Fixing race between ~AsyncInvoker and ~AsyncClosure.

webrtc/base/asyncinvoker.cc

Index: webrtc/base/asyncinvoker.cc
diff --git a/webrtc/base/asyncinvoker.cc b/webrtc/base/asyncinvoker.cc
index cabd8b506d0575ee3e3b41a479f6f7b9fcf63ee8..b4424430393b4dffacfb918a4bfe13bb383c31ac 100644
--- a/webrtc/base/asyncinvoker.cc
+++ b/webrtc/base/asyncinvoker.cc
@@ -16,7 +16,7 @@
 
 namespace rtc {
 
-AsyncInvoker::AsyncInvoker() : invocation_complete_(false, false) {}
+AsyncInvoker::AsyncInvoker() {}
 
 AsyncInvoker::~AsyncInvoker() {
   destroying_ = true;
@@ -25,12 +25,12 @@ AsyncInvoker::~AsyncInvoker() {
   // And we need to wait for any invocations that are still in progress on
   // other threads.
   while (AtomicOps::AcquireLoad(&pending_invocations_)) {
-    // If the destructor was called while AsyncInvoke was being called by
-    // another thread, WITHIN an AsyncInvoked functor, it may do another
-    // Thread::Post even after we called MessageQueueManager::Clear(this). So
-    // we need to keep calling Clear to discard these posts.
+    // Release time slice to allow other async-invoked tasks to make progress.
+    rtc::Thread::Current()->SleepMs(0);

[nisse-webrtc, 2017/05/19 07:16:59]

I think it's better with some small but non-zero value, say 10ms, so we don't
hog the cpu if the pending tasks is sleeping.

+    // One of the async-invoked tasks in progress could have posted an
+    // additional task to the current thread. So we need to keep calling Clear
+    // to discard these posts.
     MessageQueueManager::Clear(this);

[nisse-webrtc, 2017/05/19 07:16:59]

According to the comment, we only need to clear the queue for the current
thread. Then

  rtc::Thread::Current()->Clear(this);

should be enough, right? The MessageQueueManager method iterates over all
MessageQueues it knows about.

-    invocation_complete_.Wait(Event::kForever);
   }
 }
 
@@ -69,7 +69,6 @@ void AsyncInvoker::DoInvoke(const Location& posted_from,
     LOG(LS_WARNING) << "Tried to invoke while destroying the invoker.";
     return;
   }
-  AtomicOps::Increment(&pending_invocations_);
   thread->Post(posted_from, this, id,
                new ScopedMessageData<AsyncClosure>(std::move(closure)));
 }
@@ -83,7 +82,6 @@ void AsyncInvoker::DoInvokeDelayed(const Location& posted_from,
     LOG(LS_WARNING) << "Tried to invoke while destroying the invoker.";
     return;
   }
-  AtomicOps::Increment(&pending_invocations_);
   thread->PostDelayed(posted_from, delay_ms, this, id,
                       new ScopedMessageData<AsyncClosure>(std::move(closure)));
 }
@@ -111,9 +109,12 @@ void GuardedAsyncInvoker::ThreadDestroyed() {
   thread_ = nullptr;
 }
 
+AsyncClosure::AsyncClosure(AsyncInvoker* invoker) : invoker_(invoker) {
+  AtomicOps::Increment(&invoker_->pending_invocations_);
+}
+
 AsyncClosure::~AsyncClosure() {
   AtomicOps::Decrement(&invoker_->pending_invocations_);
-  invoker_->invocation_complete_.Set();
 }
 
 NotifyingAsyncClosureBase::NotifyingAsyncClosureBase(