Merge branch 'master' into sreek-epoll1

24 files changed, 296 insertions, 153 deletions

diff --git a/.github/CODEOWNERS b/.github/CODEOWNERS
index 73c3609aa0..e4e7c47c5a 100644
--- a/.github/CODEOWNERS
+++ b/.github/CODEOWNERS
@@ -2,36 +2,40 @@
 # Uses OWNERS files in different modules throughout the
 # repository as the source of truth for module ownership.
 /** @a11r @nicolasnoble @ctiller
-/binding.gyp @murgatroid99
-/Gemfile @murgatroid99
-/grpc.gemspec @murgatroid99
-/package.json @murgatroid99
-/Rakefile @murgatroid99
+/*.podspec @muxi @makdharma @a11r @nicolasnoble @ctiller
+/binding.gyp @murgatroid99 @a11r @nicolasnoble @ctiller
+/Gemfile @murgatroid99 @a11r @nicolasnoble @ctiller
+/grpc.gemspec @murgatroid99 @a11r @nicolasnoble @ctiller
+/package.json @murgatroid99 @a11r @nicolasnoble @ctiller
+/Rakefile @murgatroid99 @a11r @nicolasnoble @ctiller
+/grpc.bzl @muxi @makdharma @a11r @nicolasnoble @ctiller
 /bazel/** @nicolasnoble @dgquintas @ctiller
 /cmake/** @jtattermusch @a11r @nicolasnoble @ctiller
 /doc/PROTOCOL-HTTP2.md @ejona86 @a11r @nicolasnoble @ctiller
 /doc/interop-test-descriptions.md @ejona86 @a11r @nicolasnoble @ctiller
 /etc/** @jboeuf @nicolasnoble @a11r @ctiller
 /examples/node/** @murgatroid99 @a11r @nicolasnoble @ctiller
+/examples/objective-c/** @muxi @makdharma @a11r @nicolasnoble @ctiller
+/examples/python/** @nathanielmanistaatgoogle @kpayson64 @mehrdada
 /include/** @ctiller @markdroth @dgquintas @a11r @nicolasnoble
-/src/core/** @ctiller @markdroth @dgquintas @a11r @nicolasnoble
-/src/core/lib/iomgr/*_uv.c @murgatroid99 @ctiller @markdroth @dgquintas @a11r @nicolasnoble
-/src/core/lib/iomgr/*_uv.h @murgatroid99 @ctiller @markdroth @dgquintas @a11r @nicolasnoble
-/src/cpp/** @ctiller @markdroth @dgquintas @a11r @nicolasnoble
+/src/core/** @ctiller @markdroth @dgquintas
+/src/core/lib/iomgr/*_uv.c @murgatroid99 @ctiller @markdroth @dgquintas
+/src/core/lib/iomgr/*_uv.h @murgatroid99 @ctiller @markdroth @dgquintas
+/src/cpp/** @ctiller @markdroth @dgquintas
 /src/csharp/** @jtattermusch @apolcyn @a11r @nicolasnoble @ctiller
 /src/node/** @murgatroid99 @a11r @nicolasnoble @ctiller
 /src/objective-c/** @muxi @makdharma @a11r @nicolasnoble @ctiller
 /src/php/** @stanley-cheung @murgatroid99 @a11r @nicolasnoble @ctiller
-/src/python/** @nathanielmanistaatgoogle @kpayson64 @a11r @nicolasnoble @ctiller
+/src/python/** @nathanielmanistaatgoogle @kpayson64 @mehrdada
+/src/python/grpcio/grpc_core_dependencies.py @a11y @ctiller @nicolasnoble @nathanielmanistaatgoogle @kpayson64 @mehrdada
 /src/ruby/** @apolcyn @murgatroid99 @a11r @nicolasnoble @ctiller
 /test/build/** @ctiller @markdroth @dgquintas @a11r @nicolasnoble
-/test/core/** @ctiller @markdroth @dgquintas @a11r @nicolasnoble
-/test/cpp/** @ctiller @markdroth @dgquintas @a11r @nicolasnoble
-/test/cpp/qps/** @vjpai @ctiller @markdroth @dgquintas @a11r @nicolasnoble
+/test/core/** @ctiller @markdroth @dgquintas
+/test/cpp/** @ctiller @markdroth @dgquintas
+/test/cpp/qps/** @vjpai @ctiller @markdroth @dgquintas
 /test/distrib/node/** @murgatroid99 @a11r @nicolasnoble @ctiller
 /tools/** @matt-kwong @jtattermusch @nicolasnoble @a11r @ctiller
 /tools/codegen/core/** @ctiller @dgquintas @markdroth
-/tools/dockerfile/** @matt-kwong @jtattermusch @nicolasnoble @a11r @ctiller
-/tools/run_tests/** @matt-kwong @jtattermusch @nicolasnoble @a11r @ctiller
+/tools/distrib/python/** @nathanielmanistaatgoogle @kpayson64 @mehrdada
 /tools/run_tests/artifacts/*_node* @murgatroid99 @matt-kwong @jtattermusch @nicolasnoble @a11r @ctiller
 /tools/run_tests/helper_scripts/*_node* @murgatroid99 @matt-kwong @jtattermusch @nicolasnoble @a11r @ctiller
diff --git a/OWNERS b/OWNERS
index 87958a4566..7e6a84c57a 100644
--- a/OWNERS
+++ b/OWNERS
@@ -5,3 +5,5 @@
 @ctiller
 
 @murgatroid99 binding.gyp Gemfile grpc.gemspec package.json Rakefile
+@muxi *.podspec grpc.bzl
+@makdharma *.podspec grpc.bzl
diff --git a/examples/objective-c/OWNERS b/examples/objective-c/OWNERS
new file mode 100644
index 0000000000..c14fe53c06
--- /dev/null
+++ b/examples/objective-c/OWNERS
@@ -0,0 +1,2 @@
+@muxi
+@makdharma
diff --git a/examples/python/OWNERS b/examples/python/OWNERS
new file mode 100644
index 0000000000..ea3909e0a3
--- /dev/null
+++ b/examples/python/OWNERS
@@ -0,0 +1,5 @@
+set noparent
+
+@nathanielmanistaatgoogle
+@kpayson64
+@mehrdada
diff --git a/src/core/OWNERS b/src/core/OWNERS
index 8dca75ce91..986c9a1c3c 100644
--- a/src/core/OWNERS
+++ b/src/core/OWNERS
@@ -1,3 +1,4 @@
+set noparent
 @ctiller
 @markdroth
 @dgquintas
diff --git a/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.c b/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.c
index 37580087a7..341763a4d7 100644
--- a/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.c
+++ b/src/core/ext/filters/client_channel/lb_policy/round_robin/round_robin.c
@@ -142,6 +142,21 @@ struct rr_subchannel_list {
   bool shutting_down;
 };
 
+static rr_subchannel_list *rr_subchannel_list_create(round_robin_lb_policy *p,
+                                                     size_t num_subchannels) {
+  rr_subchannel_list *subchannel_list = gpr_zalloc(sizeof(*subchannel_list));
+  subchannel_list->policy = p;
+  subchannel_list->subchannels =
+      gpr_zalloc(sizeof(subchannel_data) * num_subchannels);
+  subchannel_list->num_subchannels = num_subchannels;
+  gpr_ref_init(&subchannel_list->refcount, 1);
+  if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
+    gpr_log(GPR_INFO, "[RR %p] Created subchannel list %p for %lu subchannels",
+            (void *)p, (void *)subchannel_list, (unsigned long)num_subchannels);
+  }
+  return subchannel_list;
+}
+
 static void rr_subchannel_list_destroy(grpc_exec_ctx *exec_ctx,
                                        rr_subchannel_list *subchannel_list) {
   GPR_ASSERT(subchannel_list->shutting_down);
@@ -171,9 +186,9 @@ static void rr_subchannel_list_ref(rr_subchannel_list *subchannel_list,
   gpr_ref_non_zero(&subchannel_list->refcount);
   if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
     const gpr_atm count = gpr_atm_acq_load(&subchannel_list->refcount.count);
-    gpr_log(GPR_INFO, "[RR %p] subchannel_list %p REF %lu->%lu",
+    gpr_log(GPR_INFO, "[RR %p] subchannel_list %p REF %lu->%lu (%s)",
             (void *)subchannel_list->policy, (void *)subchannel_list,
-            (unsigned long)(count - 1), (unsigned long)count);
+            (unsigned long)(count - 1), (unsigned long)count, reason);
   }
 }
 
@@ -183,9 +198,9 @@ static void rr_subchannel_list_unref(grpc_exec_ctx *exec_ctx,
   const bool done = gpr_unref(&subchannel_list->refcount);
   if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
     const gpr_atm count = gpr_atm_acq_load(&subchannel_list->refcount.count);
-    gpr_log(GPR_INFO, "[RR %p] subchannel_list %p UNREF %lu->%lu",
+    gpr_log(GPR_INFO, "[RR %p] subchannel_list %p UNREF %lu->%lu (%s)",
             (void *)subchannel_list->policy, (void *)subchannel_list,
-            (unsigned long)(count + 1), (unsigned long)count);
+            (unsigned long)(count + 1), (unsigned long)count, reason);
   }
   if (done) {
     rr_subchannel_list_destroy(exec_ctx, subchannel_list);
@@ -194,19 +209,13 @@ static void rr_subchannel_list_unref(grpc_exec_ctx *exec_ctx,
 
 /** Mark \a subchannel_list as discarded. Unsubscribes all its subchannels. The
  * watcher's callback will ultimately unref \a subchannel_list.  */
-static void rr_subchannel_list_shutdown(grpc_exec_ctx *exec_ctx,
-                                        rr_subchannel_list *subchannel_list,
-                                        const char *reason) {
-  if (subchannel_list->shutting_down) {
-    if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
-      gpr_log(GPR_DEBUG, "Subchannel list %p already shutting down",
-              (void *)subchannel_list);
-    }
-    return;
-  };
+static void rr_subchannel_list_shutdown_and_unref(
+    grpc_exec_ctx *exec_ctx, rr_subchannel_list *subchannel_list,
+    const char *reason) {
+  GPR_ASSERT(!subchannel_list->shutting_down);
   if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
-    gpr_log(GPR_DEBUG, "Shutting down subchannel_list %p",
-            (void *)subchannel_list);
+    gpr_log(GPR_DEBUG, "[RR %p] Shutting down subchannel_list %p (%s)",
+            (void *)subchannel_list->policy, (void *)subchannel_list, reason);
   }
   GPR_ASSERT(!subchannel_list->shutting_down);
   subchannel_list->shutting_down = true;
@@ -214,10 +223,12 @@ static void rr_subchannel_list_shutdown(grpc_exec_ctx *exec_ctx,
     subchannel_data *sd = &subchannel_list->subchannels[i];
     if (sd->subchannel != NULL) {  // if subchannel isn't shutdown, unsubscribe.
       if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
-        gpr_log(GPR_DEBUG,
-                "Unsubscribing from subchannel %p as part of shutting down "
-                "subchannel_list %p",
-                (void *)sd->subchannel, (void *)subchannel_list);
+        gpr_log(
+            GPR_DEBUG,
+            "[RR %p] Unsubscribing from subchannel %p as part of shutting down "
+            "subchannel_list %p",
+            (void *)subchannel_list->policy, (void *)sd->subchannel,
+            (void *)subchannel_list);
       }
       grpc_subchannel_notify_on_state_change(exec_ctx, sd->subchannel, NULL,
                                              NULL,
@@ -294,7 +305,8 @@ static void update_last_ready_subchannel_index_locked(round_robin_lb_policy *p,
 static void rr_destroy(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
   round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
   if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
-    gpr_log(GPR_DEBUG, "Destroying Round Robin policy at %p", (void *)pol);
+    gpr_log(GPR_DEBUG, "[RR %p] Destroying Round Robin policy at %p",
+            (void *)pol, (void *)pol);
   }
   grpc_connectivity_state_destroy(exec_ctx, &p->state_tracker);
   gpr_free(p);
@@ -303,7 +315,8 @@ static void rr_destroy(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
 static void rr_shutdown_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
   round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
   if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
-    gpr_log(GPR_DEBUG, "Shutting down Round Robin policy at %p", (void *)pol);
+    gpr_log(GPR_DEBUG, "[RR %p] Shutting down Round Robin policy at %p",
+            (void *)pol, (void *)pol);
   }
   p->shutdown = true;
   pending_pick *pp;
@@ -318,9 +331,18 @@ static void rr_shutdown_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
   grpc_connectivity_state_set(
       exec_ctx, &p->state_tracker, GRPC_CHANNEL_SHUTDOWN,
       GRPC_ERROR_CREATE_FROM_STATIC_STRING("Channel Shutdown"), "rr_shutdown");
-  rr_subchannel_list_shutdown(exec_ctx, p->subchannel_list,
-                              "sl_shutdown_rr_shutdown");
+  const bool latest_is_current =
+      p->subchannel_list == p->latest_pending_subchannel_list;
+  rr_subchannel_list_shutdown_and_unref(exec_ctx, p->subchannel_list,
+                                        "sl_shutdown_rr_shutdown");
   p->subchannel_list = NULL;
+  if (!latest_is_current && p->latest_pending_subchannel_list != NULL &&
+      !p->latest_pending_subchannel_list->shutting_down) {
+    rr_subchannel_list_shutdown_and_unref(exec_ctx,
+                                          p->latest_pending_subchannel_list,
+                                          "sl_shutdown_pending_rr_shutdown");
+    p->latest_pending_subchannel_list = NULL;
+  }
 }
 
 static void rr_cancel_pick_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
@@ -376,8 +398,8 @@ static void start_picking_locked(grpc_exec_ctx *exec_ctx,
   p->started_picking = true;
   for (size_t i = 0; i < p->subchannel_list->num_subchannels; i++) {
     subchannel_data *sd = &p->subchannel_list->subchannels[i];
-    GRPC_LB_POLICY_WEAK_REF(&p->base, "rr_connectivity");
-    rr_subchannel_list_ref(sd->subchannel_list, "start_picking");
+    GRPC_LB_POLICY_WEAK_REF(&p->base, "start_picking_locked");
+    rr_subchannel_list_ref(sd->subchannel_list, "started_picking");
     grpc_subchannel_notify_on_state_change(
         exec_ctx, sd->subchannel, p->base.interested_parties,
         &sd->pending_connectivity_state_unsafe,
@@ -399,7 +421,7 @@ static int rr_pick_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
                           grpc_closure *on_complete) {
   round_robin_lb_policy *p = (round_robin_lb_policy *)pol;
   if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
-    gpr_log(GPR_INFO, "Round Robin %p trying to pick", (void *)pol);
+    gpr_log(GPR_INFO, "[RR %p] Trying to pick", (void *)pol);
   }
   if (p->subchannel_list != NULL) {
     const size_t next_ready_index = get_next_ready_subchannel_index_locked(p);
@@ -415,8 +437,8 @@ static int rr_pick_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol,
       if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
         gpr_log(
             GPR_DEBUG,
-            "[RR %p] PICKED TARGET <-- SUBCHANNEL %p (CONNECTED %p) (SL %p, "
-            "INDEX %lu)",
+            "[RR %p] Picked target <-- Subchannel %p (connected %p) (sl %p, "
+            "index %lu)",
             (void *)p, (void *)sd->subchannel, (void *)*target,
             (void *)sd->subchannel_list, (unsigned long)next_ready_index);
       }
@@ -545,22 +567,27 @@ static void rr_connectivity_changed_locked(grpc_exec_ctx *exec_ctx, void *arg,
   }
   // If the policy is shutting down, unref and return.
   if (p->shutdown) {
-    rr_subchannel_list_unref(exec_ctx, sd->subchannel_list, "pol_shutdown");
+    rr_subchannel_list_unref(exec_ctx, sd->subchannel_list,
+                             "pol_shutdown+started_picking");
     GRPC_LB_POLICY_WEAK_UNREF(exec_ctx, &p->base, "pol_shutdown");
     return;
   }
   if (sd->subchannel_list->shutting_down && error == GRPC_ERROR_CANCELLED) {
     // the subchannel list associated with sd has been discarded. This callback
-    // corresponds to the unsubscription.
-    rr_subchannel_list_unref(exec_ctx, sd->subchannel_list, "sl_shutdown");
-    GRPC_LB_POLICY_WEAK_UNREF(exec_ctx, &p->base, "sl_shutdown");
+    // corresponds to the unsubscription. The unrefs correspond to the picking
+    // ref (start_picking_locked or update_started_picking).
+    rr_subchannel_list_unref(exec_ctx, sd->subchannel_list,
+                             "sl_shutdown+started_picking");
+    GRPC_LB_POLICY_WEAK_UNREF(exec_ctx, &p->base, "sl_shutdown+picking");
     return;
   }
   // Dispose of outdated subchannel lists.
   if (sd->subchannel_list != p->subchannel_list &&
       sd->subchannel_list != p->latest_pending_subchannel_list) {
     // sd belongs to an outdated subchannel_list: get rid of it.
-    rr_subchannel_list_shutdown(exec_ctx, sd->subchannel_list, "sl_oudated");
+    rr_subchannel_list_shutdown_and_unref(exec_ctx, sd->subchannel_list,
+                                          "sl_outdated");
+    GRPC_LB_POLICY_WEAK_UNREF(exec_ctx, &p->base, "sl_outdated");
     return;
   }
   // Now that we're inside the combiner, copy the pending connectivity
@@ -583,7 +610,7 @@ static void rr_connectivity_changed_locked(grpc_exec_ctx *exec_ctx, void *arg,
       sd->user_data = NULL;
     }
     if (new_policy_connectivity_state == GRPC_CHANNEL_SHUTDOWN) {
-      /* the policy is shutting down. Flush all the pending picks... */
+      // the policy is shutting down. Flush all the pending picks...
       pending_pick *pp;
       while ((pp = p->pending_picks)) {
         p->pending_picks = pp->next;
@@ -592,8 +619,9 @@ static void rr_connectivity_changed_locked(grpc_exec_ctx *exec_ctx, void *arg,
         gpr_free(pp);
       }
     }
-    /* unref the "rr_connectivity" weak ref from start_picking */
-    rr_subchannel_list_unref(exec_ctx, sd->subchannel_list, "sd_shutdown");
+    rr_subchannel_list_unref(exec_ctx, sd->subchannel_list,
+                             "sd_shutdown+started_picking");
+    // unref the "rr_connectivity_update" weak ref from start_picking.
     GRPC_LB_POLICY_WEAK_UNREF(exec_ctx, &p->base,
                               "rr_connectivity_sd_shutdown");
   } else {  // sd not in SHUTDOWN
@@ -618,10 +646,10 @@ static void rr_connectivity_changed_locked(grpc_exec_ctx *exec_ctx, void *arg,
         }
         if (p->subchannel_list != NULL) {
           // dispose of the current subchannel_list
-          rr_subchannel_list_shutdown(exec_ctx, p->subchannel_list,
-                                      "sl_shutdown_rr_update_connectivity");
+          rr_subchannel_list_shutdown_and_unref(exec_ctx, p->subchannel_list,
+                                                "sl_phase_out_shutdown");
         }
-        p->subchannel_list = sd->subchannel_list;
+        p->subchannel_list = p->latest_pending_subchannel_list;
         p->latest_pending_subchannel_list = NULL;
       }
       /* at this point we know there's at least one suitable subchannel. Go
@@ -632,8 +660,8 @@ static void rr_connectivity_changed_locked(grpc_exec_ctx *exec_ctx, void *arg,
       subchannel_data *selected =
           &p->subchannel_list->subchannels[next_ready_index];
       if (p->pending_picks != NULL) {
-        /* if the selected subchannel is going to be used for the pending
-         * picks, update the last picked pointer */
+        // if the selected subchannel is going to be used for the pending
+        // picks, update the last picked pointer
         update_last_ready_subchannel_index_locked(p, next_ready_index);
       }
       pending_pick *pp;
@@ -647,16 +675,17 @@ static void rr_connectivity_changed_locked(grpc_exec_ctx *exec_ctx, void *arg,
         }
         if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
           gpr_log(GPR_DEBUG,
-                  "[RR CONN CHANGED] TARGET <-- SUBCHANNEL %p (INDEX %lu)",
-                  (void *)selected->subchannel,
-                  (unsigned long)next_ready_index);
+                  "[RR %p] Fulfilling pending pick. Target <-- subchannel %p "
+                  "(subchannel_list %p, index %lu)",
+                  (void *)p, (void *)selected->subchannel,
+                  (void *)p->subchannel_list, (unsigned long)next_ready_index);
         }
         GRPC_CLOSURE_SCHED(exec_ctx, pp->on_complete, GRPC_ERROR_NONE);
         gpr_free(pp);
       }
     }
-    /* renew notification: reuses the "rr_connectivity" weak ref on the policy
-     * as well as the sd->subchannel_list ref. */
+    /* renew notification: reuses the "rr_connectivity_update" weak ref on the
+     * policy as well as the sd->subchannel_list ref. */
     grpc_subchannel_notify_on_state_change(
         exec_ctx, sd->subchannel, p->base.interested_parties,
         &sd->pending_connectivity_state_unsafe,
@@ -714,8 +743,7 @@ static void rr_update_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
     } else {
       // otherwise, keep using the current subchannel list (ignore this update).
       gpr_log(GPR_ERROR,
-              "No valid LB addresses channel arg for Round Robin %p update, "
-              "ignoring.",
+              "[RR %p] No valid LB addresses channel arg for update, ignoring.",
               (void *)p);
     }
     return;
@@ -731,24 +759,27 @@ static void rr_update_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
         GRPC_ERROR_CREATE_FROM_STATIC_STRING("Empty update"),
         "rr_update_empty");
     if (p->subchannel_list != NULL) {
-      rr_subchannel_list_shutdown(exec_ctx, p->subchannel_list,
-                                  "sl_shutdown_rr_update");
+      rr_subchannel_list_shutdown_and_unref(exec_ctx, p->subchannel_list,
+                                            "sl_shutdown_empty_update");
       p->subchannel_list = NULL;
     }
     return;
   }
   size_t subchannel_index = 0;
-  rr_subchannel_list *subchannel_list = gpr_zalloc(sizeof(*subchannel_list));
-  subchannel_list->policy = p;
-  subchannel_list->subchannels =
-      gpr_zalloc(sizeof(subchannel_data) * num_addrs);
-  subchannel_list->num_subchannels = num_addrs;
-  gpr_ref_init(&subchannel_list->refcount, 1);
-  p->latest_pending_subchannel_list = subchannel_list;
-  if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
-    gpr_log(GPR_DEBUG, "Created subchannel list %p for %lu subchannels",
-            (void *)subchannel_list, (unsigned long)num_addrs);
+  rr_subchannel_list *subchannel_list = rr_subchannel_list_create(p, num_addrs);
+  if (p->latest_pending_subchannel_list != NULL && p->started_picking) {
+    if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
+      gpr_log(GPR_DEBUG,
+              "[RR %p] Shutting down latest pending subchannel list %p, about "
+              "to be "
+              "replaced by newer latest %p",
+              (void *)p, (void *)p->latest_pending_subchannel_list,
+              (void *)subchannel_list);
+    }
+    rr_subchannel_list_shutdown_and_unref(
+        exec_ctx, p->latest_pending_subchannel_list, "sl_outdated_dont_smash");
   }
+  p->latest_pending_subchannel_list = subchannel_list;
   grpc_subchannel_args sc_args;
   /* We need to remove the LB addresses in order to be able to compare the
    * subchannel keys of subchannels from a different batch of addresses. */
@@ -772,11 +803,12 @@ static void rr_update_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
     if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
       char *address_uri =
           grpc_sockaddr_to_uri(&addresses->addresses[i].address);
-      gpr_log(GPR_DEBUG,
-              "index %lu: Created subchannel %p for address uri %s into "
-              "subchannel_list %p",
-              (unsigned long)subchannel_index, (void *)subchannel, address_uri,
-              (void *)subchannel_list);
+      gpr_log(
+          GPR_DEBUG,
+          "[RR %p] index %lu: Created subchannel %p for address uri %s into "
+          "subchannel_list %p",
+          (void *)p, (unsigned long)subchannel_index, (void *)subchannel,
+          address_uri, (void *)subchannel_list);
       gpr_free(address_uri);
     }
     grpc_channel_args_destroy(exec_ctx, new_args);
@@ -815,10 +847,11 @@ static void rr_update_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
     // The policy isn't picking yet. Save the update for later, disposing of
     // previous version if any.
     if (p->subchannel_list != NULL) {
-      rr_subchannel_list_shutdown(exec_ctx, p->subchannel_list,
-                                  "rr_update_before_started_picking");
+      rr_subchannel_list_shutdown_and_unref(exec_ctx, p->subchannel_list,
+                                            "rr_update_before_started_picking");
     }
     p->subchannel_list = subchannel_list;
+    p->latest_pending_subchannel_list = NULL;
   }
 }
 
@@ -848,7 +881,7 @@ static grpc_lb_policy *round_robin_create(grpc_exec_ctx *exec_ctx,
   grpc_connectivity_state_init(&p->state_tracker, GRPC_CHANNEL_IDLE,
                                "round_robin");
   if (GRPC_TRACER_ON(grpc_lb_round_robin_trace)) {
-    gpr_log(GPR_DEBUG, "Created Round Robin %p with %lu subchannels", (void *)p,
+    gpr_log(GPR_DEBUG, "[RR %p] Created with %lu subchannels", (void *)p,
             (unsigned long)p->subchannel_list->num_subchannels);
   }
   return &p->base;
diff --git a/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.c b/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.c
index 244b260dfa..9065e33613 100644
--- a/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.c
+++ b/src/core/ext/filters/client_channel/resolver/dns/c_ares/grpc_ares_wrapper.c
@@ -236,12 +236,12 @@ static void on_srv_query_done_cb(void *arg, int status, int timeouts,
            srv_it = srv_it->next) {
         if (grpc_ipv6_loopback_available()) {
           grpc_ares_hostbyname_request *hr = create_hostbyname_request(
-              r, srv_it->host, srv_it->port, true /* is_balancer */);
+              r, srv_it->host, htons(srv_it->port), true /* is_balancer */);
           ares_gethostbyname(*channel, hr->host, AF_INET6,
                              on_hostbyname_done_cb, hr);
         }
         grpc_ares_hostbyname_request *hr = create_hostbyname_request(
-            r, srv_it->host, srv_it->port, true /* is_balancer */);
+            r, srv_it->host, htons(srv_it->port), true /* is_balancer */);
         ares_gethostbyname(*channel, hr->host, AF_INET, on_hostbyname_done_cb,
                            hr);
         grpc_ares_ev_driver_start(&exec_ctx, r->ev_driver);
diff --git a/src/core/ext/filters/client_channel/subchannel_index.c b/src/core/ext/filters/client_channel/subchannel_index.c
index e291ca9db9..a33ab950bf 100644
--- a/src/core/ext/filters/client_channel/subchannel_index.c
+++ b/src/core/ext/filters/client_channel/subchannel_index.c
@@ -40,6 +40,8 @@ struct grpc_subchannel_key {
 
 GPR_TLS_DECL(subchannel_index_exec_ctx);
 
+static bool g_force_creation = false;
+
 static void enter_ctx(grpc_exec_ctx *exec_ctx) {
   GPR_ASSERT(gpr_tls_get(&subchannel_index_exec_ctx) == 0);
   gpr_tls_set(&subchannel_index_exec_ctx, (intptr_t)exec_ctx);
@@ -84,6 +86,7 @@ static grpc_subchannel_key *subchannel_key_copy(grpc_subchannel_key *k) {
 
 int grpc_subchannel_key_compare(const grpc_subchannel_key *a,
                                 const grpc_subchannel_key *b) {
+  if (g_force_creation) return false;
   int c = GPR_ICMP(a->args.filter_count, b->args.filter_count);
   if (c != 0) return c;
   if (a->args.filter_count > 0) {
@@ -250,3 +253,7 @@ void grpc_subchannel_index_unregister(grpc_exec_ctx *exec_ctx,
 
   leave_ctx(exec_ctx);
 }
+
+void grpc_subchannel_index_test_only_set_force_creation(bool force_creation) {
+  g_force_creation = force_creation;
+}
diff --git a/src/core/ext/filters/client_channel/subchannel_index.h b/src/core/ext/filters/client_channel/subchannel_index.h
index e303bfaa05..98d882a453 100644
--- a/src/core/ext/filters/client_channel/subchannel_index.h
+++ b/src/core/ext/filters/client_channel/subchannel_index.h
@@ -59,4 +59,16 @@ void grpc_subchannel_index_init(void);
 /** Shutdown the subchannel index (global) */
 void grpc_subchannel_index_shutdown(void);
 
+/** \em TEST ONLY.
+ * If \a force_creation is true, all key comparisons will be false, resulting in
+ * new subchannels always being created. Otherwise, the keys will be compared as
+ * usual.
+ *
+ * This function is *not* threadsafe on purpose: it should *only* be used in
+ * test code.
+ *
+ * Tests using this function \em MUST run tests with and without \a
+ * force_creation set. */
+void grpc_subchannel_index_test_only_set_force_creation(bool force_creation);
+
 #endif /* GRPC_CORE_EXT_FILTERS_CLIENT_CHANNEL_SUBCHANNEL_INDEX_H */
diff --git a/src/core/lib/iomgr/ev_posix.c b/src/core/lib/iomgr/ev_posix.c
index a5ae04cb5b..cff77e641c 100644
--- a/src/core/lib/iomgr/ev_posix.c
+++ b/src/core/lib/iomgr/ev_posix.c
@@ -121,6 +121,10 @@ void grpc_set_event_engine_test_only(
   g_event_engine = ev_engine;
 }
 
+const grpc_event_engine_vtable *grpc_get_event_engine_test_only() {
+  return g_event_engine;
+}
+
 /* Call this only after calling grpc_event_engine_init() */
 const char *grpc_get_poll_strategy_name() { return g_poll_strategy_name; }
 
diff --git a/src/core/lib/iomgr/ev_posix.h b/src/core/lib/iomgr/ev_posix.h
index 54c4f2ee11..0de7333843 100644
--- a/src/core/lib/iomgr/ev_posix.h
+++ b/src/core/lib/iomgr/ev_posix.h
@@ -153,7 +153,9 @@ void grpc_pollset_set_del_fd(grpc_exec_ctx *exec_ctx,
 typedef int (*grpc_poll_function_type)(struct pollfd *, nfds_t, int);
 extern grpc_poll_function_type grpc_poll_function;
 
-/* This should be used for testing purposes ONLY */
+/* WARNING: The following two functions should be used for testing purposes
+ * ONLY */
 void grpc_set_event_engine_test_only(const grpc_event_engine_vtable *);
+const grpc_event_engine_vtable *grpc_get_event_engine_test_only();
 
 #endif /* GRPC_CORE_LIB_IOMGR_EV_POSIX_H */
diff --git a/src/core/lib/iomgr/timer_manager.c b/src/core/lib/iomgr/timer_manager.c
index b9bea9a2ab..631f7935d9 100644
--- a/src/core/lib/iomgr/timer_manager.c
+++ b/src/core/lib/iomgr/timer_manager.c
@@ -84,7 +84,14 @@ static void start_timer_thread_and_unlock(void) {
   gpr_thd_options opt = gpr_thd_options_default();
   gpr_thd_options_set_joinable(&opt);
   completed_thread *ct = gpr_malloc(sizeof(*ct));
+  // The call to gpr_thd_new() has to be under the same lock used by
+  // gc_completed_threads(), particularly due to ct->t, which is written here
+  // (internally by gpr_thd_new) and read there. Otherwise it's possible for ct
+  // to leak through g_completed_threads and be freed in gc_completed_threads()
+  // before "&ct->t" is written to, causing a use-after-free.
+  gpr_mu_lock(&g_mu);
   gpr_thd_new(&ct->t, timer_thread, ct, &opt);
+  gpr_mu_unlock(&g_mu);
 }
 
 void grpc_timer_manager_tick() {
diff --git a/src/cpp/OWNERS b/src/cpp/OWNERS
index 8dca75ce91..986c9a1c3c 100644
--- a/src/cpp/OWNERS
+++ b/src/cpp/OWNERS
@@ -1,3 +1,4 @@
+set noparent
 @ctiller
 @markdroth
 @dgquintas
diff --git a/src/python/OWNERS b/src/python/OWNERS
index 73a707c67d..ea3909e0a3 100644
--- a/src/python/OWNERS
+++ b/src/python/OWNERS
@@ -1,3 +1,5 @@
+set noparent
+
 @nathanielmanistaatgoogle
 @kpayson64
-
+@mehrdada
diff --git a/src/python/grpcio/OWNERS b/src/python/grpcio/OWNERS
new file mode 100644
index 0000000000..78d54ec96b
--- /dev/null
+++ b/src/python/grpcio/OWNERS
@@ -0,0 +1,3 @@
+@a11y grpc_core_dependencies.py
+@ctiller grpc_core_dependencies.py
+@nicolasnoble grpc_core_dependencies.py
diff --git a/test/core/OWNERS b/test/core/OWNERS
index 8dca75ce91..986c9a1c3c 100644
--- a/test/core/OWNERS
+++ b/test/core/OWNERS
@@ -1,3 +1,4 @@
+set noparent
 @ctiller
 @markdroth
 @dgquintas
diff --git a/test/cpp/OWNERS b/test/cpp/OWNERS
index 8dca75ce91..986c9a1c3c 100644
--- a/test/cpp/OWNERS
+++ b/test/cpp/OWNERS
@@ -1,3 +1,4 @@
+set noparent
 @ctiller
 @markdroth
 @dgquintas
diff --git a/test/cpp/end2end/client_lb_end2end_test.cc b/test/cpp/end2end/client_lb_end2end_test.cc
index 6d3f5a9d46..e1160ecdc6 100644
--- a/test/cpp/end2end/client_lb_end2end_test.cc
+++ b/test/cpp/end2end/client_lb_end2end_test.cc
@@ -35,6 +35,7 @@
 
 extern "C" {
 #include "src/core/ext/filters/client_channel/resolver/fake/fake_resolver.h"
+#include "src/core/ext/filters/client_channel/subchannel_index.h"
 }
 
 #include "src/proto/grpc/testing/echo.grpc.pb.h"
@@ -331,10 +332,14 @@ TEST_F(ClientLbEnd2endTest, PickFirstManyUpdates) {
   for (size_t i = 0; i < servers_.size(); ++i) {
     ports.emplace_back(servers_[i]->port_);
   }
-  for (size_t i = 0; i < 1000; ++i) {
-    std::random_shuffle(ports.begin(), ports.end());
-    SetNextResolution(ports);
-    if (i % 10 == 0) SendRpc();
+  for (const bool force_creation : {true, false}) {
+    grpc_subchannel_index_test_only_set_force_creation(force_creation);
+    gpr_log(GPR_INFO, "Force subchannel creation: %d", force_creation);
+    for (size_t i = 0; i < 1000; ++i) {
+      std::random_shuffle(ports.begin(), ports.end());
+      SetNextResolution(ports);
+      if (i % 10 == 0) SendRpc();
+    }
   }
   // Check LB policy name for the channel.
   EXPECT_EQ("pick_first", channel_->GetLoadBalancingPolicyName());
diff --git a/test/cpp/end2end/grpclb_end2end_test.cc b/test/cpp/end2end/grpclb_end2end_test.cc
index a8ac631fbd..86cce2d30d 100644
--- a/test/cpp/end2end/grpclb_end2end_test.cc
+++ b/test/cpp/end2end/grpclb_end2end_test.cc
@@ -195,12 +195,13 @@ class BalancerServiceImpl : public BalancerService {
     for (const auto& response_and_delay : responses_and_delays) {
       {
         std::unique_lock<std::mutex> lock(mu_);
-        if (shutdown_) break;
+        if (shutdown_) goto done;
       }
       SendResponse(stream, response_and_delay.first, response_and_delay.second);
     }
     {
       std::unique_lock<std::mutex> lock(mu_);
+      if (shutdown_) goto done;
       serverlist_cond_.wait(lock);
     }
 
@@ -210,6 +211,9 @@ class BalancerServiceImpl : public BalancerService {
       gpr_log(GPR_INFO, "LB: recv client load report msg: '%s'",
               request.DebugString().c_str());
       GPR_ASSERT(request.has_client_stats());
+      // We need to acquire the lock here in order to prevent the notify_one
+      // below from firing before its corresponding wait is executed.
+      std::lock_guard<std::mutex> lock(mu_);
       client_stats_.num_calls_started +=
           request.client_stats().num_calls_started();
       client_stats_.num_calls_finished +=
@@ -225,10 +229,9 @@ class BalancerServiceImpl : public BalancerService {
               .num_calls_finished_with_client_failed_to_send();
       client_stats_.num_calls_finished_known_received +=
           request.client_stats().num_calls_finished_known_received();
-      std::lock_guard<std::mutex> lock(mu_);
       load_report_cond_.notify_one();
     }
-
+  done:
     gpr_log(GPR_INFO, "LB: done");
     return Status::OK;
   }
@@ -429,19 +432,24 @@ class GrpclbEnd2endTest : public ::testing::Test {
     explicit ServerThread(const grpc::string& type,
                           const grpc::string& server_host, T* service)
         : type_(type), service_(service) {
+      std::mutex mu;
+      // We need to acquire the lock here in order to prevent the notify_one
+      // by ServerThread::Start from firing before the wait below is hit.
+      std::unique_lock<std::mutex> lock(mu);
       port_ = grpc_pick_unused_port_or_die();
       gpr_log(GPR_INFO, "starting %s server on port %d", type_.c_str(), port_);
-      std::mutex mu;
       std::condition_variable cond;
       thread_.reset(new std::thread(
           std::bind(&ServerThread::Start, this, server_host, &mu, &cond)));
-      std::unique_lock<std::mutex> lock(mu);
       cond.wait(lock);
       gpr_log(GPR_INFO, "%s server startup complete", type_.c_str());
     }
 
     void Start(const grpc::string& server_host, std::mutex* mu,
                std::condition_variable* cond) {
+      // We need to acquire the lock here in order to prevent the notify_one
+      // below from firing before its corresponding wait is executed.
+      std::lock_guard<std::mutex> lock(*mu);
       std::ostringstream server_address;
       server_address << server_host << ":" << port_;
       ServerBuilder builder;
@@ -449,13 +457,12 @@ class GrpclbEnd2endTest : public ::testing::Test {
                                InsecureServerCredentials());
       builder.RegisterService(service_);
       server_ = builder.BuildAndStart();
-      std::lock_guard<std::mutex> lock(*mu);
       cond->notify_one();
     }
 
     void Shutdown() {
       gpr_log(GPR_INFO, "%s about to shutdown", type_.c_str());
-      server_->Shutdown();
+      server_->Shutdown(grpc_timeout_milliseconds_to_deadline(0));
       thread_->join();
       gpr_log(GPR_INFO, "%s shutdown completed", type_.c_str());
     }
@@ -821,6 +828,7 @@ TEST_F(UpdatesTest, UpdateBalancersDeadUpdate) {
 
   // Kill balancer 0
   gpr_log(GPR_INFO, "********** ABOUT TO KILL BALANCER 0 *************");
+  balancers_[0]->NotifyDoneWithServerlists();
   if (balancers_[0]->Shutdown()) balancer_servers_[0].Shutdown();
   gpr_log(GPR_INFO, "********** KILLED BALANCER 0 *************");
 
diff --git a/test/cpp/microbenchmarks/bm_cq_multiple_threads.cc b/test/cpp/microbenchmarks/bm_cq_multiple_threads.cc
index 1e3830a556..f79db15a47 100644
--- a/test/cpp/microbenchmarks/bm_cq_multiple_threads.cc
+++ b/test/cpp/microbenchmarks/bm_cq_multiple_threads.cc
@@ -41,6 +41,7 @@ namespace testing {
 static void* g_tag = (void*)(intptr_t)10;  // Some random number
 static grpc_completion_queue* g_cq;
 static grpc_event_engine_vtable g_vtable;
+static const grpc_event_engine_vtable* g_old_vtable;
 
 static void pollset_shutdown(grpc_exec_ctx* exec_ctx, grpc_pollset* ps,
                              grpc_closure* closure) {
@@ -72,7 +73,7 @@ static grpc_error* pollset_work(grpc_exec_ctx* exec_ctx, grpc_pollset* ps,
                                 grpc_pollset_worker** worker, gpr_timespec now,
                                 gpr_timespec deadline) {
   if (gpr_time_cmp(deadline, gpr_time_0(GPR_CLOCK_MONOTONIC)) == 0) {
-    gpr_log(GPR_ERROR, "no-op");
+    gpr_log(GPR_DEBUG, "no-op");
     return GRPC_ERROR_NONE;
   }
 
@@ -98,7 +99,12 @@ static void init_engine_vtable() {
 
 static void setup() {
   grpc_init();
+
+  /* Override the event engine with our test event engine (g_vtable); but before
+   * that, save the current event engine in g_old_vtable. We will have to set
+   * g_old_vtable back before calling grpc_shutdown() */
   init_engine_vtable();
+  g_old_vtable = grpc_get_event_engine_test_only();
   grpc_set_event_engine_test_only(&g_vtable);
 
   g_cq = grpc_completion_queue_create_for_next(NULL);
@@ -115,6 +121,10 @@ static void teardown() {
   }
 
   grpc_completion_queue_destroy(g_cq);
+
+  /* Restore the old event engine before calling grpc_shutdown */
+  grpc_set_event_engine_test_only(g_old_vtable);
+  grpc_shutdown();
 }
 
 /* A few notes about Multi-threaded benchmarks:
diff --git a/tools/distrib/python/OWNERS b/tools/distrib/python/OWNERS
new file mode 100644
index 0000000000..ea3909e0a3
--- /dev/null
+++ b/tools/distrib/python/OWNERS
@@ -0,0 +1,5 @@
+set noparent
+
+@nathanielmanistaatgoogle
+@kpayson64
+@mehrdada
diff --git a/tools/dockerfile/grpc_artifact_linux_x64/Dockerfile b/tools/dockerfile/grpc_artifact_linux_x64/Dockerfile
index c667655afb..0251b2b392 100644
--- a/tools/dockerfile/grpc_artifact_linux_x64/Dockerfile
+++ b/tools/dockerfile/grpc_artifact_linux_x64/Dockerfile
@@ -49,19 +49,7 @@ RUN apt-get update && apt-key update && apt-get install -y \
 # Install Node dependencies
 RUN touch .profile
 RUN curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.25.4/install.sh | bash
-RUN /bin/bash -l -c "nvm install 4 && npm install -g node-pre-gyp"
-
-##################
-# Python dependencies
-
-RUN apt-get update && apt-get install -y \
-    python-all-dev \
-    python3-all-dev \
-    python-pip
-
-RUN pip install pip --upgrade
-RUN pip install virtualenv
-RUN pip install futures==2.2.0 enum34==1.0.4 protobuf==3.2.0
+RUN /bin/bash -l -c "nvm install 8 && npm install -g node-pre-gyp"
 
 
 ##################
diff --git a/tools/dockerfile/grpc_artifact_linux_x86/Dockerfile b/tools/dockerfile/grpc_artifact_linux_x86/Dockerfile
index 79f230186f..2d179c8c45 100644
--- a/tools/dockerfile/grpc_artifact_linux_x86/Dockerfile
+++ b/tools/dockerfile/grpc_artifact_linux_x86/Dockerfile
@@ -49,19 +49,7 @@ RUN apt-get update && apt-key update && apt-get install -y \
 # Install Node dependencies
 RUN touch .profile
 RUN curl -o- https://raw.githubusercontent.com/creationix/nvm/v0.25.4/install.sh | bash
-RUN /bin/bash -l -c "nvm install 4 && npm install -g node-pre-gyp"
-
-##################
-# Python dependencies
-
-RUN apt-get update && apt-get install -y \
-    python-all-dev \
-    python3-all-dev \
-    python-pip
-
-RUN pip install pip --upgrade
-RUN pip install virtualenv
-RUN pip install futures==2.2.0 enum34==1.0.4 protobuf==3.2.0
+RUN /bin/bash -l -c "nvm install 8 && npm install -g node-pre-gyp"
 
 
 ##################
diff --git a/tools/mkowners/mkowners.py b/tools/mkowners/mkowners.py
index 18afe3a2f0..2ccedfcfb8 100755
--- a/tools/mkowners/mkowners.py
+++ b/tools/mkowners/mkowners.py
@@ -126,30 +126,71 @@ owners_data = new_owners_data
 def full_dir(rules_dir, sub_path):
   return os.path.join(rules_dir, sub_path) if rules_dir != '.' else sub_path
 
-def glob_intersect(g1, g2):
-  if not g2:
-    return all(c == '*' for c in g1)
-  if not g1:
-    return all(c == '*' for c in g2)
-  c1, *t1 = g1
-  c2, *t2 = g2
-  if c1 == '*':
-    return glob_intersect(g1, t2) or glob_intersect(t1, g2)
-  if c2 == '*':
-    return glob_intersect(t1, g2) or glob_intersect(g1, t2)
-  return c1 == c2 and glob_intersect(t1, t2)
+# glob using git
+gg_cache = {}
+def git_glob(glob):
+  global gg_cache
+  if glob in gg_cache: return gg_cache[glob]
+  r = set(subprocess
+      .check_output(['git', 'ls-files', os.path.join(git_root, glob)])
+      .decode('utf-8')
+      .strip()
+      .splitlines())
+  gg_cache[glob] = r
+  return r
+
+def expand_directives(root, directives):
+  globs = collections.OrderedDict()
+  # build a table of glob --> owners
+  for directive in directives:
+    for glob in directive.globs or ['**']:
+      if glob not in globs:
+        globs[glob] = []
+      if directive.who not in globs[glob]:
+        globs[glob].append(directive.who)
+  # expand owners for intersecting globs
+  sorted_globs = sorted(globs.keys(),
+                        key=lambda g: len(git_glob(full_dir(root, g))),
+                        reverse=True)
+  out_globs = collections.OrderedDict()
+  for glob_add in sorted_globs:
+    who_add = globs[glob_add]
+    pre_items = [i for i in out_globs.items()]
+    out_globs[glob_add] = who_add.copy()
+    for glob_have, who_have in pre_items:
+      files_add = git_glob(full_dir(root, glob_add))
+      files_have = git_glob(full_dir(root, glob_have))
+      intersect = files_have.intersection(files_add)
+      if intersect:
+        for f in sorted(files_add): # sorted to ensure merge stability
+          if f not in intersect:
+            print("X", root, glob_add, glob_have)
+            out_globs[os.path.relpath(f, start=root)] = who_add
+        for who in who_have:
+          if who not in out_globs[glob_add]:
+            out_globs[glob_add].append(who)
+  return out_globs
 
 def add_parent_to_globs(parent, globs, globs_dir):
   if not parent: return
   for owners in owners_data:
     if owners.dir == parent:
-      for directive in owners.directives:
-        for dglob in directive.globs or ['**']:
-          for gglob, glob in globs.items():
-            if glob_intersect(full_dir(globs_dir, gglob),
-                              full_dir(owners.dir, dglob)):
-              if directive.who not in glob:
-                glob.append(directive.who)
+      owners_globs = expand_directives(owners.dir, owners.directives)
+      for oglob, oglob_who in owners_globs.items():
+        for gglob, gglob_who in globs.items():
+          files_parent = git_glob(full_dir(owners.dir, oglob))
+          files_child = git_glob(full_dir(globs_dir, gglob))
+          intersect = files_parent.intersection(files_child)
+          gglob_who_orig = gglob_who.copy()
+          if intersect:
+            for f in sorted(files_child): # sorted to ensure merge stability
+              if f not in intersect:
+                print("Y", full_dir(owners.dir, oglob), full_dir(globs_dir, gglob))
+                who = gglob_who_orig.copy()
+                globs[os.path.relpath(f, start=globs_dir)] = who
+            for who in oglob_who:
+              if who not in gglob_who:
+                gglob_who.append(who)
       add_parent_to_globs(owners.parent, globs, globs_dir)
       return
   assert(False)
@@ -160,19 +201,30 @@ with open(args.out, 'w') as out:
   out.write('# Auto-generated by the tools/mkowners/mkowners.py tool\n')
   out.write('# Uses OWNERS files in different modules throughout the\n')
   out.write('# repository as the source of truth for module ownership.\n')
+  written_globs = []
   while todo:
     head, *todo = todo
     if head.parent and not head.parent in done:
       todo.append(head)
       continue
-    globs = collections.OrderedDict()
-    for directive in head.directives:
-      for glob in directive.globs or ['**']:
-        if glob not in globs:
-          globs[glob] = []
-        globs[glob].append(directive.who)
+    globs = expand_directives(head.dir, head.directives)
     add_parent_to_globs(head.parent, globs, head.dir)
     for glob, owners in globs.items():
-      out.write('/%s %s\n' % (
-          full_dir(head.dir, glob), ' '.join(owners)))
+      skip = False
+      for glob1, owners1, dir1 in reversed(written_globs):
+        files = git_glob(full_dir(head.dir, glob))
+        files1 = git_glob(full_dir(dir1, glob1))
+        intersect = files.intersection(files1)
+        if files == intersect:
+          if sorted(owners) == sorted(owners1):
+            skip = True # nothing new in this rule
+            break
+        elif intersect:
+          # continuing would cause a semantic change since some files are
+          # affected differently by this rule and CODEOWNERS is order dependent
+          break
+      if not skip:
+        out.write('/%s %s\n' % (
+            full_dir(head.dir, glob), ' '.join(owners)))
+        written_globs.append((glob, owners, head.dir))
     done.add(head.dir)