Fix potential deadlock in TaskQueue's libevent PostTaskAndReply implementation

webrtc/base/task_queue_unittest.cc

 /*
  *  Copyright 2016 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 19 matching lines @@
 }  // namespace
 
 TEST(TaskQueueTest, Construct) {
   static const char kQueueName[] = "Construct";
   TaskQueue queue(kQueueName);
   EXPECT_FALSE(queue.IsCurrent());
 }
 
 TEST(TaskQueueTest, PostAndCheckCurrent) {
   static const char kQueueName[] = "PostAndCheckCurrent";
+  Event event(false, false);
   TaskQueue queue(kQueueName);
 
   // We're not running a task, so there shouldn't be a current queue.
   EXPECT_FALSE(queue.IsCurrent());
   EXPECT_FALSE(TaskQueue::Current());
 
-  Event event(false, false);
   queue.PostTask(Bind(&CheckCurrent, kQueueName, &event, &queue));
   EXPECT_TRUE(event.Wait(1000));
 }
 
 TEST(TaskQueueTest, PostCustomTask) {
   static const char kQueueName[] = "PostCustomImplementation";
+  Event event(false, false);
   TaskQueue queue(kQueueName);
 
-  Event event(false, false);
-
   class CustomTask : public QueuedTask {
    public:
     explicit CustomTask(Event* event) : event_(event) {}
 
    private:
     bool Run() override {
       event_->Set();
       return false;  // Never allows the task to be deleted by the queue.
     }
 
     Event* const event_;
   } my_task(&event);
 
   // Please don't do this in production code! :)
   queue.PostTask(std::unique_ptr<QueuedTask>(&my_task));
   EXPECT_TRUE(event.Wait(1000));
 }
 
 TEST(TaskQueueTest, PostLambda) {
   static const char kQueueName[] = "PostLambda";
+  Event event(false, false);
   TaskQueue queue(kQueueName);
 
-  Event event(false, false);
   queue.PostTask([&event]() { event.Set(); });
   EXPECT_TRUE(event.Wait(1000));
 }
 
 TEST(TaskQueueTest, PostFromQueue) {
   static const char kQueueName[] = "PostFromQueue";
+  Event event(false, false);
   TaskQueue queue(kQueueName);
 
-  Event event(false, false);
   queue.PostTask(
       [&event, &queue]() { queue.PostTask([&event]() { event.Set(); }); });
   EXPECT_TRUE(event.Wait(1000));
 }
 
 TEST(TaskQueueTest, PostDelayed) {
   static const char kQueueName[] = "PostDelayed";
+  Event event(false, false);
   TaskQueue queue(kQueueName);
 
-  Event event(false, false);
   uint32_t start = Time();
   queue.PostDelayedTask(Bind(&CheckCurrent, kQueueName, &event, &queue), 100);
   EXPECT_TRUE(event.Wait(1000));
   uint32_t end = Time();
   // These tests are a little relaxed due to how "powerful" our test bots can
   // be.  Most recently we've seen windows bots fire the callback after 94-99ms,
   // which is why we have a little bit of leeway backwards as well.
   EXPECT_GE(end - start, 90u);
   EXPECT_NEAR(end - start, 190u, 100u);  // Accept 90-290.
 }
@@ skipping 19 matching lines @@
   {
     TaskQueue queue(kQueueName);
     queue.PostDelayedTask(Bind(&CheckCurrent, kQueueName, &event, &queue), 100);
   }
   EXPECT_FALSE(event.Wait(200));  // Task should not run.
 }
 
 TEST(TaskQueueTest, PostAndReply) {
   static const char kPostQueue[] = "PostQueue";
   static const char kReplyQueue[] = "ReplyQueue";
+  Event event(false, false);
   TaskQueue post_queue(kPostQueue);
   TaskQueue reply_queue(kReplyQueue);
 
-  Event event(false, false);
   post_queue.PostTaskAndReply(
       Bind(&CheckCurrent, kPostQueue, nullptr, &post_queue),
       Bind(&CheckCurrent, kReplyQueue, &event, &reply_queue), &reply_queue);
   EXPECT_TRUE(event.Wait(1000));
 }
 
 TEST(TaskQueueTest, PostAndReuse) {
   static const char kPostQueue[] = "PostQueue";
   static const char kReplyQueue[] = "ReplyQueue";
+  Event event(false, false);
   TaskQueue post_queue(kPostQueue);
   TaskQueue reply_queue(kReplyQueue);
 
   int call_count = 0;
 
   class ReusedTask : public QueuedTask {
    public:
     ReusedTask(int* counter, TaskQueue* reply_queue, Event* event)
         : counter_(counter), reply_queue_(reply_queue), event_(event) {
       EXPECT_EQ(0, *counter_);
@@ skipping 16 matching lines @@
         event_->Set();
         return true;  // Indicate that the object should be deleted.
       }
     }
 
     int* const counter_;
     TaskQueue* const reply_queue_;
     Event* const event_;
   };
 
-  Event event(false, false);
   std::unique_ptr<QueuedTask> task(
       new ReusedTask(&call_count, &reply_queue, &event));
 
   post_queue.PostTask(std::move(task));
   EXPECT_TRUE(event.Wait(1000));
 }
 
 TEST(TaskQueueTest, PostAndReplyLambda) {
   static const char kPostQueue[] = "PostQueue";
   static const char kReplyQueue[] = "ReplyQueue";
+  Event event(false, false);
   TaskQueue post_queue(kPostQueue);
   TaskQueue reply_queue(kReplyQueue);
 
-  Event event(false, false);
   bool my_flag = false;
   post_queue.PostTaskAndReply([&my_flag]() { my_flag = true; },
                               [&event]() { event.Set(); }, &reply_queue);
   EXPECT_TRUE(event.Wait(1000));
   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) {
+  Event event(false, false);
+  TaskQueue post_queue("PostQueue");
+  TaskQueue reply_queue("ReplyQueue");
+
+  post_queue.PostTaskAndReply([&event]() { event.Set(); }, []() {},
+                              &reply_queue);
+  EXPECT_TRUE(event.Wait(1000));
+}
+
 void TestPostTaskAndReply(TaskQueue* work_queue,
                           const char* work_queue_name,
                           Event* event) {
   ASSERT_FALSE(work_queue->IsCurrent());
   work_queue->PostTaskAndReply(
       Bind(&CheckCurrent, work_queue_name, nullptr, work_queue),
       NewClosure([event]() { event->Set(); }));
 }
 
 // Does a PostTaskAndReply from within a task to post and reply to the current
 // queue.  All in all there will be 3 tasks posted and run.
 TEST(TaskQueueTest, PostAndReply2) {
   static const char kQueueName[] = "PostAndReply2";
   static const char kWorkQueueName[] = "PostAndReply2_Worker";
+  Event event(false, false);
   TaskQueue queue(kQueueName);
   TaskQueue work_queue(kWorkQueueName);
 
-  Event event(false, false);
   queue.PostTask(
       Bind(&TestPostTaskAndReply, &work_queue, kWorkQueueName, &event));
   EXPECT_TRUE(event.Wait(1000));
 }
 
 // Tests posting more messages than a queue can queue up.
 // In situations like that, tasks will get dropped.
 TEST(TaskQueueTest, PostALot) {
   // To destruct the event after the queue has gone out of scope.
   Event event(false, false);
@@ skipping 15 matching lines @@
       queue.PostTask(NewClosure([&tasks_executed]() { ++tasks_executed; },
                                 [&tasks_cleaned_up]() { ++tasks_cleaned_up; }));
     event.Set();  // Unblock the first task.
   }
 
   EXPECT_GE(tasks_cleaned_up, tasks_executed);
   EXPECT_EQ(kTaskCount, tasks_cleaned_up);
 }
 
 }  // namespace rtc