Merge pull request #12648 from kpayson64/attempt_2

Add back mpscq request matcher implementation

5 files changed, 130 insertions, 125 deletions

diff --git a/include/grpc++/server_builder.h b/include/grpc++/server_builder.h
index 0888bef0d9..bf842baf6f 100644
--- a/include/grpc++/server_builder.h
+++ b/include/grpc++/server_builder.h
@@ -202,7 +202,10 @@ class ServerBuilder {
 
   struct SyncServerSettings {
     SyncServerSettings()
-        : num_cqs(1), min_pollers(1), max_pollers(2), cq_timeout_msec(10000) {}
+        : num_cqs(GPR_MAX(1, gpr_cpu_num_cores())),
+          min_pollers(1),
+          max_pollers(2),
+          cq_timeout_msec(10000) {}
 
     /// Number of server completion queues to create to listen to incoming RPCs.
     int num_cqs;
diff --git a/src/core/lib/support/mpscq.cc b/src/core/lib/support/mpscq.cc
index db25f24264..b270777d5c 100644
--- a/src/core/lib/support/mpscq.cc
+++ b/src/core/lib/support/mpscq.cc
@@ -31,11 +31,12 @@ void gpr_mpscq_destroy(gpr_mpscq* q) {
   GPR_ASSERT(q->tail == &q->stub);
 }
 
-void gpr_mpscq_push(gpr_mpscq* q, gpr_mpscq_node* n) {
+bool gpr_mpscq_push(gpr_mpscq* q, gpr_mpscq_node* n) {
   gpr_atm_no_barrier_store(&n->next, (gpr_atm)NULL);
   gpr_mpscq_node* prev =
       (gpr_mpscq_node*)gpr_atm_full_xchg(&q->head, (gpr_atm)n);
   gpr_atm_rel_store(&prev->next, (gpr_atm)n);
+  return prev == &q->stub;
 }
 
 gpr_mpscq_node* gpr_mpscq_pop(gpr_mpscq* q) {
@@ -77,3 +78,37 @@ gpr_mpscq_node* gpr_mpscq_pop_and_check_end(gpr_mpscq* q, bool* empty) {
   *empty = false;
   return NULL;
 }
+
+void gpr_locked_mpscq_init(gpr_locked_mpscq* q) {
+  gpr_mpscq_init(&q->queue);
+  gpr_mu_init(&q->mu);
+}
+
+void gpr_locked_mpscq_destroy(gpr_locked_mpscq* q) {
+  gpr_mpscq_destroy(&q->queue);
+  gpr_mu_destroy(&q->mu);
+}
+
+bool gpr_locked_mpscq_push(gpr_locked_mpscq* q, gpr_mpscq_node* n) {
+  return gpr_mpscq_push(&q->queue, n);
+}
+
+gpr_mpscq_node* gpr_locked_mpscq_try_pop(gpr_locked_mpscq* q) {
+  if (gpr_mu_trylock(&q->mu)) {
+    gpr_mpscq_node* n = gpr_mpscq_pop(&q->queue);
+    gpr_mu_unlock(&q->mu);
+    return n;
+  }
+  return NULL;
+}
+
+gpr_mpscq_node* gpr_locked_mpscq_pop(gpr_locked_mpscq* q) {
+  gpr_mu_lock(&q->mu);
+  bool empty = false;
+  gpr_mpscq_node* n;
+  do {
+    n = gpr_mpscq_pop_and_check_end(&q->queue, &empty);
+  } while (n == NULL && !empty);
+  gpr_mu_unlock(&q->mu);
+  return n;
+}
diff --git a/src/core/lib/support/mpscq.h b/src/core/lib/support/mpscq.h
index 1cc9d89feb..fb22742050 100644
--- a/src/core/lib/support/mpscq.h
+++ b/src/core/lib/support/mpscq.h
@@ -20,6 +20,7 @@
 #define GRPC_CORE_LIB_SUPPORT_MPSCQ_H
 
 #include <grpc/support/atm.h>
+#include <grpc/support/sync.h>
 #include <stdbool.h>
 #include <stddef.h>
 
@@ -49,13 +50,40 @@ typedef struct gpr_mpscq {
 void gpr_mpscq_init(gpr_mpscq* q);
 void gpr_mpscq_destroy(gpr_mpscq* q);
 // Push a node
-void gpr_mpscq_push(gpr_mpscq* q, gpr_mpscq_node* n);
+// Thread safe - can be called from multiple threads concurrently
+// Returns true if this was possibly the first node (may return true
+// sporadically, will not return false sporadically)
+bool gpr_mpscq_push(gpr_mpscq* q, gpr_mpscq_node* n);
 // Pop a node (returns NULL if no node is ready - which doesn't indicate that
 // the queue is empty!!)
+// Thread compatible - can only be called from one thread at a time
 gpr_mpscq_node* gpr_mpscq_pop(gpr_mpscq* q);
 // Pop a node; sets *empty to true if the queue is empty, or false if it is not
 gpr_mpscq_node* gpr_mpscq_pop_and_check_end(gpr_mpscq* q, bool* empty);
 
+// An mpscq with a lock: it's safe to pop from multiple threads, but doing
+// only one thread will succeed concurrently
+typedef struct gpr_locked_mpscq {
+  gpr_mpscq queue;
+  gpr_mu mu;
+} gpr_locked_mpscq;
+
+void gpr_locked_mpscq_init(gpr_locked_mpscq* q);
+void gpr_locked_mpscq_destroy(gpr_locked_mpscq* q);
+// Push a node
+// Thread safe - can be called from multiple threads concurrently
+// Returns true if this was possibly the first node (may return true
+// sporadically, will not return false sporadically)
+bool gpr_locked_mpscq_push(gpr_locked_mpscq* q, gpr_mpscq_node* n);
+
+// Pop a node (returns NULL if no node is ready - which doesn't indicate that
+// the queue is empty!!)
+// Thread safe - can be called from multiple threads concurrently
+gpr_mpscq_node* gpr_locked_mpscq_try_pop(gpr_locked_mpscq* q);
+
+// Pop a node.  Returns NULL only if the queue was empty at some point after
+// calling this function
+gpr_mpscq_node* gpr_locked_mpscq_pop(gpr_locked_mpscq* q);
 #ifdef __cplusplus
 }
 #endif
diff --git a/src/core/lib/surface/completion_queue.cc b/src/core/lib/surface/completion_queue.cc
index 14054e82e7..922df923ae 100644
--- a/src/core/lib/surface/completion_queue.cc
+++ b/src/core/lib/surface/completion_queue.cc
@@ -376,8 +376,8 @@ int grpc_completion_queue_thread_local_cache_flush(grpc_completion_queue* cq,
       (grpc_completion_queue*)gpr_tls_get(&g_cached_cq) == cq) {
     *tag = storage->tag;
     grpc_exec_ctx exec_ctx = GRPC_EXEC_CTX_INIT;
-    storage->done(&exec_ctx, storage->done_arg, storage);
     *ok = (storage->next & (uintptr_t)(1)) == 1;
+    storage->done(&exec_ctx, storage->done_arg, storage);
     ret = 1;
     cq_next_data* cqd = (cq_next_data*)DATA_FROM_CQ(cq);
     if (gpr_atm_full_fetch_add(&cqd->pending_events, -1) == 1) {
diff --git a/src/core/lib/surface/server.cc b/src/core/lib/surface/server.cc
index eb7a4e2d30..da7ae17bef 100644
--- a/src/core/lib/surface/server.cc
+++ b/src/core/lib/surface/server.cc
@@ -33,7 +33,8 @@
 #include "src/core/lib/iomgr/executor.h"
 #include "src/core/lib/iomgr/iomgr.h"
 #include "src/core/lib/slice/slice_internal.h"
-#include "src/core/lib/support/stack_lockfree.h"
+#include "src/core/lib/support/mpscq.h"
+#include "src/core/lib/support/spinlock.h"
 #include "src/core/lib/support/string.h"
 #include "src/core/lib/surface/api_trace.h"
 #include "src/core/lib/surface/call.h"
@@ -63,6 +64,7 @@ grpc_tracer_flag grpc_server_channel_trace =
     GRPC_TRACER_INITIALIZER(false, "server_channel");
 
 typedef struct requested_call {
+  gpr_mpscq_node request_link; /* must be first */
   requested_call_type type;
   size_t cq_idx;
   void* tag;
@@ -128,10 +130,7 @@ typedef struct request_matcher request_matcher;
 struct call_data {
   grpc_call* call;
 
-  /** protects state */
-  gpr_mu mu_state;
-  /** the current state of a call - see call_state */
-  call_state state;
+  gpr_atm state;
 
   bool path_set;
   bool host_set;
@@ -162,7 +161,7 @@ struct request_matcher {
   grpc_server* server;
   call_data* pending_head;
   call_data* pending_tail;
-  gpr_stack_lockfree** requests_per_cq;
+  gpr_locked_mpscq* requests_per_cq;
 };
 
 struct registered_method {
@@ -207,11 +206,6 @@ struct grpc_server {
   registered_method* registered_methods;
   /** one request matcher for unregistered methods */
   request_matcher unregistered_request_matcher;
-  /** free list of available requested_calls_per_cq indices */
-  gpr_stack_lockfree** request_freelist_per_cq;
-  /** requested call backing data */
-  requested_call** requested_calls_per_cq;
-  int max_requested_calls_per_cq;
 
   gpr_atm shutdown_flag;
   uint8_t shutdown_published;
@@ -313,21 +307,20 @@ static void channel_broadcaster_shutdown(grpc_exec_ctx* exec_ctx,
  * request_matcher
  */
 
-static void request_matcher_init(request_matcher* rm, size_t entries,
-                                 grpc_server* server) {
+static void request_matcher_init(request_matcher* rm, grpc_server* server) {
   memset(rm, 0, sizeof(*rm));
   rm->server = server;
-  rm->requests_per_cq = (gpr_stack_lockfree**)gpr_malloc(
+  rm->requests_per_cq = (gpr_locked_mpscq*)gpr_malloc(
       sizeof(*rm->requests_per_cq) * server->cq_count);
   for (size_t i = 0; i < server->cq_count; i++) {
-    rm->requests_per_cq[i] = gpr_stack_lockfree_create(entries);
+    gpr_locked_mpscq_init(&rm->requests_per_cq[i]);
   }
 }
 
 static void request_matcher_destroy(request_matcher* rm) {
   for (size_t i = 0; i < rm->server->cq_count; i++) {
-    GPR_ASSERT(gpr_stack_lockfree_pop(rm->requests_per_cq[i]) == -1);
-    gpr_stack_lockfree_destroy(rm->requests_per_cq[i]);
+    GPR_ASSERT(gpr_locked_mpscq_pop(&rm->requests_per_cq[i]) == NULL);
+    gpr_locked_mpscq_destroy(&rm->requests_per_cq[i]);
   }
   gpr_free(rm->requests_per_cq);
 }
@@ -342,9 +335,7 @@ static void request_matcher_zombify_all_pending_calls(grpc_exec_ctx* exec_ctx,
   while (rm->pending_head) {
     call_data* calld = rm->pending_head;
     rm->pending_head = calld->pending_next;
-    gpr_mu_lock(&calld->mu_state);
-    calld->state = ZOMBIED;
-    gpr_mu_unlock(&calld->mu_state);
+    gpr_atm_no_barrier_store(&calld->state, ZOMBIED);
     GRPC_CLOSURE_INIT(
         &calld->kill_zombie_closure, kill_zombie,
         grpc_call_stack_element(grpc_call_get_call_stack(calld->call), 0),
@@ -357,13 +348,17 @@ static void request_matcher_kill_requests(grpc_exec_ctx* exec_ctx,
                                           grpc_server* server,
                                           request_matcher* rm,
                                           grpc_error* error) {
-  int request_id;
+  requested_call* rc;
   for (size_t i = 0; i < server->cq_count; i++) {
-    while ((request_id = gpr_stack_lockfree_pop(rm->requests_per_cq[i])) !=
-           -1) {
-      fail_call(exec_ctx, server, i,
-                &server->requested_calls_per_cq[i][request_id],
-                GRPC_ERROR_REF(error));
+    /* Here we know:
+       1. no requests are being added (since the server is shut down)
+       2. no other threads are pulling (since the shut down process is single
+          threaded)
+       So, we can ignore the queue lock and just pop, with the guarantee that a
+       NULL returned here truly means that the queue is empty */
+    while ((rc = (requested_call*)gpr_mpscq_pop(
+                &rm->requests_per_cq[i].queue)) != NULL) {
+      fail_call(exec_ctx, server, i, rc, GRPC_ERROR_REF(error));
     }
   }
   GRPC_ERROR_UNREF(error);
@@ -398,13 +393,7 @@ static void server_delete(grpc_exec_ctx* exec_ctx, grpc_server* server) {
   }
   for (i = 0; i < server->cq_count; i++) {
     GRPC_CQ_INTERNAL_UNREF(exec_ctx, server->cqs[i], "server");
-    if (server->started) {
-      gpr_stack_lockfree_destroy(server->request_freelist_per_cq[i]);
-      gpr_free(server->requested_calls_per_cq[i]);
-    }
   }
-  gpr_free(server->request_freelist_per_cq);
-  gpr_free(server->requested_calls_per_cq);
   gpr_free(server->cqs);
   gpr_free(server->pollsets);
   gpr_free(server->shutdown_tags);
@@ -462,21 +451,7 @@ static void destroy_channel(grpc_exec_ctx* exec_ctx, channel_data* chand,
 
 static void done_request_event(grpc_exec_ctx* exec_ctx, void* req,
                                grpc_cq_completion* c) {
-  requested_call* rc = (requested_call*)req;
-  grpc_server* server = rc->server;
-
-  if (rc >= server->requested_calls_per_cq[rc->cq_idx] &&
-      rc < server->requested_calls_per_cq[rc->cq_idx] +
-               server->max_requested_calls_per_cq) {
-    GPR_ASSERT(rc - server->requested_calls_per_cq[rc->cq_idx] <= INT_MAX);
-    gpr_stack_lockfree_push(
-        server->request_freelist_per_cq[rc->cq_idx],
-        (int)(rc - server->requested_calls_per_cq[rc->cq_idx]));
-  } else {
-    gpr_free(req);
-  }
-
-  server_unref(exec_ctx, server);
+  gpr_free(req);
 }
 
 static void publish_call(grpc_exec_ctx* exec_ctx, grpc_server* server,
@@ -508,10 +483,6 @@ static void publish_call(grpc_exec_ctx* exec_ctx, grpc_server* server,
       GPR_UNREACHABLE_CODE(return );
   }
 
-  grpc_call_element* elem =
-      grpc_call_stack_element(grpc_call_get_call_stack(call), 0);
-  channel_data* chand = (channel_data*)elem->channel_data;
-  server_ref(chand->server);
   grpc_cq_end_op(exec_ctx, calld->cq_new, rc->tag, GRPC_ERROR_NONE,
                  done_request_event, rc, &rc->completion);
 }
@@ -525,9 +496,7 @@ static void publish_new_rpc(grpc_exec_ctx* exec_ctx, void* arg,
   grpc_server* server = rm->server;
 
   if (error != GRPC_ERROR_NONE || gpr_atm_acq_load(&server->shutdown_flag)) {
-    gpr_mu_lock(&calld->mu_state);
-    calld->state = ZOMBIED;
-    gpr_mu_unlock(&calld->mu_state);
+    gpr_atm_no_barrier_store(&calld->state, ZOMBIED);
     GRPC_CLOSURE_INIT(
         &calld->kill_zombie_closure, kill_zombie,
         grpc_call_stack_element(grpc_call_get_call_stack(calld->call), 0),
@@ -539,16 +508,14 @@ static void publish_new_rpc(grpc_exec_ctx* exec_ctx, void* arg,
 
   for (size_t i = 0; i < server->cq_count; i++) {
     size_t cq_idx = (chand->cq_idx + i) % server->cq_count;
-    int request_id = gpr_stack_lockfree_pop(rm->requests_per_cq[cq_idx]);
-    if (request_id == -1) {
+    requested_call* rc =
+        (requested_call*)gpr_locked_mpscq_try_pop(&rm->requests_per_cq[cq_idx]);
+    if (rc == NULL) {
       continue;
     } else {
       GRPC_STATS_INC_SERVER_CQS_CHECKED(exec_ctx, i);
-      gpr_mu_lock(&calld->mu_state);
-      calld->state = ACTIVATED;
-      gpr_mu_unlock(&calld->mu_state);
-      publish_call(exec_ctx, server, calld, cq_idx,
-                   &server->requested_calls_per_cq[cq_idx][request_id]);
+      gpr_atm_no_barrier_store(&calld->state, ACTIVATED);
+      publish_call(exec_ctx, server, calld, cq_idx, rc);
       return; /* early out */
     }
   }
@@ -556,9 +523,27 @@ static void publish_new_rpc(grpc_exec_ctx* exec_ctx, void* arg,
   /* no cq to take the request found: queue it on the slow list */
   GRPC_STATS_INC_SERVER_SLOWPATH_REQUESTS_QUEUED(exec_ctx);
   gpr_mu_lock(&server->mu_call);
-  gpr_mu_lock(&calld->mu_state);
-  calld->state = PENDING;
-  gpr_mu_unlock(&calld->mu_state);
+
+  // We need to ensure that all the queues are empty.  We do this under
+  // the server mu_call lock to ensure that if something is added to
+  // an empty request queue, it will block until the call is actually
+  // added to the pending list.
+  for (size_t i = 0; i < server->cq_count; i++) {
+    size_t cq_idx = (chand->cq_idx + i) % server->cq_count;
+    requested_call* rc =
+        (requested_call*)gpr_locked_mpscq_pop(&rm->requests_per_cq[cq_idx]);
+    if (rc == NULL) {
+      continue;
+    } else {
+      gpr_mu_unlock(&server->mu_call);
+      GRPC_STATS_INC_SERVER_CQS_CHECKED(exec_ctx, i + server->cq_count);
+      gpr_atm_no_barrier_store(&calld->state, ACTIVATED);
+      publish_call(exec_ctx, server, calld, cq_idx, rc);
+      return; /* early out */
+    }
+  }
+
+  gpr_atm_no_barrier_store(&calld->state, PENDING);
   if (rm->pending_head == NULL) {
     rm->pending_tail = rm->pending_head = calld;
   } else {
@@ -576,9 +561,7 @@ static void finish_start_new_rpc(
   call_data* calld = (call_data*)elem->call_data;
 
   if (gpr_atm_acq_load(&server->shutdown_flag)) {
-    gpr_mu_lock(&calld->mu_state);
-    calld->state = ZOMBIED;
-    gpr_mu_unlock(&calld->mu_state);
+    gpr_atm_no_barrier_store(&calld->state, ZOMBIED);
     GRPC_CLOSURE_INIT(&calld->kill_zombie_closure, kill_zombie, elem,
                       grpc_schedule_on_exec_ctx);
     GRPC_CLOSURE_SCHED(exec_ctx, &calld->kill_zombie_closure, GRPC_ERROR_NONE);
@@ -807,21 +790,14 @@ static void got_initial_metadata(grpc_exec_ctx* exec_ctx, void* ptr,
   if (error == GRPC_ERROR_NONE) {
     start_new_rpc(exec_ctx, elem);
   } else {
-    gpr_mu_lock(&calld->mu_state);
-    if (calld->state == NOT_STARTED) {
-      calld->state = ZOMBIED;
-      gpr_mu_unlock(&calld->mu_state);
+    if (gpr_atm_full_cas(&calld->state, NOT_STARTED, ZOMBIED)) {
       GRPC_CLOSURE_INIT(&calld->kill_zombie_closure, kill_zombie, elem,
                         grpc_schedule_on_exec_ctx);
       GRPC_CLOSURE_SCHED(exec_ctx, &calld->kill_zombie_closure,
                          GRPC_ERROR_NONE);
-    } else if (calld->state == PENDING) {
-      calld->state = ZOMBIED;
-      gpr_mu_unlock(&calld->mu_state);
+    } else if (gpr_atm_full_cas(&calld->state, PENDING, ZOMBIED)) {
       /* zombied call will be destroyed when it's removed from the pending
          queue... later */
-    } else {
-      gpr_mu_unlock(&calld->mu_state);
     }
   }
 }
@@ -885,7 +861,6 @@ static grpc_error* init_call_elem(grpc_exec_ctx* exec_ctx,
   memset(calld, 0, sizeof(call_data));
   calld->deadline = GRPC_MILLIS_INF_FUTURE;
   calld->call = grpc_call_from_top_element(elem);
-  gpr_mu_init(&calld->mu_state);
 
   GRPC_CLOSURE_INIT(&calld->server_on_recv_initial_metadata,
                     server_on_recv_initial_metadata, elem,
@@ -912,8 +887,6 @@ static void destroy_call_elem(grpc_exec_ctx* exec_ctx, grpc_call_element* elem,
   grpc_metadata_array_destroy(&calld->initial_metadata);
   grpc_byte_buffer_destroy(calld->payload);
 
-  gpr_mu_destroy(&calld->mu_state);
-
   server_unref(exec_ctx, chand->server);
 }
 
@@ -1020,8 +993,6 @@ grpc_server* grpc_server_create(const grpc_channel_args* args, void* reserved) {
   server->root_channel_data.next = server->root_channel_data.prev =
       &server->root_channel_data;
 
-  /* TODO(ctiller): expose a channel_arg for this */
-  server->max_requested_calls_per_cq = 32768;
   server->channel_args = grpc_channel_args_copy(args);
 
   return server;
@@ -1095,29 +1066,15 @@ void grpc_server_start(grpc_server* server) {
   server->pollset_count = 0;
   server->pollsets =
       (grpc_pollset**)gpr_malloc(sizeof(grpc_pollset*) * server->cq_count);
-  server->request_freelist_per_cq = (gpr_stack_lockfree**)gpr_malloc(
-      sizeof(*server->request_freelist_per_cq) * server->cq_count);
-  server->requested_calls_per_cq = (requested_call**)gpr_malloc(
-      sizeof(*server->requested_calls_per_cq) * server->cq_count);
   for (i = 0; i < server->cq_count; i++) {
     if (grpc_cq_can_listen(server->cqs[i])) {
       server->pollsets[server->pollset_count++] =
           grpc_cq_pollset(server->cqs[i]);
     }
-    server->request_freelist_per_cq[i] =
-        gpr_stack_lockfree_create((size_t)server->max_requested_calls_per_cq);
-    for (int j = 0; j < server->max_requested_calls_per_cq; j++) {
-      gpr_stack_lockfree_push(server->request_freelist_per_cq[i], j);
-    }
-    server->requested_calls_per_cq[i] =
-        (requested_call*)gpr_malloc((size_t)server->max_requested_calls_per_cq *
-                                    sizeof(*server->requested_calls_per_cq[i]));
   }
-  request_matcher_init(&server->unregistered_request_matcher,
-                       (size_t)server->max_requested_calls_per_cq, server);
+  request_matcher_init(&server->unregistered_request_matcher, server);
   for (registered_method* rm = server->registered_methods; rm; rm = rm->next) {
-    request_matcher_init(&rm->matcher,
-                         (size_t)server->max_requested_calls_per_cq, server);
+    request_matcher_init(&rm->matcher, server);
   }
 
   server_ref(server);
@@ -1373,21 +1330,11 @@ static grpc_call_error queue_call_request(grpc_exec_ctx* exec_ctx,
                                           requested_call* rc) {
   call_data* calld = NULL;
   request_matcher* rm = NULL;
-  int request_id;
   if (gpr_atm_acq_load(&server->shutdown_flag)) {
     fail_call(exec_ctx, server, cq_idx, rc,
               GRPC_ERROR_CREATE_FROM_STATIC_STRING("Server Shutdown"));
     return GRPC_CALL_OK;
   }
-  request_id = gpr_stack_lockfree_pop(server->request_freelist_per_cq[cq_idx]);
-  if (request_id == -1) {
-    /* out of request ids: just fail this one */
-    fail_call(exec_ctx, server, cq_idx, rc,
-              grpc_error_set_int(
-                  GRPC_ERROR_CREATE_FROM_STATIC_STRING("Out of request ids"),
-                  GRPC_ERROR_INT_LIMIT, server->max_requested_calls_per_cq));
-    return GRPC_CALL_OK;
-  }
   switch (rc->type) {
     case BATCH_CALL:
       rm = &server->unregistered_request_matcher;
@@ -1396,20 +1343,17 @@ static grpc_call_error queue_call_request(grpc_exec_ctx* exec_ctx,
       rm = &rc->data.registered.method->matcher;
       break;
   }
-  server->requested_calls_per_cq[cq_idx][request_id] = *rc;
-  gpr_free(rc);
-  if (gpr_stack_lockfree_push(rm->requests_per_cq[cq_idx], request_id)) {
+  if (gpr_locked_mpscq_push(&rm->requests_per_cq[cq_idx], &rc->request_link)) {
     /* this was the first queued request: we need to lock and start
        matching calls */
     gpr_mu_lock(&server->mu_call);
     while ((calld = rm->pending_head) != NULL) {
-      request_id = gpr_stack_lockfree_pop(rm->requests_per_cq[cq_idx]);
-      if (request_id == -1) break;
+      rc = (requested_call*)gpr_locked_mpscq_pop(&rm->requests_per_cq[cq_idx]);
+      if (rc == NULL) break;
       rm->pending_head = calld->pending_next;
       gpr_mu_unlock(&server->mu_call);
-      gpr_mu_lock(&calld->mu_state);
-      if (calld->state == ZOMBIED) {
-        gpr_mu_unlock(&calld->mu_state);
+      if (!gpr_atm_full_cas(&calld->state, PENDING, ACTIVATED)) {
+        // Zombied Call
         GRPC_CLOSURE_INIT(
             &calld->kill_zombie_closure, kill_zombie,
             grpc_call_stack_element(grpc_call_get_call_stack(calld->call), 0),
@@ -1417,11 +1361,7 @@ static grpc_call_error queue_call_request(grpc_exec_ctx* exec_ctx,
         GRPC_CLOSURE_SCHED(exec_ctx, &calld->kill_zombie_closure,
                            GRPC_ERROR_NONE);
       } else {
-        GPR_ASSERT(calld->state == PENDING);
-        calld->state = ACTIVATED;
-        gpr_mu_unlock(&calld->mu_state);
-        publish_call(exec_ctx, server, calld, cq_idx,
-                     &server->requested_calls_per_cq[cq_idx][request_id]);
+        publish_call(exec_ctx, server, calld, cq_idx, rc);
       }
       gpr_mu_lock(&server->mu_call);
     }
@@ -1540,7 +1480,6 @@ static void fail_call(grpc_exec_ctx* exec_ctx, grpc_server* server,
   rc->initial_metadata->count = 0;
   GPR_ASSERT(error != GRPC_ERROR_NONE);
 
-  server_ref(server);
   grpc_cq_end_op(exec_ctx, server->cqs[cq_idx], rc->tag, error,
                  done_request_event, rc, &rc->completion);
 }