From 0f3d47199b95098b04ee774eb2730c2812bf4dd0 Mon Sep 17 00:00:00 2001
From: Norman Maurer <norman_maurer@apple.com>
Date: Thu, 4 Feb 2016 13:41:02 +0100
Subject: [PATCH] [#4834] Fix race in AddressResolverGroup

Motivation:

We miss to use synchronized when remove the executor from the map.

Modifications:

Add synchronized(...) keyword

Result:

No more race.
---
 .../src/main/java/io/netty/resolver/AddressResolverGroup.java | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/resolver/src/main/java/io/netty/resolver/AddressResolverGroup.java b/resolver/src/main/java/io/netty/resolver/AddressResolverGroup.java
index 89b00dfa04..509475eb3e 100644
--- a/resolver/src/main/java/io/netty/resolver/AddressResolverGroup.java
+++ b/resolver/src/main/java/io/netty/resolver/AddressResolverGroup.java
@@ -73,7 +73,9 @@ public abstract class AddressResolverGroup<T extends SocketAddress> implements C
                 executor.terminationFuture().addListener(new FutureListener<Object>() {
                     @Override
                     public void operationComplete(Future<Object> future) throws Exception {
-                        resolvers.remove(executor);
+                        synchronized (resolvers) {
+                            resolvers.remove(executor);
+                        }
                         newResolver.close();
                     }
                 });