Fix TaskDispatchThread (#53961)

Summary:
Pull Request resolved: #53961

Changelog: [Internal]

Fixed a bug in TaskDispatchThread. To understand bug, let me show an example. The task is scheduled to run after several seconds. It reaches loopCv_.wait_until() and waits there. There are 2 bad scenario:
1. wait_until spuriously wakes up and async task runs even before its scheduled time
2. new task is added with runSync(). New task gets added to the queue and loopCv_ is notified. Async task will run before its scheduled time and even worse queue_.pop() will remove sync task. Therefore runSync will be blocked for forever.

To fix this bug, we need to add `continue` after wait_until().

Also I added new test to prevent this bug in future.

Reviewed By: rshest

Differential Revision: D83345047

fbshipit-source-id: 37962613a123a123c0e110426ae782effe5a81c1

Author: Nurtau Toganbay

packages/react-native/ReactCxxPlatform/react/threading/TaskDispatchThread.cpp

@@ -118,6 +118,7 @@ void TaskDispatchThread::loop() noexcept {
         if (task.dispatchTime > now) {
           // Wait until the scheduled task time, if delayed
           loopCv_.wait_until(lock, task.dispatchTime);
+          continue;
         }
       } else {
         // Shutting down, skip all the remaining tasks

packages/react-native/ReactCxxPlatform/react/threading/tests/TaskDispatchThreadTests.cpp

@@ -128,10 +128,12 @@ TEST_F(TaskDispatchThreadTest, RunAsyncFromMultipleThreads) {
   EXPECT_EQ(counter.load(), 3);
 }
 
+// Test: quit() shouldn't block if it is called inside loop thread
 TEST_F(TaskDispatchThreadTest, QuitInTaskShouldntBeBlockedForever) {
   dispatcher->runSync([&] { dispatcher->quit(); });
 }
 
+// Test: quit() should wait for already running task in the thread
 TEST_F(TaskDispatchThreadTest, QuitShouldWaitAlreadyRunningTask) {
   {
     std::unique_ptr<int> counter = std::make_unique<int>(0);
@@ -147,4 +149,14 @@ TEST_F(TaskDispatchThreadTest, QuitShouldWaitAlreadyRunningTask) {
   // forcing dispatcher to join thread
   dispatcher.reset();
 }
+
+// Test: sync tasks shouldn't be blocked for forever due to delayed task
+TEST_F(TaskDispatchThreadTest, SyncTaskShouldntBeBlockedDueToDelayedTask) {
+  std::atomic<int> counter = 0;
+  constexpr int kHugeDelay = 100000;
+  dispatcher->runAsync([&] {}, std::chrono::seconds(kHugeDelay));
+  std::this_thread::sleep_for(std::chrono::milliseconds(50));
+  dispatcher->runSync([&] { counter++; });
+  EXPECT_EQ(counter.load(), 1);
+}
 } // namespace facebook::react