Fixing potential AsyncInvoker deadlock that occurs for "reentrant" invocations.

webrtc/base/asyncinvoker.cc

Index: webrtc/base/asyncinvoker.cc
diff --git a/webrtc/base/asyncinvoker.cc b/webrtc/base/asyncinvoker.cc
index bfd13172f70329598dc9393d41eb660f8877e8f7..d2583091ccdcfca9d8140b9db0f3b7c4c411ece3 100644
--- a/webrtc/base/asyncinvoker.cc
+++ b/webrtc/base/asyncinvoker.cc
@@ -19,7 +19,7 @@ namespace rtc {
 AsyncInvoker::AsyncInvoker() : invocation_complete_(false, false) {}
 
 AsyncInvoker::~AsyncInvoker() {
-  destroying_ = true;
+  AtomicOps::Increment(&destroying_);
   // Messages for this need to be cleared *before* our destructor is complete.
   MessageQueueManager::Clear(this);
   // And we need to wait for any invocations that are still in progress on
@@ -44,7 +44,8 @@ void AsyncInvoker::OnMessage(Message* msg) {
 }
 
 void AsyncInvoker::Flush(Thread* thread, uint32_t id /*= MQID_ANY*/) {
-  if (destroying_) return;
+  if (AtomicOps::AcquireLoad(&destroying_))
+    return;
 
   // Run this on |thread| to reduce the number of context switches.
   if (Thread::Current() != thread) {
@@ -65,11 +66,10 @@ void AsyncInvoker::DoInvoke(const Location& posted_from,
                             Thread* thread,
                             std::unique_ptr<AsyncClosure> closure,
                             uint32_t id) {
-  if (destroying_) {
+  if (AtomicOps::AcquireLoad(&destroying_)) {
     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)));
 }
@@ -79,11 +79,10 @@ void AsyncInvoker::DoInvokeDelayed(const Location& posted_from,
                                    std::unique_ptr<AsyncClosure> closure,
                                    uint32_t delay_ms,
                                    uint32_t id) {
-  if (destroying_) {
+  if (AtomicOps::AcquireLoad(&destroying_)) {
     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)));
 }
@@ -111,6 +110,10 @@ 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();