PR comments, take three

src/core/ext/client_channel/lb_policy.h

@@ -109,10 +109,16 @@ struct grpc_lb_policy_vtable {
 
 /*#define GRPC_LB_POLICY_REFCOUNT_DEBUG*/
 #ifdef GRPC_LB_POLICY_REFCOUNT_DEBUG
+
+/* Strong references: the policy will shutdown when they reach zero */
 #define GRPC_LB_POLICY_REF(p, r) \
   grpc_lb_policy_ref((p), __FILE__, __LINE__, (r))
 #define GRPC_LB_POLICY_UNREF(exec_ctx, p, r) \
   grpc_lb_policy_unref((exec_ctx), (p), __FILE__, __LINE__, (r))
+
+/* Weak references: they don't prevent the shutdown of the LB policy. When no
+ * strong references are left but there are still weak ones, shutdown is called.
+ * Once the weak reference also reaches zero, the LB policy is destroyed. */
 #define GRPC_LB_POLICY_WEAK_REF(p, r) \
   grpc_lb_policy_weak_ref((p), __FILE__, __LINE__, (r))
 #define GRPC_LB_POLICY_WEAK_UNREF(exec_ctx, p, r) \

src/core/ext/lb_policy/grpclb/grpclb.c

@@ -561,7 +561,7 @@ static void rr_handover_locked(grpc_exec_ctx *exec_ctx,
                               rr_connectivity->state, GRPC_ERROR_REF(error),
                               "rr_handover");
   /* subscribe */
-  GRPC_LB_POLICY_WEAK_REF(&glb_policy->base, "rr_connectiviby_cb");
+  GRPC_LB_POLICY_WEAK_REF(&glb_policy->base, "rr_connectivity_cb");
   grpc_lb_policy_notify_on_state_change(exec_ctx, glb_policy->rr_policy,
                                         &rr_connectivity->state,
                                         &rr_connectivity->on_change);
@@ -609,15 +609,15 @@ static void glb_rr_connectivity_changed(grpc_exec_ctx *exec_ctx, void *arg,
     /* RR not shutting down. Mimic the RR's policy state */
     grpc_connectivity_state_set(exec_ctx, &glb_policy->state_tracker,
                                 rr_conn_data->state, GRPC_ERROR_REF(error),
-                                "glb_rr_connectivity_changed");
-    /* resubscribe */
+                                "rr_connectivity_cb");
+    /* resubscribe. Reuse the "rr_connectivity_cb" weak ref. */
     grpc_lb_policy_notify_on_state_change(exec_ctx, glb_policy->rr_policy,
                                           &rr_conn_data->state,
                                           &rr_conn_data->on_change);
     gpr_mu_unlock(&glb_policy->mu);
   } else {
     GRPC_LB_POLICY_WEAK_UNREF(exec_ctx, &glb_policy->base,
-                              "rr_connectiviby_cb");
+                              "rr_connectivity_cb");
     gpr_free(rr_conn_data);
   }
 }
@@ -1010,9 +1010,6 @@ static void lb_call_destroy(glb_lb_policy *glb_policy) {
 static void query_for_backends_locked(grpc_exec_ctx *exec_ctx,
                                       glb_lb_policy *glb_policy) {
   GPR_ASSERT(glb_policy->lb_channel != NULL);
-  /* take a weak ref (won't prevent calling of \a glb_shutdown if the strong ref
-   * count goes to zero) to be unref'd in lb_on_server_status_received */
-  GRPC_LB_POLICY_WEAK_REF(&glb_policy->base, "query_for_backends");
   lb_call_init(glb_policy);
 
   if (grpc_lb_glb_trace) {
@@ -1056,6 +1053,9 @@ static void query_for_backends_locked(grpc_exec_ctx *exec_ctx,
   op->flags = 0;
   op->reserved = NULL;
   op++;
+  /* take a weak ref (won't prevent calling of \a glb_shutdown if the strong ref
+   * count goes to zero) to be unref'd in lb_on_server_status_received */
+  GRPC_LB_POLICY_WEAK_REF(&glb_policy->base, "lb_on_server_status_received");
   call_error = grpc_call_start_batch_and_execute(
       exec_ctx, glb_policy->lb_call, ops, (size_t)(op - ops),
       &glb_policy->lb_on_server_status_received);
@@ -1067,6 +1067,8 @@ static void query_for_backends_locked(grpc_exec_ctx *exec_ctx,
   op->flags = 0;
   op->reserved = NULL;
   op++;
+  /* take another weak ref to be unref'd in lb_on_response_received */
+  GRPC_LB_POLICY_WEAK_REF(&glb_policy->base, "lb_on_response_received");
   call_error = grpc_call_start_batch_and_execute(
       exec_ctx, glb_policy->lb_call, ops, (size_t)(op - ops),
       &glb_policy->lb_on_response_received);
@@ -1145,14 +1147,19 @@ static void lb_on_response_received(grpc_exec_ctx *exec_ctx, void *arg,
       op->flags = 0;
       op->reserved = NULL;
       op++;
+      /* reuse the "lb_on_response_received" weak ref taken in
+       * query_for_backends_locked() */
       const grpc_call_error call_error = grpc_call_start_batch_and_execute(
           exec_ctx, glb_policy->lb_call, ops, (size_t)(op - ops),
           &glb_policy->lb_on_response_received); /* loop */
       GPR_ASSERT(GRPC_CALL_OK == call_error);
     }
-    return;
+  } else { /* empty payload: call cancelled. */
+           /* dispose of the "lb_on_response_received" weak ref taken in
+            * query_for_backends_locked() and reused in every reception loop */
+    GRPC_LB_POLICY_WEAK_UNREF(exec_ctx, &glb_policy->base,
+                              "lb_on_response_received_empty_payload");
   }
-  /* else, empty payload: call cancelled. */
 }
 
 static void lb_call_on_retry_timer(grpc_exec_ctx *exec_ctx, void *arg,

src/core/ext/lb_policy/round_robin/round_robin.c

@@ -270,7 +270,7 @@ static void rr_destroy(grpc_exec_ctx *exec_ctx, grpc_lb_policy *pol) {
     subchannel_data *sd = p->subchannels[i];
     GRPC_SUBCHANNEL_UNREF(exec_ctx, sd->subchannel, "round_robin_destroy");
     if (sd->user_data != NULL) {
-      GPR_ASSERT(sd->user_data_vtable);
+      GPR_ASSERT(sd->user_data_vtable != NULL);
       sd->user_data_vtable->destroy(sd->user_data);
     }
     gpr_free(sd);