Avoid lock/unlock for common client channel pick.

src/core/channel/client_channel.c

@@ -196,13 +196,12 @@ static int is_empty(void *p, int len) {
   return 1;
 }
 
-static void started_call(grpc_exec_ctx *exec_ctx, void *arg,
-                         int iomgr_success) {
+static void started_call_locked(grpc_exec_ctx *exec_ctx, void *arg,
+                                int iomgr_success) {
   call_data *calld = arg;
   grpc_transport_stream_op op;
   int have_waiting;
 
-  gpr_mu_lock(&calld->mu_state);
   if (calld->state == CALL_CANCELLED && calld->subchannel_call != NULL) {
     memset(&op, 0, sizeof(op));
     op.cancel_with_status = GRPC_STATUS_CANCELLED;
@@ -230,10 +229,18 @@ static void started_call(grpc_exec_ctx *exec_ctx, void *arg,
   }
 }
 
+static void started_call(grpc_exec_ctx *exec_ctx, void *arg,
+                         int iomgr_success) {
+  call_data *calld = arg;
+  gpr_mu_lock(&calld->mu_state);
+  started_call_locked(exec_ctx, arg, iomgr_success);
+}
+
 static void picked_target(grpc_exec_ctx *exec_ctx, void *arg,
                           int iomgr_success) {
   call_data *calld = arg;
   grpc_pollset *pollset;
+  grpc_subchannel_call_create_status call_creation_status;
 
   if (calld->picked_channel == NULL) {
     /* treat this like a cancellation */
@@ -248,11 +255,15 @@ static void picked_target(grpc_exec_ctx *exec_ctx, void *arg,
       GPR_ASSERT(calld->state == CALL_WAITING_FOR_PICK);
       calld->state = CALL_WAITING_FOR_CALL;
       pollset = calld->waiting_op.bind_pollset;
-      gpr_mu_unlock(&calld->mu_state);
       grpc_closure_init(&calld->async_setup_task, started_call, calld);
-      grpc_subchannel_create_call(exec_ctx, calld->picked_channel, pollset,
-                                  &calld->subchannel_call,
-                                  &calld->async_setup_task);
+      call_creation_status = grpc_subchannel_create_call(
+          exec_ctx, calld->picked_channel, pollset, &calld->subchannel_call,
+          &calld->async_setup_task);
+      if (call_creation_status == GRPC_SUBCHANNEL_CALL_CREATE_READY) {
+        started_call_locked(exec_ctx, calld, iomgr_success);
+      } else {
+        gpr_mu_unlock(&calld->mu_state);
+      }
     }
   }
 }

src/core/client_config/subchannel.c

@@ -335,18 +335,20 @@ static void start_connect(grpc_exec_ctx *exec_ctx, grpc_subchannel *c) {
 
 static void continue_creating_call(grpc_exec_ctx *exec_ctx, void *arg,
                                    int iomgr_success) {
+  grpc_subchannel_call_create_status call_creation_status;
   waiting_for_connect *w4c = arg;
   grpc_subchannel_del_interested_party(exec_ctx, w4c->subchannel, w4c->pollset);
-  grpc_subchannel_create_call(exec_ctx, w4c->subchannel, w4c->pollset,
-                              w4c->target, w4c->notify);
+  call_creation_status = grpc_subchannel_create_call(
+      exec_ctx, w4c->subchannel, w4c->pollset, w4c->target, w4c->notify);
+  GPR_ASSERT(call_creation_status == GRPC_SUBCHANNEL_CALL_CREATE_READY);
+  w4c->notify->cb(exec_ctx, w4c->notify->cb_arg, iomgr_success);
   GRPC_SUBCHANNEL_UNREF(exec_ctx, w4c->subchannel, "waiting_for_connect");
   gpr_free(w4c);
 }
 
-void grpc_subchannel_create_call(grpc_exec_ctx *exec_ctx, grpc_subchannel *c,
-                                 grpc_pollset *pollset,
-                                 grpc_subchannel_call **target,
-                                 grpc_closure *notify) {
+grpc_subchannel_call_create_status grpc_subchannel_create_call(
+    grpc_exec_ctx *exec_ctx, grpc_subchannel *c, grpc_pollset *pollset,
+    grpc_subchannel_call **target, grpc_closure *notify) {
   connection *con;
   gpr_mu_lock(&c->mu);
   if (c->active != NULL) {
@@ -355,7 +357,7 @@ void grpc_subchannel_create_call(grpc_exec_ctx *exec_ctx, grpc_subchannel *c,
     gpr_mu_unlock(&c->mu);
 
     *target = create_call(exec_ctx, con);
-    notify->cb(exec_ctx, notify->cb_arg, 1);
+    return GRPC_SUBCHANNEL_CALL_CREATE_READY;
   } else {
     waiting_for_connect *w4c = gpr_malloc(sizeof(*w4c));
     w4c->next = c->waiting;
@@ -380,6 +382,7 @@ void grpc_subchannel_create_call(grpc_exec_ctx *exec_ctx, grpc_subchannel *c,
     } else {
       gpr_mu_unlock(&c->mu);
     }
+    return GRPC_SUBCHANNEL_CALL_CREATE_PENDING;
   }
 }
 

src/core/client_config/subchannel.h

@@ -75,12 +75,22 @@ void grpc_subchannel_call_unref(grpc_exec_ctx *exec_ctx,
                                 grpc_subchannel_call *call
                                     GRPC_SUBCHANNEL_REF_EXTRA_ARGS);
 
-/** construct a call (possibly asynchronously) */
-void grpc_subchannel_create_call(grpc_exec_ctx *exec_ctx,
-                                 grpc_subchannel *subchannel,
-                                 grpc_pollset *pollset,
-                                 grpc_subchannel_call **target,
-                                 grpc_closure *notify);
+typedef enum {
+  GRPC_SUBCHANNEL_CALL_CREATE_READY,
+  GRPC_SUBCHANNEL_CALL_CREATE_PENDING
+} grpc_subchannel_call_create_status;
+
+/** construct a subchannel call (possibly asynchronously).
+ *
+ * If the returned status is \a GRPC_SUBCHANNEL_CALL_CREATE_READY, the call will
+ * return immediately and \a target will point to a connected \a subchannel_call
+ * instance. Note that \a notify will \em not be invoked in this case.
+ * Otherwise, if the returned status is GRPC_SUBCHANNEL_CALL_CREATE_PENDING, the
+ * subchannel call will be created asynchronously, invoking the \a notify
+ * callback upon completion. */
+grpc_subchannel_call_create_status grpc_subchannel_create_call(
+    grpc_exec_ctx *exec_ctx, grpc_subchannel *subchannel, grpc_pollset *pollset,
+    grpc_subchannel_call **target, grpc_closure *notify);
 
 /** process a transport level op */
 void grpc_subchannel_process_transport_op(grpc_exec_ctx *exec_ctx,