannels.
+   *    CHECK: subchannel_list->num_idle == subchannel_list->num_subchannels.
+   *    (Note that all the subchannels will transition from IDLE to CONNECTING
+   *    in batch when we start trying to connect.)
    */
-  grpc_connectivity_state new_state = sd->curr_connectivity_state;
+  // TODO(juanlishen): if the subchannel states are mixed by {SHUTDOWN,
+  // TRANSIENT_FAILURE}, we don't change the state. We may want to improve on
+  // this.
   grpc_lb_subchannel_list* subchannel_list = sd->subchannel_list;
   round_robin_lb_policy* p = (round_robin_lb_policy*)subchannel_list->policy;
-  if (subchannel_list->num_ready > 0) { /* 1) READY */
+  if (subchannel_list->num_ready > 0) {
+    /* 1) READY */
     grpc_connectivity_state_set(exec_ctx, &p->state_tracker, GRPC_CHANNEL_READY,
                                 GRPC_ERROR_NONE, "rr_ready");
-    new_state = GRPC_CHANNEL_READY;
-  } else if (sd->curr_connectivity_state ==
-             GRPC_CHANNEL_CONNECTING) { /* 2) CONNECTING */
+  } else if (sd->curr_connectivity_state == GRPC_CHANNEL_CONNECTING) {
+    /* 2) CONNECTING */
     grpc_connectivity_state_set(exec_ctx, &p->state_tracker,
                                 GRPC_CHANNEL_CONNECTING, GRPC_ERROR_NONE,
                                 "rr_connecting");
-    new_state = GRPC_CHANNEL_CONNECTING;
-  } else if (p->subchannel_list->num_shutdown ==
-             p->subchannel_list->num_subchannels) { /* 3) SHUTDOWN */
-    grpc_connectivity_state_set(exec_ctx, &p->state_tracker,
-                                GRPC_CHANNEL_SHUTDOWN, GRPC_ERROR_REF(error),
-                                "rr_shutdown");
-    p->shutdown = true;
-    new_state = GRPC_CHANNEL_SHUTDOWN;
-    if (grpc_lb_round_robin_trace.enabled()) {
-      gpr_log(GPR_INFO,
-              "[RR %p] Shutting down: all subchannels have gone into shutdown",
-              (void*)p);
-    }
+  } else if (subchannel_list->num_shutdown ==
+             subchannel_list->num_subchannels) {
+    /* 3) IDLE and re-resolve */
+    grpc_connectivity_state_set(exec_ctx, &p->state_tracker, GRPC_CHANNEL_IDLE,
+                                GRPC_ERROR_NONE,
+                                "rr_exhausted_subchannels+reresolve");
+    p->started_picking = false;
+    grpc_lb_policy_try_reresolve(exec_ctx, &p->base, &grpc_lb_round_robin_trace,
+                                 GRPC_ERROR_NONE);
   } else if (subchannel_list->num_transient_failures ==
-             p->subchannel_list->num_subchannels) { /* 4) TRANSIENT_FAILURE */
+             subchannel_list->num_subchannels) {
+    /* 4) TRANSIENT_FAILURE */
     grpc_connectivity_state_set(exec_ctx, &p->state_tracker,
                                 GRPC_CHANNEL_TRANSIENT_FAILURE,
                                 GRPC_ERROR_REF(error), "rr_transient_failure");
-    new_state = GRPC_CHANNEL_TRANSIENT_FAILURE;
-  } else if (subchannel_list->num_idle ==
-             p->subchannel_list->num_subchannels) { /* 5) IDLE */
+  } else if (subchannel_list->num_idle == subchannel_list->num_subchannels) {
+    /* 5) IDLE */
     grpc_connectivity_state_set(exec_ctx, &p->state_tracker, GRPC_CHANNEL_IDLE,
                                 GRPC_ERROR_NONE, "rr_idle");
-    new_state = GRPC_CHANNEL_IDLE;
   }
   GRPC_ERROR_UNREF(error);
-  return new_state;
 }
 
 static void rr_connectivity_changed_locked(grpc_exec_ctx* exec_ctx, void* arg,
@@ -454,21 +453,16 @@ static void rr_connectivity_changed_locked(grpc_exec_ctx* exec_ctx, void* arg,
   // state (which was set by the connectivity state watcher) to
   // curr_connectivity_state, which is what we use inside of the combiner.
   sd->curr_connectivity_state = sd->pending_connectivity_state_unsafe;
-  // Update state counters and determine new overall state.
+  // Update state counters and new overall state.
   update_state_counters_locked(sd);
-  const grpc_connectivity_state new_policy_connectivity_state =
-      update_lb_connectivity_status_locked(exec_ctx, sd, GRPC_ERROR_REF(error));
-  // If the sd's new state is SHUTDOWN, unref the subchannel, and if the new
-  // policy's state is SHUTDOWN, clean up.
+  update_lb_connectivity_status_locked(exec_ctx, sd, GRPC_ERROR_REF(error));
+  // If the sd's new state is SHUTDOWN, unref the subchannel.
   if (sd->curr_connectivity_state == GRPC_CHANNEL_SHUTDOWN) {
     grpc_lb_subchannel_data_stop_connectivity_watch(exec_ctx, sd);
     grpc_lb_subchannel_data_unref_subchannel(exec_ctx, sd,
                                              "rr_connectivity_shutdown");
     grpc_lb_subchannel_list_unref_for_connectivity_watch(
         exec_ctx, sd->subchannel_list, "rr_connectivity_shutdown");
-    if (new_policy_connectivity_state == GRPC_CHANNEL_SHUTDOWN) {
-      shutdown_locked(exec_ctx, p, GRPC_ERROR_REF(error));
-    }
   } else {  // sd not in SHUTDOWN
     if (sd->curr_connectivity_state == GRPC_CHANNEL_READY) {
       if (sd->connected_subchannel == nullptr) {
@@ -504,7 +498,7 @@ static void rr_connectivity_changed_locked(grpc_exec_ctx* exec_ctx, void* arg,
       }
       /* at this point we know there's at least one suitable subchannel. Go
        * ahead and pick one and notify the pending suitors in
-       * p->pending_picks. This preemtively replicates rr_pick()'s actions. */
+       * p->pending_picks. This preemptively replicates rr_pick()'s actions. */
       const size_t next_ready_index = get_next_ready_subchannel_index_locked(p);
       GPR_ASSERT(next_ready_index < p->subchannel_list->num_subchannels);
       grpc_lb_subchannel_data* selected =
@@ -642,6 +636,15 @@ static void rr_update_locked(grpc_exec_ctx* exec_ctx, grpc_lb_policy* policy,
   }
 }
 
+static void rr_set_reresolve_closure_locked(
+    grpc_exec_ctx* exec_ctx, grpc_lb_policy* policy,
+    grpc_closure* request_reresolution) {
+  round_robin_lb_policy* p = (round_robin_lb_policy*)policy;
+  GPR_ASSERT(!p->shutdown);
+  GPR_ASSERT(policy->request_reresolution == nullptr);
+  policy->request_reresolution = request_reresolution;
+}
+
 static const grpc_lb_policy_vtable round_robin_lb_policy_vtable = {
     rr_destroy,
     rr_shutdown_locked,
@@ -652,7 +655,8 @@ static const grpc_lb_policy_vtable round_robin_lb_policy_vtable = {
     rr_exit_idle_locked,
     rr_check_connectivity_locked,
     rr_notify_on_state_change_locked,
-    rr_update_locked};
+    rr_update_locked,
+    rr_set_reresolve_closure_locked};
 
 static void round_robin_factory_ref(grpc_lb_policy_factory* factory) {}
 
diff --git a/src/core/ext/transport/chttp2/client/chttp2_connector.cc b/src/core/ext/transport/chttp2/client/chttp2_connector.cc
index 7b2bb7d2be..819f66aec3 100644
--- a/src/core/ext/transport/chttp2/client/chttp2_connector.cc
+++ b/src/core/ext/transport/chttp2/client/chttp2_connector.cc
@@ -165,8 +165,9 @@ static void start_handshake_locked(grpc_exec_ctx* exec_ctx,
   grpc_endpoint_add_to_pollset_set(exec_ctx, c->endpoint,
                                    c->args.interested_parties);
   grpc_handshake_manager_do_handshake(
-      exec_ctx, c->handshake_mgr, c->endpoint, c->args.channel_args,
-      c->args.deadline, nullptr /* acceptor */, on_handshake_done, c);
+      exec_ctx, c->handshake_mgr, c->args.interested_parties, c->endpoint,
+      c->args.channel_args, c->args.deadline, nullptr /* acceptor */,
+      on_handshake_done, c);
   c->endpoint = nullptr;  // Endpoint handed off to handshake manager.
 }
 
diff --git a/src/core/ext/transport/chttp2/server/chttp2_server.cc b/src/core/ext/transport/chttp2/server/chttp2_server.cc
index 1f4517ac28..49ee677464 100644
--- a/src/core/ext/transport/chttp2/server/chttp2_server.cc
+++ b/src/core/ext/transport/chttp2/server/chttp2_server.cc
@@ -197,9 +197,10 @@ static void on_accept(grpc_exec_ctx* exec_ctx, void* arg, grpc_endpoint* tcp,
       grpc_channel_arg_get_integer(timeout_arg,
                                    {120 * GPR_MS_PER_SEC, 1, INT_MAX});
   grpc_handshake_manager_do_handshake(exec_ctx, connection_state->handshake_mgr,
-                                      tcp, state->args,
-                                      connection_state->deadline, acceptor,
-                                      on_handshake_done, connection_state);
+                                      nullptr /* interested_parties */, tcp,
+                                      state->args, connection_state->deadline,
+                                      acceptor, on_handshake_done,
+                                      connection_state);
 }
 
 /* Server callback: start listening on our ports */
diff --git a/src/core/ext/transport/inproc/inproc_transport.cc b/src/core/ext/transport/inproc/inproc_transport.cc
index 2579060811..d8d753e459 100644
--- a/src/core/ext/transport/inproc/inproc_transport.cc
+++ b/src/core/ext/transport/inproc/inproc_transport.cc
@@ -458,6 +458,14 @@ static void fail_helper_locked(grpc_exec_ctx* exec_ctx, inproc_stream* s,
     } else {
       err = GRPC_ERROR_REF(error);
     }
+    if (s->recv_initial_md_op->payload->recv_initial_metadata
+            .trailing_metadata_available != nullptr) {
+      // Set to true unconditionally, because we're failing the call, so even
+      // if we haven't actually seen the send_trailing_metadata op from the
+      // other side, we're going to return trailing metadata anyway.
+      *s->recv_initial_md_op->payload->recv_initial_metadata
+           .trailing_metadata_available = true;
+    }
     INPROC_LOG(GPR_DEBUG,
                "fail_helper %p scheduling initial-metadata-ready %p %p", s,
                error, err);
@@ -670,6 +678,12 @@ static void op_state_machine(grpc_exec_ctx* exec_ctx, void* arg,
           nullptr);
       s->recv_initial_md_op->payload->recv_initial_metadata
           .recv_initial_metadata->deadline = s->deadline;
+      if (s->recv_initial_md_op->payload->recv_initial_metadata
+              .trailing_metadata_available != nullptr) {
+        *s->recv_initial_md_op->payload->recv_initial_metadata
+             .trailing_metadata_available =
+            (other != nullptr && other->send_trailing_md_op != nullptr);
+      }
       grpc_metadata_batch_clear(exec_ctx, &s->to_read_initial_md);
       s->to_read_initial_md_filled = false;
       INPROC_LOG(GPR_DEBUG,
@@ -995,6 +1009,15 @@ static void perform_stream_op(grpc_exec_ctx* exec_ctx, grpc_transport* gt,
     if (error != GRPC_ERROR_NONE) {
       // Schedule op's closures that we didn't push to op state machine
       if (op->recv_initial_metadata) {
+        if (op->payload->recv_initial_metadata.trailing_metadata_available !=
+            nullptr) {
+          // Set to true unconditionally, because we're failing the call, so
+          // even if we haven't actually seen the send_trailing_metadata op
+          // from the other side, we're going to return trailing metadata
+          // anyway.
+          *op->payload->recv_initial_metadata.trailing_metadata_available =
+              true;
+        }
         INPROC_LOG(
             GPR_DEBUG,
             "perform_stream_op error %p scheduling initial-metadata-ready %p",
diff --git a/src/core/lib/channel/handshaker.cc b/src/core/lib/channel/handshaker.cc
index aae1b35845..58c30b165b 100644
--- a/src/core/lib/channel/handshaker.cc
+++ b/src/core/lib/channel/handshaker.cc
@@ -231,14 +231,16 @@ static void on_timeout(grpc_exec_ctx* exec_ctx, void* arg, grpc_error* error) {
 
 void grpc_handshake_manager_do_handshake(
     grpc_exec_ctx* exec_ctx, grpc_handshake_manager* mgr,
-    grpc_endpoint* endpoint, const grpc_channel_args* channel_args,
-    grpc_millis deadline, grpc_tcp_server_acceptor* acceptor,
-    grpc_iomgr_cb_func on_handshake_done, void* user_data) {
+    grpc_pollset_set* interested_parties, grpc_endpoint* endpoint,
+    const grpc_channel_args* channel_args, grpc_millis deadline,
+    grpc_tcp_server_acceptor* acceptor, grpc_iomgr_cb_func on_handshake_done,
+    void* user_data) {
   gpr_mu_lock(&mgr->mu);
   GPR_ASSERT(mgr->index == 0);
   GPR_ASSERT(!mgr->shutdown);
   // Construct handshaker args.  These will be passed through all
   // handshakers and eventually be freed by the on_handshake_done callback.
+  mgr->args.interested_parties = interested_parties;
   mgr->args.endpoint = endpoint;
   mgr->args.args = grpc_channel_args_copy(channel_args);
   mgr->args.user_data = user_data;
diff --git a/src/core/lib/channel/handshaker.h b/src/core/lib/channel/handshaker.h
index 09b4a27c1c..8e4114dc64 100644
--- a/src/core/lib/channel/handshaker.h
+++ b/src/core/lib/channel/handshaker.h
@@ -54,6 +54,7 @@ typedef struct grpc_handshaker grpc_handshaker;
 /// For the on_handshake_done callback, all members are input arguments,
 /// which the callback takes ownership of.
 typedef struct {
+  grpc_pollset_set* interested_parties;
   grpc_endpoint* endpoint;
   grpc_channel_args* args;
   grpc_slice_buffer* read_buffer;
@@ -131,11 +132,13 @@ void grpc_handshake_manager_shutdown(grpc_exec_ctx* exec_ctx,
                                      grpc_error* why);
 
 /// Invokes handshakers in the order they were added.
+/// \a interested_parties may be non-nullptr to provide a pollset_set that
+/// may be used during handshaking. Ownership is not taken.
 /// Takes ownership of \a endpoint, and then passes that ownership to
 /// the \a on_handshake_done callback.
 /// Does NOT take ownership of \a channel_args.  Instead, makes a copy before
 /// invoking the first handshaker.
-/// \a acceptor will be NULL for client-side handshakers.
+/// \a acceptor will be nullptr for client-side handshakers.
 ///
 /// When done, invokes \a on_handshake_done with a grpc_handshaker_args
 /// object as its argument.  If the callback is invoked with error !=
@@ -144,9 +147,10 @@ void grpc_handshake_manager_shutdown(grpc_exec_ctx* exec_ctx,
 /// the arguments.
 void grpc_handshake_manager_do_handshake(
     grpc_exec_ctx* exec_ctx, grpc_handshake_manager* mgr,
-    grpc_endpoint* endpoint, const grpc_channel_args* channel_args,
-    grpc_millis deadline, grpc_tcp_server_acceptor* acceptor,
-    grpc_iomgr_cb_func on_handshake_done, void* user_data);
+    grpc_pollset_set* interested_parties, grpc_endpoint* endpoint,
+    const grpc_channel_args* channel_args, grpc_millis deadline,
+    grpc_tcp_server_acceptor* acceptor, grpc_iomgr_cb_func on_handshake_done,
+    void* user_data);
 
 /// Add \a mgr to the server side list of all pending handshake managers, the
 /// list starts with \a *head.
diff --git a/src/core/lib/http/httpcli_security_connector.cc b/src/core/lib/http/httpcli_security_connector.cc
index d25fba538f..dfcaee702b 100644
--- a/src/core/lib/http/httpcli_security_connector.cc
+++ b/src/core/lib/http/httpcli_security_connector.cc
@@ -191,8 +191,9 @@ static void ssl_handshake(grpc_exec_ctx* exec_ctx, void* arg,
   c->handshake_mgr = grpc_handshake_manager_create();
   grpc_handshakers_add(exec_ctx, HANDSHAKER_CLIENT, &args, c->handshake_mgr);
   grpc_handshake_manager_do_handshake(
-      exec_ctx, c->handshake_mgr, tcp, nullptr /* channel_args */, deadline,
-      nullptr /* acceptor */, on_handshake_done, c /* user_data */);
+      exec_ctx, c->handshake_mgr, nullptr /* interested_parties */, tcp,
+      nullptr /* channel_args */, deadline, nullptr /* acceptor */,
+      on_handshake_done, c /* user_data */);
   GRPC_SECURITY_CONNECTOR_UNREF(exec_ctx, &sc->base, "httpcli");
 }
 
diff --git a/src/core/lib/iomgr/tcp_server_uv.cc b/src/core/lib/iomgr/tcp_server_uv.cc
index 2c76fae7fd..ffadf0b1ab 100644
--- a/src/core/lib/iomgr/tcp_server_uv.cc
+++ b/src/core/lib/iomgr/tcp_server_uv.cc
@@ -260,15 +260,36 @@ static void on_connect(uv_stream_t* server, int status) {
   grpc_exec_ctx_finish(&exec_ctx);
 }
 
-static grpc_error* add_socket_to_server(grpc_tcp_server* s, uv_tcp_t* handle,
-                                        const grpc_resolved_address* addr,
-                                        unsigned port_index,
-                                        grpc_tcp_listener** listener) {
+static grpc_error* add_addr_to_server(grpc_tcp_server* s,
+                                      const grpc_resolved_address* addr,
+                                      unsigned port_index,
+                                      grpc_tcp_listener** listener) {
   grpc_tcp_listener* sp = NULL;
   int port = -1;
   int status;
   grpc_error* error;
   grpc_resolved_address sockname_temp;
+  uv_tcp_t* handle = (uv_tcp_t*)gpr_malloc(sizeof(uv_tcp_t));
+  int family = grpc_sockaddr_get_family(addr);
+
+  status = uv_tcp_init_ex(uv_default_loop(), handle, (unsigned int)family);
+#if defined(GPR_LINUX) && defined(SO_REUSEPORT)
+  if (family == AF_INET || family == AF_INET6) {
+    int fd;
+    uv_fileno((uv_handle_t*)handle, &fd);
+    int enable = 1;
+    setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, &enable, sizeof(enable));
+  }
+#endif /* GPR_LINUX && SO_REUSEPORT */
+
+  if (status != 0) {
+    error = GRPC_ERROR_CREATE_FROM_STATIC_STRING(
+        "Failed to initialize UV tcp handle");
+    error =
+        grpc_error_set_str(error, GRPC_ERROR_STR_OS_ERROR,
+                           grpc_slice_from_static_string(uv_strerror(status)));
+    return error;
+  }
 
   // The last argument to uv_tcp_bind is flags
   status = uv_tcp_bind(handle, (struct sockaddr*)addr->addr, 0);
@@ -325,20 +346,48 @@ static grpc_error* add_socket_to_server(grpc_tcp_server* s, uv_tcp_t* handle,
   return GRPC_ERROR_NONE;
 }
 
+static grpc_error* add_wildcard_addrs_to_server(grpc_tcp_server* s,
+                                                unsigned port_index,
+                                                int requested_port,
+                                                grpc_tcp_listener** listener) {
+  grpc_resolved_address wild4;
+  grpc_resolved_address wild6;
+  grpc_tcp_listener* sp = nullptr;
+  grpc_tcp_listener* sp2 = nullptr;
+  grpc_error* v6_err = GRPC_ERROR_NONE;
+  grpc_error* v4_err = GRPC_ERROR_NONE;
+
+  grpc_sockaddr_make_wildcards(requested_port, &wild4, &wild6);
+  /* Try listening on IPv6 first. */
+  if ((v6_err = add_addr_to_server(s, &wild6, port_index, &sp)) ==
+      GRPC_ERROR_NONE) {
+    *listener = sp;
+    return GRPC_ERROR_NONE;
+  }
+
+  if ((v4_err = add_addr_to_server(s, &wild4, port_index, &sp2)) ==
+      GRPC_ERROR_NONE) {
+    *listener = sp2;
+    return GRPC_ERROR_NONE;
+  }
+
+  grpc_error* root_err = GRPC_ERROR_CREATE_FROM_STATIC_STRING(
+      "Failed to add any wildcard listeners");
+  root_err = grpc_error_add_child(root_err, v6_err);
+  root_err = grpc_error_add_child(root_err, v4_err);
+  return root_err;
+}
+
 grpc_error* grpc_tcp_server_add_port(grpc_tcp_server* s,
                                      const grpc_resolved_address* addr,
                                      int* port) {
   // This function is mostly copied from tcp_server_windows.c
   grpc_tcp_listener* sp = NULL;
-  uv_tcp_t* handle;
   grpc_resolved_address addr6_v4mapped;
-  grpc_resolved_address wildcard;
   grpc_resolved_address* allocated_addr = NULL;
   grpc_resolved_address sockname_temp;
   unsigned port_index = 0;
-  int status;
   grpc_error* error = GRPC_ERROR_NONE;
-  int family;
 
   GRPC_UV_ASSERT_SAME_THREAD();
 
@@ -367,38 +416,15 @@ grpc_error* grpc_tcp_server_add_port(grpc_tcp_server* s,
     }
   }
 
-  if (grpc_sockaddr_to_v4mapped(addr, &addr6_v4mapped)) {
-    addr = &addr6_v4mapped;
-  }
-
   /* Treat :: or 0.0.0.0 as a family-agnostic wildcard. */
   if (grpc_sockaddr_is_wildcard(addr, port)) {
-    grpc_sockaddr_make_wildcard6(*port, &wildcard);
-
-    addr = &wildcard;
-  }
-
-  handle = (uv_tcp_t*)gpr_malloc(sizeof(uv_tcp_t));
-
-  family = grpc_sockaddr_get_family(addr);
-  status = uv_tcp_init_ex(uv_default_loop(), handle, (unsigned int)family);
-#if defined(GPR_LINUX) && defined(SO_REUSEPORT)
-  if (family == AF_INET || family == AF_INET6) {
-    int fd;
-    uv_fileno((uv_handle_t*)handle, &fd);
-    int enable = 1;
-    setsockopt(fd, SOL_SOCKET, SO_REUSEPORT, &enable, sizeof(enable));
-  }
-#endif /* GPR_LINUX && SO_REUSEPORT */
-
-  if (status == 0) {
-    error = add_socket_to_server(s, handle, addr, port_index, &sp);
+    error = add_wildcard_addrs_to_server(s, port_index, *port, &sp);
   } else {
-    error = GRPC_ERROR_CREATE_FROM_STATIC_STRING(
-        "Failed to initialize UV tcp handle");
-    error =
-        grpc_error_set_str(error, GRPC_ERROR_STR_OS_ERROR,
-                           grpc_slice_from_static_string(uv_strerror(status)));
+    if (grpc_sockaddr_to_v4mapped(addr, &addr6_v4mapped)) {
+      addr = &addr6_v4mapped;
+    }
+
+    error = add_addr_to_server(s, addr, port_index, &sp);
   }
 
   gpr_free(allocated_addr);
diff --git a/src/csharp/generate_proto_csharp.sh b/src/csharp/generate_proto_csharp.sh
index 1a1adbbae5..299dc3f816 100755
--- a/src/csharp/generate_proto_csharp.sh
+++ b/src/csharp/generate_proto_csharp.sh
@@ -33,6 +33,11 @@ $PROTOC --plugin=$PLUGIN --csharp_out=$HEALTHCHECK_DIR --grpc_out=$HEALTHCHECK_D
 $PROTOC --plugin=$PLUGIN --csharp_out=$REFLECTION_DIR --grpc_out=$REFLECTION_DIR \
     -I src/proto src/proto/grpc/reflection/v1alpha/reflection.proto
 
+# Put grp/core/stats.proto in a subdirectory to avoid collision with grpc/testing/stats.proto
+mkdir -p $TESTING_DIR/CoreStats
+$PROTOC --plugin=$PLUGIN --csharp_out=$TESTING_DIR/CoreStats --grpc_out=$TESTING_DIR/CoreStats \
+    -I src/proto src/proto/grpc/core/stats.proto
+
 # TODO(jtattermusch): following .proto files are a bit broken and import paths
 # don't match the package names. Setting -I to the correct value src/proto
 # breaks the code generation.
diff --git a/src/python/grpcio/grpc/__init__.py b/src/python/grpcio/grpc/__init__.py
index 558ce42129..564772527e 100644
--- a/src/python/grpcio/grpc/__init__.py
+++ b/src/python/grpcio/grpc/__init__.py
@@ -348,26 +348,25 @@ class Call(six.with_metaclass(abc.ABCMeta, RpcContext)):
 class ChannelCredentials(object):
     """An encapsulation of the data required to create a secure Channel.
 
-  This class has no supported interface - it exists to define the type of its
-  instances and its instances exist to be passed to other functions. For
-  example, ssl_channel_credentials returns an instance, and secure_channel
-  consumes an instance of this class.
-  """
+    This class has no supported interface - it exists to define the type of its
+    instances and its instances exist to be passed to other functions. For
+    example, ssl_channel_credentials returns an instance of this class and
+    secure_channel requires an instance of this class.
+    """
 
     def __init__(self, credentials):
         self._credentials = credentials
 
 
 class CallCredentials(object):
-    """An encapsulation of the data required to assert an identity over a
-       channel.
+    """An encapsulation of the data required to assert an identity over a call.
 
-  A CallCredentials may be composed with ChannelCredentials to always assert
-  identity for every call over that Channel.
+    A CallCredentials may be composed with ChannelCredentials to always assert
+    identity for every call over that Channel.
 
-  This class has no supported interface - it exists to define the type of its
-  instances and its instances exist to be passed to other functions.
-  """
+    This class has no supported interface - it exists to define the type of its
+    instances and its instances exist to be passed to other functions.
+    """
 
     def __init__(self, credentials):
         self._credentials = credentials
@@ -376,23 +375,22 @@ class CallCredentials(object):
 class AuthMetadataContext(six.with_metaclass(abc.ABCMeta)):
     """Provides information to call credentials metadata plugins.
 
-  Attributes:
-    service_url: A string URL of the service being called into.
-    method_name: A string of the fully qualified method name being called.
-  """
+    Attributes:
+      service_url: A string URL of the service being called into.
+      method_name: A string of the fully qualified method name being called.
+    """
 
 
 class AuthMetadataPluginCallback(six.with_metaclass(abc.ABCMeta)):
     """Callback object received by a metadata plugin."""
 
     def __call__(self, metadata, error):
-        """Inform the gRPC runtime of the metadata to construct a
-           CallCredentials.
+        """Passes to the gRPC runtime authentication metadata for an RPC.
 
-    Args:
-      metadata: The :term:`metadata` used to construct the CallCredentials.
-      error: An Exception to indicate error or None to indicate success.
-    """
+        Args:
+          metadata: The :term:`metadata` used to construct the CallCredentials.
+          error: An Exception to indicate error or None to indicate success.
+        """
         raise NotImplementedError()
 
 
@@ -402,14 +400,14 @@ class AuthMetadataPlugin(six.with_metaclass(abc.ABCMeta)):
     def __call__(self, context, callback):
         """Implements authentication by passing metadata to a callback.
 
-    Implementations of this method must not block.
+        Implementations of this method must not block.
 
-    Args:
-      context: An AuthMetadataContext providing information on the RPC that the
-        plugin is being called to authenticate.
-      callback: An AuthMetadataPluginCallback to be invoked either synchronously
-        or asynchronously.
-    """
+        Args:
+          context: An AuthMetadataContext providing information on the RPC that
+            the plugin is being called to authenticate.
+          callback: An AuthMetadataPluginCallback to be invoked either
+            synchronously or asynchronously.
+        """
         raise NotImplementedError()
 
 
@@ -1138,99 +1136,86 @@ def ssl_channel_credentials(root_certificates=None,
                             certificate_chain=None):
     """Creates a ChannelCredentials for use with an SSL-enabled Channel.
 
-  Args:
-    root_certificates: The PEM-encoded root certificates as a byte string,
-    or None to retrieve them from a default location chosen by gRPC runtime.
-    private_key: The PEM-encoded private key as a byte string, or None if no
-    private key should be used.
-    certificate_chain: The PEM-encoded certificate chain as a byte string
-    to use or or None if no certificate chain should be used.
+    Args:
+      root_certificates: The PEM-encoded root certificates as a byte string,
+        or None to retrieve them from a default location chosen by gRPC
+        runtime.
+      private_key: The PEM-encoded private key as a byte string, or None if no
+        private key should be used.
+      certificate_chain: The PEM-encoded certificate chain as a byte string
+        to use or or None if no certificate chain should be used.
 
-  Returns:
-    A ChannelCredentials for use with an SSL-enabled Channel.
-  """
-    if private_key is not None or certificate_chain is not None:
-        pair = _cygrpc.SslPemKeyCertPair(private_key, certificate_chain)
-    else:
-        pair = None
+    Returns:
+      A ChannelCredentials for use with an SSL-enabled Channel.
+    """
     return ChannelCredentials(
-        _cygrpc.channel_credentials_ssl(root_certificates, pair))
+        _cygrpc.SSLChannelCredentials(root_certificates, private_key,
+                                      certificate_chain))
 
 
 def metadata_call_credentials(metadata_plugin, name=None):
     """Construct CallCredentials from an AuthMetadataPlugin.
 
-  Args:
-    metadata_plugin: An AuthMetadataPlugin to use for authentication.
-    name: An optional name for the plugin.
+    Args:
+      metadata_plugin: An AuthMetadataPlugin to use for authentication.
+      name: An optional name for the plugin.
 
-  Returns:
-    A CallCredentials.
-  """
+    Returns:
+      A CallCredentials.
+    """
     from grpc import _plugin_wrapping  # pylint: disable=cyclic-import
-    if name is None:
-        try:
-            effective_name = metadata_plugin.__name__
-        except AttributeError:
-            effective_name = metadata_plugin.__class__.__name__
-    else:
-        effective_name = name
-    return CallCredentials(
-        _plugin_wrapping.call_credentials_metadata_plugin(metadata_plugin,
-                                                          effective_name))
+    return _plugin_wrapping.metadata_plugin_call_credentials(metadata_plugin,
+                                                             name)
 
 
 def access_token_call_credentials(access_token):
     """Construct CallCredentials from an access token.
 
-  Args:
-    access_token: A string to place directly in the http request
-      authorization header, for example
-      "authorization: Bearer <access_token>".
+    Args:
+      access_token: A string to place directly in the http request
+        authorization header, for example
+        "authorization: Bearer <access_token>".
 
-  Returns:
-    A CallCredentials.
-  """
+    Returns:
+      A CallCredentials.
+    """
     from grpc import _auth  # pylint: disable=cyclic-import
-    return metadata_call_credentials(
-        _auth.AccessTokenCallCredentials(access_token))
+    from grpc import _plugin_wrapping  # pylint: disable=cyclic-import
+    return _plugin_wrapping.metadata_plugin_call_credentials(
+        _auth.AccessTokenAuthMetadataPlugin(access_token), None)
 
 
 def composite_call_credentials(*call_credentials):
     """Compose multiple CallCredentials to make a new CallCredentials.
 
-  Args:
-    *call_credentials: At least two CallCredentials objects.
+    Args:
+      *call_credentials: At least two CallCredentials objects.
 
-  Returns:
-    A CallCredentials object composed of the given CallCredentials objects.
-  """
-    from grpc import _credential_composition  # pylint: disable=cyclic-import
-    cygrpc_call_credentials = tuple(
-        single_call_credentials._credentials
-        for single_call_credentials in call_credentials)
+    Returns:
+      A CallCredentials object composed of the given CallCredentials objects.
+    """
     return CallCredentials(
-        _credential_composition.call(cygrpc_call_credentials))
+        _cygrpc.CompositeCallCredentials(
+            tuple(single_call_credentials._credentials
+                  for single_call_credentials in call_credentials)))
 
 
 def composite_channel_credentials(channel_credentials, *call_credentials):
     """Compose a ChannelCredentials and one or more CallCredentials objects.
 
-  Args:
-    channel_credentials: A ChannelCredentials object.
-    *call_credentials: One or more CallCredentials objects.
+    Args:
+      channel_credentials: A ChannelCredentials object.
+      *call_credentials: One or more CallCredentials objects.
 
-  Returns:
-    A ChannelCredentials composed of the given ChannelCredentials and
-    CallCredentials objects.
-  """
-    from grpc import _credential_composition  # pylint: disable=cyclic-import
-    cygrpc_call_credentials = tuple(
-        single_call_credentials._credentials
-        for single_call_credentials in call_credentials)
+    Returns:
+      A ChannelCredentials composed of the given ChannelCredentials and
+        CallCredentials objects.
+    """
     return ChannelCredentials(
-        _credential_composition.channel(channel_credentials._credentials,
-                                        cygrpc_call_credentials))
+        _cygrpc.CompositeChannelCredentials(
+            tuple(single_call_credentials._credentials
+                  for single_call_credentials in call_credentials),
+            channel_credentials._credentials))
 
 
 def ssl_server_credentials(private_key_certificate_chain_pairs,
diff --git a/src/python/grpcio/grpc/_auth.py b/src/python/grpcio/grpc/_auth.py
index c6542d0135..9a339b5900 100644
--- a/src/python/grpcio/grpc/_auth.py
+++ b/src/python/grpcio/grpc/_auth.py
@@ -63,7 +63,7 @@ class GoogleCallCredentials(grpc.AuthMetadataPlugin):
         self._pool.shutdown(wait=False)
 
 
-class AccessTokenCallCredentials(grpc.AuthMetadataPlugin):
+class AccessTokenAuthMetadataPlugin(grpc.AuthMetadataPlugin):
     """Metadata wrapper for raw access token credentials."""
 
     def __init__(self, access_token):
diff --git a/src/python/grpcio/grpc/_credential_composition.py b/src/python/grpcio/grpc/_credential_composition.py
deleted file mode 100644
index f652cc3ae7..0000000000
--- a/src/python/grpcio/grpc/_credential_composition.py
+++ /dev/null
@@ -1,33 +0,0 @@
-# Copyright 2016 gRPC authors.
-#
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     http://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
-
-from grpc._cython import cygrpc
-
-
-def _call(call_credentialses):
-    call_credentials_iterator = iter(call_credentialses)
-    composition = next(call_credentials_iterator)
-    for additional_call_credentials in call_credentials_iterator:
-        composition = cygrpc.call_credentials_composite(
-            composition, additional_call_credentials)
-    return composition
-
-
-def call(call_credentialses):
-    return _call(call_credentialses)
-
-
-def channel(channel_credentials, call_credentialses):
-    return cygrpc.channel_credentials_composite(channel_credentials,
-                                                _call(call_credentialses))
diff --git a/src/python/grpcio/grpc/_cython/_cygrpc/call.pyx.pxi b/src/python/grpcio/grpc/_cython/_cygrpc/call.pyx.pxi
index 752fb330d0..6b3a276097 100644
--- a/src/python/grpcio/grpc/_cython/_cygrpc/call.pyx.pxi
+++ b/src/python/grpcio/grpc/_cython/_cygrpc/call.pyx.pxi
@@ -72,13 +72,12 @@ cdef class Call:
         result = grpc_call_cancel(self.c_call, NULL)
       return result
 
-  def set_credentials(
-      self, CallCredentials call_credentials not None):
-    cdef grpc_call_error result
-    with nogil:
-      result = grpc_call_set_credentials(
-          self.c_call, call_credentials.c_credentials)
-    return result
+  def set_credentials(self, CallCredentials call_credentials not None):
+    cdef grpc_call_credentials *c_call_credentials = call_credentials.c()
+    cdef grpc_call_error call_error = grpc_call_set_credentials(
+        self.c_call, c_call_credentials)
+    grpc_call_credentials_release(c_call_credentials)
+    return call_error
 
   def peer(self):
     cdef char *peer = NULL
diff --git a/src/python/grpcio/grpc/_cython/_cygrpc/channel.pyx.pxi b/src/python/grpcio/grpc/_cython/_cygrpc/channel.pyx.pxi
index aeabdba021..4c397f8f64 100644
--- a/src/python/grpcio/grpc/_cython/_cygrpc/channel.pyx.pxi
+++ b/src/python/grpcio/grpc/_cython/_cygrpc/channel.pyx.pxi
@@ -33,10 +33,10 @@ cdef class Channel:
         self.c_channel = grpc_insecure_channel_create(c_target, c_arguments,
                                                       NULL)
     else:
-      with nogil:
-        self.c_channel = grpc_secure_channel_create(
-            channel_credentials.c_credentials, c_target, c_arguments, NULL)
-      self.references.append(channel_credentials)
+      c_channel_credentials = channel_credentials.c()
+      self.c_channel = grpc_secure_channel_create(
+          c_channel_credentials, c_target, c_arguments, NULL)
+      grpc_channel_credentials_release(c_channel_credentials)
     self.references.append(target)
     self.references.append(arguments)
 
diff --git a/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pxd.pxi b/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pxd.pxi
index bc0f185c77..7e9ea33ca0 100644
--- a/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pxd.pxi
+++ b/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pxd.pxi
@@ -12,20 +12,66 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-cimport cpython
+
+cdef class CallCredentials:
+
+  cdef grpc_call_credentials *c(self)
+
+  # TODO(https://github.com/grpc/grpc/issues/12531): remove.
+  cdef grpc_call_credentials *c_credentials
+
+
+cdef int _get_metadata(
+    void *state, grpc_auth_metadata_context context,
+    grpc_credentials_plugin_metadata_cb cb, void *user_data,
+    grpc_metadata creds_md[GRPC_METADATA_CREDENTIALS_PLUGIN_SYNC_MAX],
+    size_t *num_creds_md, grpc_status_code *status,
+    const char **error_details) with gil
+
+cdef void _destroy(void *state) with gil
+
+
+cdef class MetadataPluginCallCredentials(CallCredentials):
+
+  cdef readonly object _metadata_plugin
+  cdef readonly bytes _name
+
+  cdef grpc_call_credentials *c(self)
+
+
+cdef grpc_call_credentials *_composition(call_credentialses)
+
+
+cdef class CompositeCallCredentials(CallCredentials):
+
+  cdef readonly tuple _call_credentialses
+
+  cdef grpc_call_credentials *c(self)
 
 
 cdef class ChannelCredentials:
 
+  cdef grpc_channel_credentials *c(self)
+
+  # TODO(https://github.com/grpc/grpc/issues/12531): remove.
   cdef grpc_channel_credentials *c_credentials
-  cdef grpc_ssl_pem_key_cert_pair c_ssl_pem_key_cert_pair
-  cdef list references
 
 
-cdef class CallCredentials:
+cdef class SSLChannelCredentials(ChannelCredentials):
 
-  cdef grpc_call_credentials *c_credentials
-  cdef list references
+  cdef readonly object _pem_root_certificates
+  cdef readonly object _private_key
+  cdef readonly object _certificate_chain
+
+  cdef grpc_channel_credentials *c(self)
+
+
+cdef class CompositeChannelCredentials(ChannelCredentials):
+
+  cdef readonly tuple _call_credentialses
+  cdef readonly ChannelCredentials _channel_credentials
+
+  cdef grpc_channel_credentials *c(self)
 
 
 cdef class ServerCertificateConfig:
@@ -49,27 +95,3 @@ cdef class ServerCredentials:
   cdef object cert_config_fetcher
   # whether C-core has asked for the initial_cert_config
   cdef bint initial_cert_config_fetched
-
-
-cdef class CredentialsMetadataPlugin:
-
-  cdef object plugin_callback
-  cdef bytes plugin_name
-
-
-cdef grpc_metadata_credentials_plugin _c_plugin(CredentialsMetadataPlugin plugin)
-
-
-cdef class AuthMetadataContext:
-
-  cdef grpc_auth_metadata_context context
-
-
-cdef int plugin_get_metadata(
-    void *state, grpc_auth_metadata_context context,
-    grpc_credentials_plugin_metadata_cb cb, void *user_data,
-    grpc_metadata creds_md[GRPC_METADATA_CREDENTIALS_PLUGIN_SYNC_MAX],
-    size_t *num_creds_md, grpc_status_code *status,
-    const char **error_details) with gil
-
-cdef void plugin_destroy_c_plugin_state(void *state) with gil
diff --git a/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pyx.pxi b/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pyx.pxi
index ee1328d2e9..246a271893 100644
--- a/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pyx.pxi
+++ b/src/python/grpcio/grpc/_cython/_cygrpc/credentials.pyx.pxi
@@ -16,47 +16,123 @@ cimport cpython
 
 import grpc
 import threading
-import traceback
 
 
-cdef class ChannelCredentials:
+cdef class CallCredentials:
 
-  def __cinit__(self):
-    grpc_init()
-    self.c_credentials = NULL
-    self.c_ssl_pem_key_cert_pair.private_key = NULL
-    self.c_ssl_pem_key_cert_pair.certificate_chain = NULL
-    self.references = []
+  cdef grpc_call_credentials *c(self):
+    raise NotImplementedError()
 
-  # The object *can* be invalid in Python if we fail to make the credentials
-  # (and the core thus returns NULL credentials). Used primarily for debugging.
-  @property
-  def is_valid(self):
-    return self.c_credentials != NULL
 
-  def __dealloc__(self):
-    if self.c_credentials != NULL:
-      grpc_channel_credentials_release(self.c_credentials)
-    grpc_shutdown()
+cdef int _get_metadata(
+    void *state, grpc_auth_metadata_context context,
+    grpc_credentials_plugin_metadata_cb cb, void *user_data,
+    grpc_metadata creds_md[GRPC_METADATA_CREDENTIALS_PLUGIN_SYNC_MAX],
+    size_t *num_creds_md, grpc_status_code *status,
+    const char **error_details) with gil:
+  def callback(Metadata metadata, grpc_status_code status, bytes error_details):
+    if status is StatusCode.ok:
+      cb(user_data, metadata.c_metadata, metadata.c_count, status, NULL)
+    else:
+      cb(user_data, NULL, 0, status, error_details)
+  args = context.service_url, context.method_name, callback,
+  threading.Thread(target=<object>state, args=args).start()
+  return 0  # Asynchronous return
 
 
-cdef class CallCredentials:
+cdef void _destroy(void *state) with gil:
+  cpython.Py_DECREF(<object>state)
 
-  def __cinit__(self):
-    grpc_init()
-    self.c_credentials = NULL
-    self.references = []
 
-  # The object *can* be invalid in Python if we fail to make the credentials
-  # (and the core thus returns NULL credentials). Used primarily for debugging.
-  @property
-  def is_valid(self):
-    return self.c_credentials != NULL
+cdef class MetadataPluginCallCredentials(CallCredentials):
 
-  def __dealloc__(self):
-    if self.c_credentials != NULL:
-      grpc_call_credentials_release(self.c_credentials)
-    grpc_shutdown()
+  def __cinit__(self, metadata_plugin, name):
+    self._metadata_plugin = metadata_plugin
+    self._name = name
+
+  cdef grpc_call_credentials *c(self):
+    cdef grpc_metadata_credentials_plugin c_metadata_plugin
+    c_metadata_plugin.get_metadata = _get_metadata
+    c_metadata_plugin.destroy = _destroy
+    c_metadata_plugin.state = <void *>self._metadata_plugin
+    c_metadata_plugin.type = self._name
+    cpython.Py_INCREF(self._metadata_plugin)
+    return grpc_metadata_credentials_create_from_plugin(c_metadata_plugin, NULL)
+
+
+cdef grpc_call_credentials *_composition(call_credentialses):
+  call_credentials_iterator = iter(call_credentialses)
+  cdef CallCredentials composition = next(call_credentials_iterator)
+  cdef grpc_call_credentials *c_composition = composition.c()
+  cdef CallCredentials additional_call_credentials
+  cdef grpc_call_credentials *c_additional_call_credentials
+  cdef grpc_call_credentials *c_next_composition
+  for additional_call_credentials in call_credentials_iterator:
+    c_additional_call_credentials = additional_call_credentials.c()
+    c_next_composition = grpc_composite_call_credentials_create(
+        c_composition, c_additional_call_credentials, NULL)
+    grpc_call_credentials_release(c_composition)
+    grpc_call_credentials_release(c_additional_call_credentials)
+    c_composition = c_next_composition
+  return c_composition
+
+
+cdef class CompositeCallCredentials(CallCredentials):
+
+  def __cinit__(self, call_credentialses):
+    self._call_credentialses = call_credentialses
+
+  cdef grpc_call_credentials *c(self):
+    return _composition(self._call_credentialses)
+
+
+cdef class ChannelCredentials:
+
+  cdef grpc_channel_credentials *c(self):
+    raise NotImplementedError()
+
+
+cdef class SSLChannelCredentials(ChannelCredentials):
+
+  def __cinit__(self, pem_root_certificates, private_key, certificate_chain):
+    self._pem_root_certificates = pem_root_certificates
+    self._private_key = private_key
+    self._certificate_chain = certificate_chain
+
+  cdef grpc_channel_credentials *c(self):
+    cdef const char *c_pem_root_certificates
+    cdef grpc_ssl_pem_key_cert_pair c_pem_key_certificate_pair
+    if self._pem_root_certificates is None:
+      c_pem_root_certificates = NULL
+    else:
+      c_pem_root_certificates = self._pem_root_certificates
+    if self._private_key is None and self._certificate_chain is None:
+      return grpc_ssl_credentials_create(
+          c_pem_root_certificates, NULL, NULL)
+    else:
+      c_pem_key_certificate_pair.private_key = self._private_key
+      c_pem_key_certificate_pair.certificate_chain = self._certificate_chain
+      return grpc_ssl_credentials_create(
+          c_pem_root_certificates, &c_pem_key_certificate_pair, NULL)
+
+
+cdef class CompositeChannelCredentials(ChannelCredentials):
+
+  def __cinit__(self, call_credentialses, channel_credentials):
+    self._call_credentialses = call_credentialses
+    self._channel_credentials = channel_credentials
+
+  cdef grpc_channel_credentials *c(self):
+    cdef grpc_channel_credentials *c_channel_credentials
+    c_channel_credentials = self._channel_credentials.c()
+    cdef grpc_call_credentials *c_call_credentials_composition = _composition(
+        self._call_credentialses)
+    cdef grpc_channel_credentials *composition
+    c_composition = grpc_composite_channel_credentials_create(
+        c_channel_credentials, c_call_credentials_composition, NULL)
+    grpc_channel_credentials_release(c_channel_credentials)
+    grpc_call_credentials_release(c_call_credentials_composition)
+    return c_composition
 
 
 cdef class ServerCertificateConfig:
@@ -89,190 +165,6 @@ cdef class ServerCredentials:
       grpc_server_credentials_release(self.c_credentials)
     grpc_shutdown()
 
-
-cdef class CredentialsMetadataPlugin:
-
-  def __cinit__(self, object plugin_callback, bytes name):
-    """
-    Args:
-      plugin_callback (callable): Callback accepting a service URL (str/bytes)
-        and callback object (accepting a MetadataArray,
-        grpc_status_code, and a str/bytes error message). This argument
-        when called should be non-blocking and eventually call the callback
-        object with the appropriate status code/details and metadata (if
-        successful).
-      name (bytes): Plugin name.
-    """
-    grpc_init()
-    if not callable(plugin_callback):
-      raise ValueError('expected callable plugin_callback')
-    self.plugin_callback = plugin_callback
-    self.plugin_name = name
-
-  def __dealloc__(self):
-    grpc_shutdown()
-
-
-cdef grpc_metadata_credentials_plugin _c_plugin(CredentialsMetadataPlugin plugin):
-  cdef grpc_metadata_credentials_plugin c_plugin
-  c_plugin.get_metadata = plugin_get_metadata
-  c_plugin.destroy = plugin_destroy_c_plugin_state
-  c_plugin.state = <void *>plugin
-  c_plugin.type = plugin.plugin_name
-  cpython.Py_INCREF(plugin)
-  return c_plugin
-
-
-cdef class AuthMetadataContext:
-
-  def __cinit__(self):
-    grpc_init()
-    self.context.service_url = NULL
-    self.context.method_name = NULL
-
-  @property
-  def service_url(self):
-    return self.context.service_url
-
-  @property
-  def method_name(self):
-    return self.context.method_name
-
-  def __dealloc__(self):
-    grpc_shutdown()
-
-
-cdef int plugin_get_metadata(
-    void *state, grpc_auth_metadata_context context,
-    grpc_credentials_plugin_metadata_cb cb, void *user_data,
-    grpc_metadata creds_md[GRPC_METADATA_CREDENTIALS_PLUGIN_SYNC_MAX],
-    size_t *num_creds_md, grpc_status_code *status,
-    const char **error_details) with gil:
-  called_flag = [False]
-  def python_callback(
-      Metadata metadata, grpc_status_code status,
-      bytes error_details):
-    cb(user_data, metadata.c_metadata, metadata.c_count, status, error_details)
-    called_flag[0] = True
-  cdef CredentialsMetadataPlugin self = <CredentialsMetadataPlugin>state
-  cdef AuthMetadataContext cy_context = AuthMetadataContext()
-  cy_context.context = context
-  def async_callback():
-    try:
-      self.plugin_callback(cy_context, python_callback)
-    except Exception as error:
-      if not called_flag[0]:
-        cb(user_data, NULL, 0, StatusCode.unknown,
-           traceback.format_exc().encode())
-  threading.Thread(group=None, target=async_callback).start()
-  return 0  # Asynchronous return
-
-cdef void plugin_destroy_c_plugin_state(void *state) with gil:
-  cpython.Py_DECREF(<CredentialsMetadataPlugin>state)
-
-def channel_credentials_google_default():
-  cdef ChannelCredentials credentials = ChannelCredentials();
-  with nogil:
-    credentials.c_credentials = grpc_google_default_credentials_create()
-  return credentials
-
-def channel_credentials_ssl(pem_root_certificates,
-                            SslPemKeyCertPair ssl_pem_key_cert_pair):
-  pem_root_certificates = str_to_bytes(pem_root_certificates)
-  cdef ChannelCredentials credentials = ChannelCredentials()
-  cdef const char *c_pem_root_certificates = NULL
-  if pem_root_certificates is not None:
-    c_pem_root_certificates = pem_root_certificates
-    credentials.references.append(pem_root_certificates)
-  if ssl_pem_key_cert_pair is not None:
-    with nogil:
-      credentials.c_credentials = grpc_ssl_credentials_create(
-          c_pem_root_certificates, &ssl_pem_key_cert_pair.c_pair, NULL)
-    credentials.references.append(ssl_pem_key_cert_pair)
-  else:
-    with nogil:
-      credentials.c_credentials = grpc_ssl_credentials_create(
-        c_pem_root_certificates, NULL, NULL)
-  return credentials
-
-def channel_credentials_composite(
-    ChannelCredentials credentials_1 not None,
-    CallCredentials credentials_2 not None):
-  if not credentials_1.is_valid or not credentials_2.is_valid:
-    raise ValueError("passed credentials must both be valid")
-  cdef ChannelCredentials credentials = ChannelCredentials()
-  with nogil:
-    credentials.c_credentials = grpc_composite_channel_credentials_create(
-        credentials_1.c_credentials, credentials_2.c_credentials, NULL)
-  credentials.references.append(credentials_1)
-  credentials.references.append(credentials_2)
-  return credentials
-
-def call_credentials_composite(
-    CallCredentials credentials_1 not None,
-    CallCredentials credentials_2 not None):
-  if not credentials_1.is_valid or not credentials_2.is_valid:
-    raise ValueError("passed credentials must both be valid")
-  cdef CallCredentials credentials = CallCredentials()
-  with nogil:
-    credentials.c_credentials = grpc_composite_call_credentials_create(
-        credentials_1.c_credentials, credentials_2.c_credentials, NULL)
-  credentials.references.append(credentials_1)
-  credentials.references.append(credentials_2)
-  return credentials
-
-def call_credentials_google_compute_engine():
-  cdef CallCredentials credentials = CallCredentials()
-  with nogil:
-    credentials.c_credentials = (
-        grpc_google_compute_engine_credentials_create(NULL))
-  return credentials
-
-def call_credentials_service_account_jwt_access(
-    json_key, Timespec token_lifetime not None):
-  json_key = str_to_bytes(json_key)
-  cdef CallCredentials credentials = CallCredentials()
-  cdef char *json_key_c_string = json_key
-  with nogil:
-    credentials.c_credentials = (
-        grpc_service_account_jwt_access_credentials_create(
-            json_key_c_string, token_lifetime.c_time, NULL))
-  credentials.references.append(json_key)
-  return credentials
-
-def call_credentials_google_refresh_token(json_refresh_token):
-  json_refresh_token = str_to_bytes(json_refresh_token)
-  cdef CallCredentials credentials = CallCredentials()
-  cdef char *json_refresh_token_c_string = json_refresh_token
-  with nogil:
-    credentials.c_credentials = grpc_google_refresh_token_credentials_create(
-        json_refresh_token_c_string, NULL)
-  credentials.references.append(json_refresh_token)
-  return credentials
-
-def call_credentials_google_iam(authorization_token, authority_selector):
-  authorization_token = str_to_bytes(authorization_token)
-  authority_selector = str_to_bytes(authority_selector)
-  cdef CallCredentials credentials = CallCredentials()
-  cdef char *authorization_token_c_string = authorization_token
-  cdef char *authority_selector_c_string = authority_selector
-  with nogil:
-    credentials.c_credentials = grpc_google_iam_credentials_create(
-        authorization_token_c_string, authority_selector_c_string, NULL)
-  credentials.references.append(authorization_token)
-  credentials.references.append(authority_selector)
-  return credentials
-
-def call_credentials_metadata_plugin(CredentialsMetadataPlugin plugin):
-  cdef CallCredentials credentials = CallCredentials()
-  cdef grpc_metadata_credentials_plugin c_plugin = _c_plugin(plugin)
-  with nogil:
-    credentials.c_credentials = (
-        grpc_metadata_credentials_create_from_plugin(c_plugin, NULL))
-  # TODO(atash): the following held reference is *probably* never necessary
-  credentials.references.append(plugin)
-  return credentials
-
 cdef const char* _get_c_pem_root_certs(pem_root_certs):
   if pem_root_certs is None:
     return NULL
diff --git a/src/python/grpcio/grpc/_plugin_wrapping.py b/src/python/grpcio/grpc/_plugin_wrapping.py
index bea2c0f139..cd17f4a049 100644
--- a/src/python/grpcio/grpc/_plugin_wrapping.py
+++ b/src/python/grpcio/grpc/_plugin_wrapping.py
@@ -13,6 +13,7 @@
 # limitations under the License.
 
 import collections
+import logging
 import threading
 
 import grpc
@@ -20,89 +21,79 @@ from grpc import _common
 from grpc._cython import cygrpc
 
 
-class AuthMetadataContext(
+class _AuthMetadataContext(
         collections.namedtuple('AuthMetadataContext', (
             'service_url', 'method_name',)), grpc.AuthMetadataContext):
     pass
 
 
-class AuthMetadataPluginCallback(grpc.AuthMetadataContext):
+class _CallbackState(object):
 
-    def __init__(self, callback):
-        self._callback = callback
-
-    def __call__(self, metadata, error):
-        self._callback(metadata, error)
+    def __init__(self):
+        self.lock = threading.Lock()
+        self.called = False
+        self.exception = None
 
 
-class _WrappedCygrpcCallback(object):
+class _AuthMetadataPluginCallback(grpc.AuthMetadataPluginCallback):
 
-    def __init__(self, cygrpc_callback):
-        self.is_called = False
-        self.error = None
-        self.is_called_lock = threading.Lock()
-        self.cygrpc_callback = cygrpc_callback
-
-    def _invoke_failure(self, error):
-        # TODO(atash) translate different Exception superclasses into different
-        # status codes.
-        self.cygrpc_callback(_common.EMPTY_METADATA, cygrpc.StatusCode.internal,
-                             _common.encode(str(error)))
-
-    def _invoke_success(self, metadata):
-        try:
-            cygrpc_metadata = _common.to_cygrpc_metadata(metadata)
-        except Exception as exception:  # pylint: disable=broad-except
-            self._invoke_failure(exception)
-            return
-        self.cygrpc_callback(cygrpc_metadata, cygrpc.StatusCode.ok, b'')
+    def __init__(self, state, callback):
+        self._state = state
+        self._callback = callback
 
     def __call__(self, metadata, error):
-        with self.is_called_lock:
-            if self.is_called:
-                raise RuntimeError('callback should only ever be invoked once')
-            if self.error:
-                self._invoke_failure(self.error)
-                return
-            self.is_called = True
+        with self._state.lock:
+            if self._state.exception is None:
+                if self._state.called:
+                    raise RuntimeError(
+                        'AuthMetadataPluginCallback invoked more than once!')
+                else:
+                    self._state.called = True
+            else:
+                raise RuntimeError(
+                    'AuthMetadataPluginCallback raised exception "{}"!'.format(
+                        self._state.exception))
         if error is None:
-            self._invoke_success(metadata)
+            self._callback(
+                _common.to_cygrpc_metadata(metadata), cygrpc.StatusCode.ok,
+                None)
         else:
-            self._invoke_failure(error)
-
-    def notify_failure(self, error):
-        with self.is_called_lock:
-            if not self.is_called:
-                self.error = error
+            self._callback(None, cygrpc.StatusCode.internal,
+                           _common.encode(str(error)))
 
 
-class _WrappedPlugin(object):
+class _Plugin(object):
 
-    def __init__(self, plugin):
-        self.plugin = plugin
+    def __init__(self, metadata_plugin):
+        self._metadata_plugin = metadata_plugin
 
-    def __call__(self, context, cygrpc_callback):
-        wrapped_cygrpc_callback = _WrappedCygrpcCallback(cygrpc_callback)
-        wrapped_context = AuthMetadataContext(
-            _common.decode(context.service_url),
-            _common.decode(context.method_name))
+    def __call__(self, service_url, method_name, callback):
+        context = _AuthMetadataContext(
+            _common.decode(service_url), _common.decode(method_name))
+        callback_state = _CallbackState()
+        try:
+            self._metadata_plugin(
+                context, _AuthMetadataPluginCallback(callback_state, callback))
+        except Exception as exception:  # pylint: disable=broad-except
+            logging.exception(
+                'AuthMetadataPluginCallback "%s" raised exception!',
+                self._metadata_plugin)
+            with callback_state.lock:
+                callback_state.exception = exception
+                if callback_state.called:
+                    return
+            callback(None, cygrpc.StatusCode.internal,
+                     _common.encode(str(exception)))
+
+
+def metadata_plugin_call_credentials(metadata_plugin, name):
+    if name is None:
         try:
-            self.plugin(wrapped_context,
-                        AuthMetadataPluginCallback(wrapped_cygrpc_callback))
-        except Exception as error:
-            wrapped_cygrpc_callback.notify_failure(error)
-            raise
-
-
-def call_credentials_metadata_plugin(plugin, name):
-    """
-  Args:
-    plugin: A callable accepting a grpc.AuthMetadataContext
-      object and a callback (itself accepting a list of metadata key/value
-      2-tuples and a None-able exception value). The callback must be eventually
-      called, but need not be called in plugin's invocation.
-      plugin's invocation must be non-blocking.
-  """
-    return cygrpc.call_credentials_metadata_plugin(
-        cygrpc.CredentialsMetadataPlugin(
-            _WrappedPlugin(plugin), _common.encode(name)))
+            effective_name = metadata_plugin.__name__
+        except AttributeError:
+            effective_name = metadata_plugin.__class__.__name__
+    else:
+        effective_name = name
+    return grpc.CallCredentials(
+        cygrpc.MetadataPluginCallCredentials(
+            _Plugin(metadata_plugin), _common.encode(effective_name)))
diff --git a/src/python/grpcio/grpc/_server.py b/src/python/grpcio/grpc/_server.py
index cd59b07c04..5b4812bffe 100644
--- a/src/python/grpcio/grpc/_server.py
+++ b/src/python/grpcio/grpc/_server.py
@@ -374,10 +374,10 @@ def _call_behavior(rpc_event, state, behavior, argument, request_deserializer):
     context = _Context(rpc_event, state, request_deserializer)
     try:
         return behavior(argument, context), True
-    except Exception as e:  # pylint: disable=broad-except
+    except Exception as exception:  # pylint: disable=broad-except
         with state.condition:
-            if e not in state.rpc_errors:
-                details = 'Exception calling application: {}'.format(e)
+            if exception not in state.rpc_errors:
+                details = 'Exception calling application: {}'.format(exception)
                 logging.exception(details)
                 _abort(state, rpc_event.operation_call,
                        cygrpc.StatusCode.unknown, _common.encode(details))
@@ -389,10 +389,10 @@ def _take_response_from_response_iterator(rpc_event, state, response_iterator):
         return next(response_iterator), True
     except StopIteration:
         return None, True
-    except Exception as e:  # pylint: disable=broad-except
+    except Exception as exception:  # pylint: disable=broad-except
         with state.condition:
-            if e not in state.rpc_errors:
-                details = 'Exception iterating responses: {}'.format(e)
+            if exception not in state.rpc_errors:
+                details = 'Exception iterating responses: {}'.format(exception)
                 logging.exception(details)
                 _abort(state, rpc_event.operation_call,
                        cygrpc.StatusCode.unknown, _common.encode(details))
@@ -591,7 +591,13 @@ def _handle_call(rpc_event, generic_handlers, thread_pool,
     if not rpc_event.success:
         return None, None
     if rpc_event.request_call_details.method is not None:
-        method_handler = _find_method_handler(rpc_event, generic_handlers)
+        try:
+            method_handler = _find_method_handler(rpc_event, generic_handlers)
+        except Exception as exception:  # pylint: disable=broad-except
+            details = 'Exception servicing handler: {}'.format(exception)
+            logging.exception(details)
+            return _reject_rpc(rpc_event, cygrpc.StatusCode.unknown,
+                               b'Error in service handler!'), None
         if method_handler is None:
             return _reject_rpc(rpc_event, cygrpc.StatusCode.unimplemented,
                                b'Method not found!'), None
diff --git a/src/python/grpcio_tests/tests/tests.json b/src/python/grpcio_tests/tests/tests.json
index e277a3ea1d..34cbade92c 100644
--- a/src/python/grpcio_tests/tests/tests.json
+++ b/src/python/grpcio_tests/tests/tests.json
@@ -22,7 +22,7 @@
   "unit._api_test.ChannelConnectivityTest",
   "unit._api_test.ChannelTest",
   "unit._auth_context_test.AuthContextTest",
-  "unit._auth_test.AccessTokenCallCredentialsTest",
+  "unit._auth_test.AccessTokenAuthMetadataPluginTest",
   "unit._auth_test.GoogleCallCredentialsTest",
   "unit._channel_args_test.ChannelArgsTest",
   "unit._channel_connectivity_test.ChannelConnectivityTest",
diff --git a/src/python/grpcio_tests/tests/unit/_auth_test.py b/src/python/grpcio_tests/tests/unit/_auth_test.py
index f61951b80a..e2cb938936 100644
--- a/src/python/grpcio_tests/tests/unit/_auth_test.py
+++ b/src/python/grpcio_tests/tests/unit/_auth_test.py
@@ -61,7 +61,7 @@ class GoogleCallCredentialsTest(unittest.TestCase):
         self.assertTrue(callback_event.wait(1.0))
 
 
-class AccessTokenCallCredentialsTest(unittest.TestCase):
+class AccessTokenAuthMetadataPluginTest(unittest.TestCase):
 
     def test_google_call_credentials_success(self):
         callback_event = threading.Event()
@@ -71,8 +71,8 @@ class AccessTokenCallCredentialsTest(unittest.TestCase):
             self.assertIsNone(error)
             callback_event.set()
 
-        call_creds = _auth.AccessTokenCallCredentials('token')
-        call_creds(None, mock_callback)
+        metadata_plugin = _auth.AccessTokenAuthMetadataPlugin('token')
+        metadata_plugin(None, mock_callback)
         self.assertTrue(callback_event.wait(1.0))
 
 
diff --git a/src/python/grpcio_tests/tests/unit/_cython/cygrpc_test.py b/src/python/grpcio_tests/tests/unit/_cython/cygrpc_test.py
index 18d4a6df64..da94cf8028 100644
--- a/src/python/grpcio_tests/tests/unit/_cython/cygrpc_test.py
+++ b/src/python/grpcio_tests/tests/unit/_cython/cygrpc_test.py
@@ -28,7 +28,7 @@ _CALL_CREDENTIALS_METADATA_VALUE = 'call-creds-value'
 _EMPTY_FLAGS = 0
 
 
-def _metadata_plugin_callback(context, callback):
+def _metadata_plugin(context, callback):
     callback(
         cygrpc.Metadata([
             cygrpc.Metadatum(_CALL_CREDENTIALS_METADATA_KEY,
@@ -105,17 +105,9 @@ class TypeSmokeTest(unittest.TestCase):
         channel = cygrpc.Channel(b'[::]:0', cygrpc.ChannelArgs([]))
         del channel
 
-    def testCredentialsMetadataPluginUpDown(self):
-        plugin = cygrpc.CredentialsMetadataPlugin(
-            lambda ignored_a, ignored_b: None, b'')
-        del plugin
-
-    def testCallCredentialsFromPluginUpDown(self):
-        plugin = cygrpc.CredentialsMetadataPlugin(_metadata_plugin_callback,
-                                                  b'')
-        call_credentials = cygrpc.call_credentials_metadata_plugin(plugin)
-        del plugin
-        del call_credentials
+    def test_metadata_plugin_call_credentials_up_down(self):
+        cygrpc.MetadataPluginCallCredentials(_metadata_plugin,
+                                             b'test plugin name!')
 
     def testServerStartNoExplicitShutdown(self):
         server = cygrpc.Server(cygrpc.ChannelArgs([]))
@@ -205,7 +197,7 @@ class ServerClientMixin(object):
 
         return test_utilities.SimpleFuture(performer)
 
-    def testEcho(self):
+    def test_echo(self):
         DEADLINE = time.time() + 5
         DEADLINE_TOLERANCE = 0.25
         CLIENT_METADATA_ASCII_KEY = b'key'
@@ -439,8 +431,8 @@ class SecureServerSecureClient(unittest.TestCase, ServerClientMixin):
             cygrpc.SslPemKeyCertPair(resources.private_key(),
                                      resources.certificate_chain())
         ], False)
-        client_credentials = cygrpc.channel_credentials_ssl(
-            resources.test_root_certificates(), None)
+        client_credentials = cygrpc.SSLChannelCredentials(
+            resources.test_root_certificates(), None, None)
         self.setUpMixin(server_credentials, client_credentials,
                         _SSL_HOST_OVERRIDE)
 
diff --git a/src/python/grpcio_tests/tests/unit/_invocation_defects_test.py b/src/python/grpcio_tests/tests/unit/_invocation_defects_test.py
index 0a1e50c94c..2a1a49ce74 100644
--- a/src/python/grpcio_tests/tests/unit/_invocation_defects_test.py
+++ b/src/python/grpcio_tests/tests/unit/_invocation_defects_test.py
@@ -32,6 +32,7 @@ _UNARY_UNARY = '/test/UnaryUnary'
 _UNARY_STREAM = '/test/UnaryStream'
 _STREAM_UNARY = '/test/StreamUnary'
 _STREAM_STREAM = '/test/StreamStream'
+_DEFECTIVE_GENERIC_RPC_HANDLER = '/test/DefectiveGenericRpcHandler'
 
 
 class _Callback(object):
@@ -95,6 +96,9 @@ class _Handler(object):
             yield request
         self._control.control()
 
+    def defective_generic_rpc_handler(self):
+        raise test_control.Defect()
+
 
 class _MethodHandler(grpc.RpcMethodHandler):
 
@@ -132,6 +136,8 @@ class _GenericHandler(grpc.GenericRpcHandler):
         elif handler_call_details.method == _STREAM_STREAM:
             return _MethodHandler(True, True, None, None, None, None, None,
                                   self._handler.handle_stream_stream)
+        elif handler_call_details.method == _DEFECTIVE_GENERIC_RPC_HANDLER:
+            return self._handler.defective_generic_rpc_handler()
         else:
             return None
 
@@ -176,6 +182,10 @@ def _stream_stream_multi_callable(channel):
     return channel.stream_stream(_STREAM_STREAM)
 
 
+def _defective_handler_multi_callable(channel):
+    return channel.unary_unary(_DEFECTIVE_GENERIC_RPC_HANDLER)
+
+
 class InvocationDefectsTest(unittest.TestCase):
 
     def setUp(self):
@@ -235,6 +245,18 @@ class InvocationDefectsTest(unittest.TestCase):
             for _ in range(test_constants.STREAM_LENGTH // 2 + 1):
                 next(response_iterator)
 
+    def testDefectiveGenericRpcHandlerUnaryResponse(self):
+        request = b'\x07\x08'
+        multi_callable = _defective_handler_multi_callable(self._channel)
+
+        with self.assertRaises(grpc.RpcError) as exception_context:
+            response = multi_callable(
+                request,
+                metadata=(('test', 'DefectiveGenericRpcHandlerUnary'),))
+
+        self.assertIs(grpc.StatusCode.UNKNOWN,
+                      exception_context.exception.code())
+
 
 if __name__ == '__main__':
     unittest.main(verbosity=2)
diff --git a/test/core/security/ssl_server_fuzzer.cc b/test/core/security/ssl_server_fuzzer.cc
index bbb2f6013e..d83ebb18d2 100644
--- a/test/core/security/ssl_server_fuzzer.cc
+++ b/test/core/security/ssl_server_fuzzer.cc
@@ -92,8 +92,9 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
   grpc_handshake_manager* handshake_mgr = grpc_handshake_manager_create();
   grpc_server_security_connector_add_handshakers(&exec_ctx, sc, handshake_mgr);
   grpc_handshake_manager_do_handshake(
-      &exec_ctx, handshake_mgr, mock_endpoint, nullptr /* channel_args */,
-      deadline, nullptr /* acceptor */, on_handshake_done, &state);
+      &exec_ctx, handshake_mgr, nullptr /* interested_parties */, mock_endpoint,
+      nullptr /* channel_args */, deadline, nullptr /* acceptor */,
+      on_handshake_done, &state);
   grpc_exec_ctx_flush(&exec_ctx);
 
   // If the given string happens to be part of the correct client hello, the
diff --git a/tools/run_tests/run_tests.py b/tools/run_tests/run_tests.py
index 766c1c0b7c..471f5d99e7 100755
--- a/tools/run_tests/run_tests.py
+++ b/tools/run_tests/run_tests.py
@@ -1231,7 +1231,7 @@ if not args.disable_auto_set_flakes:
       if test.flaky: flaky_tests.add(test.name)
       if test.cpu > 0: shortname_to_cpu[test.name] = test.cpu
   except:
-    print("Unexpected error getting flaky tests:", sys.exc_info()[0])
+    print("Unexpected error getting flaky tests: %s" % traceback.format_exc())
 
 if args.force_default_poller:
   _POLLING_STRATEGIES = {}