Add rtc::Thread::PostDelayedTask

Earlier, rtc::Thread::PostTask was added as a convenient
alternative to MessageHandlers. This CL additionally adds support
for posting delayed tasks in a similar manner.

Bug: webrtc:10294
Change-Id: I0957b59ca2133a882c980bd2ad109fa03d701a16
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/161740
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30069}

rtc_base/thread.cc

@@ -63,6 +63,24 @@ class ScopedAutoReleasePool {
 #endif
 
 namespace rtc {
+namespace {
+
+class MessageHandlerWithTask final : public MessageHandler {
+ public:
+  MessageHandlerWithTask() = default;
+
+  void OnMessage(Message* msg) override {
+    static_cast<rtc_thread_internal::MessageLikeTask*>(msg->pdata)->Run();
+    delete msg->pdata;
+  }
+
+ private:
+  ~MessageHandlerWithTask() override {}
+
+  RTC_DISALLOW_COPY_AND_ASSIGN(MessageHandlerWithTask);
+};
+
+}  // namespace
 
 ThreadManager* ThreadManager::Instance() {
   static ThreadManager* const thread_manager = new ThreadManager();
@@ -612,6 +630,13 @@ bool Thread::IsRunning() {
 #endif
 }
 
+// static
+MessageHandler* Thread::GetPostTaskMessageHandler() {
+  // Allocate at first call, never deallocate.
+  static MessageHandler* handler = new MessageHandlerWithTask;
+  return handler;
+}
+
 AutoThread::AutoThread()
     : Thread(SocketServer::CreateDefault(), /*do_init=*/false) {
   if (!ThreadManager::Instance()->CurrentThread()) {

rtc_base/thread.h

@@ -64,21 +64,6 @@ class MessageWithFunctor final : public MessageLikeTask {
   RTC_DISALLOW_COPY_AND_ASSIGN(MessageWithFunctor);
 };
 
-class MessageHandlerWithTask final : public MessageHandler {
- public:
-  MessageHandlerWithTask() = default;
-
-  void OnMessage(Message* msg) override {
-    static_cast<MessageLikeTask*>(msg->pdata)->Run();
-    delete msg->pdata;
-  }
-
- private:
-  ~MessageHandlerWithTask() override {}
-
-  RTC_DISALLOW_COPY_AND_ASSIGN(MessageHandlerWithTask);
-};
-
 }  // namespace rtc_thread_internal
 
 class RTC_EXPORT ThreadManager {
@@ -267,13 +252,19 @@ class RTC_LOCKABLE RTC_EXPORT Thread : public MessageQueue,
   //                  [&x, &y] { x.TrackComputations(y.Compute()); });
   template <class FunctorT>
   void PostTask(const Location& posted_from, FunctorT&& functor) {
-    // Allocate at first call, never deallocate.
-    static auto* const handler =
-        new rtc_thread_internal::MessageHandlerWithTask;
-    Post(posted_from, handler, 0,
+    Post(posted_from, GetPostTaskMessageHandler(), /*id=*/0,
          new rtc_thread_internal::MessageWithFunctor<FunctorT>(
              std::forward<FunctorT>(functor)));
   }
+  template <class FunctorT>
+  void PostDelayedTask(const Location& posted_from,
+                       FunctorT&& functor,
+                       uint32_t milliseconds) {
+    PostDelayed(posted_from, milliseconds, GetPostTaskMessageHandler(),
+                /*id=*/0,
+                new rtc_thread_internal::MessageWithFunctor<FunctorT>(
+                    std::forward<FunctorT>(functor)));
+  }
 
   // From TaskQueueBase
   void PostTask(std::unique_ptr<webrtc::QueuedTask> task) override;
@@ -347,6 +338,7 @@ class RTC_LOCKABLE RTC_EXPORT Thread : public MessageQueue,
    public:
     void OnMessage(Message* msg) override;
   };
+
   // Sets the per-thread allow-blocking-calls flag and returns the previous
   // value. Must be called on this thread.
   bool SetAllowBlockingCalls(bool allow);
@@ -381,6 +373,10 @@ class RTC_LOCKABLE RTC_EXPORT Thread : public MessageQueue,
   void InvokeInternal(const Location& posted_from,
                       rtc::FunctionView<void()> functor);
 
+  // Returns a static-lifetime MessageHandler which runs message with
+  // MessageLikeTask payload data.
+  static MessageHandler* GetPostTaskMessageHandler();
+
   std::list<_SendMessage> sendlist_;
   std::string name_;
 

rtc_base/thread_unittest.cc

@@ -902,6 +902,48 @@ TEST(ThreadPostTaskTest, InvokesInPostedOrder) {
   fourth.Wait(Event::kForever);
 }
 
+TEST(ThreadPostDelayedTaskTest, InvokesAsynchronously) {
+  std::unique_ptr<rtc::Thread> background_thread(rtc::Thread::Create());
+  background_thread->Start();
+
+  // The first event ensures that SendSingleMessage() is not blocking this
+  // thread. The second event ensures that the message is processed.
+  Event event_set_by_test_thread;
+  Event event_set_by_background_thread;
+  background_thread->PostDelayedTask(
+      RTC_FROM_HERE,
+      Bind(&WaitAndSetEvent, &event_set_by_test_thread,
+           &event_set_by_background_thread),
+      /*milliseconds=*/10);
+  event_set_by_test_thread.Set();
+  event_set_by_background_thread.Wait(Event::kForever);
+}
+
+TEST(ThreadPostDelayedTaskTest, InvokesInDelayOrder) {
+  std::unique_ptr<rtc::Thread> background_thread(rtc::Thread::Create());
+  background_thread->Start();
+
+  Event first;
+  Event second;
+  Event third;
+  Event fourth;
+
+  background_thread->PostDelayedTask(RTC_FROM_HERE,
+                                     Bind(&WaitAndSetEvent, &third, &fourth),
+                                     /*milliseconds=*/11);
+  background_thread->PostDelayedTask(RTC_FROM_HERE,
+                                     Bind(&WaitAndSetEvent, &first, &second),
+                                     /*milliseconds=*/9);
+  background_thread->PostDelayedTask(RTC_FROM_HERE,
+                                     Bind(&WaitAndSetEvent, &second, &third),
+                                     /*milliseconds=*/10);
+
+  // All tasks have been posted before the first one is unblocked.
+  first.Set();
+  // Only if the chain is invoked in posted order will the last event be set.
+  fourth.Wait(Event::kForever);
+}
+
 class ThreadFactory : public webrtc::TaskQueueFactory {
  public:
   std::unique_ptr<webrtc::TaskQueueBase, webrtc::TaskQueueDeleter>