From bc1a1b4411aa6e6e955a95f9219a9afb009274e6 Mon Sep 17 00:00:00 2001
From: Muxi Yan <mxyan@google.com>
Date: Tue, 17 Apr 2018 14:39:25 -0700
Subject: [PATCH] Comment on the fix

---
 src/objective-c/GRPCClient/private/GRPCHost.m | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/objective-c/GRPCClient/private/GRPCHost.m b/src/objective-c/GRPCClient/private/GRPCHost.m
index 07cfe1329b0..bfb1fd352c5 100644
--- a/src/objective-c/GRPCClient/private/GRPCHost.m
+++ b/src/objective-c/GRPCClient/private/GRPCHost.m
@@ -108,6 +108,9 @@ static NSMutableDictionary *kHostCache;
                                    serverName:(NSString *)serverName
                                       timeout:(NSTimeInterval)timeout
                               completionQueue:(GRPCCompletionQueue *)queue {
+  // The __block attribute is to allow channel take refcount inside @synchronized block. Without
+  // this attribute, retain of channel object happens after objc_sync_exit in release builds, which
+  // may result in channel released before used. See grpc/#15033.
   __block GRPCChannel *channel;
   // This is racing -[GRPCHost disconnect].
   @synchronized(self) {