Merge pull request #12736 from markdroth/grpclb_update_simplification

Simplify grpclb update handling

src/core/ext/filters/client_channel/lb_policy/grpclb/grpclb.cc

@@ -345,9 +345,6 @@ typedef struct glb_lb_policy {
   /** are we currently updating lb_call? */
   bool updating_lb_call;
 
-  /** are we currently updating lb_channel? */
-  bool updating_lb_channel;
-
   /** are we already watching the LB channel's connectivity? */
   bool watching_lb_channel;
 
@@ -360,9 +357,6 @@ typedef struct glb_lb_policy {
   /** called upon changes to the LB channel's connectivity. */
   grpc_closure lb_channel_on_connectivity_changed;
 
-  /** args from the latest update received while already updating, or NULL */
-  grpc_lb_policy_args *pending_update_args;
-
   /************************************************************/
   /*  client data associated with the LB server communication */
   /************************************************************/
@@ -982,10 +976,6 @@ static void glb_destroy(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
   }
   grpc_fake_resolver_response_generator_unref(glb_policy->response_generator);
   grpc_subchannel_index_unref();
-  if (glb_policy->pending_update_args != NULL) {
-    grpc_channel_args_destroy(exec_ctx, glb_policy->pending_update_args->args);
-    gpr_free(glb_policy->pending_update_args);
-  }
   gpr_free(glb_policy);
 }
 
@@ -1752,45 +1742,22 @@ static void glb_update_locked(grpc_exec_ctx *exec_ctx, grpc_lb_policy *policy,
   }
   const grpc_lb_addresses *addresses =
       (const grpc_lb_addresses *)arg->value.pointer.p;
-
+  // If a non-empty serverlist hasn't been received from the balancer,
+  // propagate the update to fallback_backend_addresses.
   if (glb_policy->serverlist == NULL) {
-    // If a non-empty serverlist hasn't been received from the balancer,
-    // propagate the update to fallback_backend_addresses.
     fallback_update_locked(exec_ctx, glb_policy, addresses);
-  } else if (glb_policy->updating_lb_channel) {
-    // If we have recieved serverlist from the balancer, we need to defer update
-    // when there is an in-progress one.
-    if (GRPC_TRACER_ON(grpc_lb_glb_trace)) {
-      gpr_log(GPR_INFO,
-              "Update already in progress for grpclb %p. Deferring update.",
-              (void *)glb_policy);
-    }
-    if (glb_policy->pending_update_args != NULL) {
-      grpc_channel_args_destroy(exec_ctx,
-                                glb_policy->pending_update_args->args);
-      gpr_free(glb_policy->pending_update_args);
-    }
-    glb_policy->pending_update_args = (grpc_lb_policy_args *)gpr_zalloc(
-        sizeof(*glb_policy->pending_update_args));
-    glb_policy->pending_update_args->client_channel_factory =
-        args->client_channel_factory;
-    glb_policy->pending_update_args->args = grpc_channel_args_copy(args->args);
-    glb_policy->pending_update_args->combiner = args->combiner;
-    return;
   }
-
-  glb_policy->updating_lb_channel = true;
   GPR_ASSERT(glb_policy->lb_channel != NULL);
+  // Propagate updates to the LB channel (pick_first) through the fake
+  // resolver.
   grpc_channel_args *lb_channel_args = build_lb_channel_args(
       exec_ctx, addresses, glb_policy->response_generator, args->args);
-  /* Propagate updates to the LB channel (pick first) through the fake resolver
-   */
   grpc_fake_resolver_response_generator_set_response(
       exec_ctx, glb_policy->response_generator, lb_channel_args);
   grpc_channel_args_destroy(exec_ctx, lb_channel_args);
-
+  // Start watching the LB channel connectivity for connection, if not
+  // already doing so.
   if (!glb_policy->watching_lb_channel) {
-    // Watch the LB channel connectivity for connection.
     glb_policy->lb_channel_connectivity = grpc_channel_check_connectivity_state(
         glb_policy->lb_channel, true /* try to connect */);
     grpc_channel_element *client_channel_elem = grpc_channel_stack_last_element(
@@ -1842,18 +1809,10 @@ static void glb_lb_channel_on_connectivity_changed_cb(grpc_exec_ctx *exec_ctx,
     /* fallthrough */
     case GRPC_CHANNEL_READY:
       if (glb_policy->lb_call != NULL) {
-        glb_policy->updating_lb_channel = false;
         glb_policy->updating_lb_call = true;
         grpc_call_cancel(glb_policy->lb_call, NULL);
-        // lb_on_server_status_received will pick up the cancel and reinit
+        // lb_on_server_status_received() will pick up the cancel and reinit
         // lb_call.
-        if (glb_policy->pending_update_args != NULL) {
-          grpc_lb_policy_args *args = glb_policy->pending_update_args;
-          glb_policy->pending_update_args = NULL;
-          glb_update_locked(exec_ctx, &glb_policy->base, args);
-          grpc_channel_args_destroy(exec_ctx, args->args);
-          gpr_free(args);
-        }
       } else if (glb_policy->started_picking && !glb_policy->shutting_down) {
         if (glb_policy->retry_timer_active) {
           grpc_timer_cancel(exec_ctx, &glb_policy->lb_call_retry_timer);