Fix potential deadlock in TaskQueue's libevent PostTaskAndReply implementation

webrtc/base/task_queue_unittest.cc

Index: webrtc/base/task_queue_unittest.cc
diff --git a/webrtc/base/task_queue_unittest.cc b/webrtc/base/task_queue_unittest.cc
index 74433b91440117250fc72cc959326db0afa2f935..a263610acafbc1e226b10df4c73aadb18a97305c 100644
--- a/webrtc/base/task_queue_unittest.cc
+++ b/webrtc/base/task_queue_unittest.cc
@@ -206,6 +206,24 @@ TEST(TaskQueueTest, PostAndReplyLambda) {
   EXPECT_TRUE(my_flag);
 }
 
+// This test covers a particular bug that we had in the libevent implementation
+// where we could hit a deadlock while trying to post a reply task to a queue
+// that was being deleted.  The test isn't guaranteed to hit that case but it's
+// written in a way that makes it likely and by running with --gtest_repeat=1000
+// the bug would occur. Alas, now it should be fixed.
+TEST(TaskQueueTest, PostAndReplyDeadlock) {
+  static const char kPostQueue[] = "PostQueue";
+  static const char kReplyQueue[] = "ReplyQueue";
+  std::unique_ptr<TaskQueue> post_queue(new TaskQueue(kPostQueue));
+  std::unique_ptr<TaskQueue> reply_queue(new TaskQueue(kReplyQueue));
+
+  Event event(false, false);
+  post_queue->PostTaskAndReply([&event]() { event.Set(); }, []() {},
+                               reply_queue.get());
+  EXPECT_TRUE(event.Wait(1000));
+  reply_queue.reset();
+}
+
 void TestPostTaskAndReply(TaskQueue* work_queue,
                           const char* work_queue_name,
                           Event* event) {