From 87d0ff663eb32e5eff6aba87bdfed62613cb01d5 Mon Sep 17 00:00:00 2001
From: ZHANG Dapeng <zdapeng@google.com>
Date: Thu, 10 Sep 2020 15:11:19 -0700
Subject: [PATCH] core: fix drainPendingCalls might be called twice

Fixing the bug: if two consecutive name resolution updates are queued together in SynchronizationContext, drainPendingCalls() might be called twice and be broken.
---
 core/src/main/java/io/grpc/internal/ManagedChannelImpl.java | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/core/src/main/java/io/grpc/internal/ManagedChannelImpl.java b/core/src/main/java/io/grpc/internal/ManagedChannelImpl.java
index b3a69bbce9b..10aa197efb6 100644
--- a/core/src/main/java/io/grpc/internal/ManagedChannelImpl.java
+++ b/core/src/main/java/io/grpc/internal/ManagedChannelImpl.java
@@ -1568,6 +1568,7 @@ public void run() {
           Status serviceConfigError = configOrError != null ? configOrError.getError() : null;
 
           ManagedChannelServiceConfig effectiveServiceConfig;
+          InternalConfigSelector prevConfigSelector = configSelector.get();
           if (!lookUpServiceConfig) {
             if (validServiceConfig != null) {
               channelLogger.log(
@@ -1639,7 +1640,9 @@ public void run() {
                   re);
             }
           }
-          realChannel.drainPendingCalls();
+          if (prevConfigSelector == INITIAL_PENDING_SELECTOR) {
+            realChannel.drainPendingCalls();
+          }
 
           Attributes effectiveAttrs = resolutionResult.getAttributes();
           // Call LB only if it's not shutdown.  If LB is shutdown, lbHelper won't match.