Support re-entrant calls to MessageQueueManager::Clear.

webrtc/rtc_base/messagequeue.cc

 /*
  *  Copyright 2004 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.
  */
 #include <algorithm>
 
 #include "webrtc/rtc_base/atomicops.h"
 #include "webrtc/rtc_base/checks.h"
 #include "webrtc/rtc_base/logging.h"
 #include "webrtc/rtc_base/messagequeue.h"
 #include "webrtc/rtc_base/stringencode.h"
 #include "webrtc/rtc_base/thread.h"
 #include "webrtc/rtc_base/trace_event.h"
 
 namespace rtc {
 namespace {
 
 const int kMaxMsgLatency = 150;  // 150 ms
 const int kSlowDispatchLoggingThreshold = 50;  // 50 ms
 
-class SCOPED_LOCKABLE DebugNonReentrantCritScope {
- public:
-  DebugNonReentrantCritScope(const CriticalSection* cs, bool* locked)
-      EXCLUSIVE_LOCK_FUNCTION(cs)
-      : cs_(cs), locked_(locked) {
-    cs_->Enter();
-    RTC_DCHECK(!*locked_);
-    *locked_ = true;
-  }
-
-  ~DebugNonReentrantCritScope() UNLOCK_FUNCTION() {
-    *locked_ = false;
-    cs_->Leave();
-  }
-
- private:
-  const CriticalSection* const cs_;
-  bool* locked_;
-
-  RTC_DISALLOW_COPY_AND_ASSIGN(DebugNonReentrantCritScope);
-};

[Taylor Brandstetter, 2017/07/05 22:41:47]

This still seems like a useful type of helper class, to ensure we never
increment "processing_" and forget to decrement it.

[joachim, 2017/07/05 23:03:11]

Done (renamed to "MarkProcessingCritScope").

-
 class FunctorPostMessageHandler : public MessageHandler {
  public:
   void OnMessage(Message* msg) override {
     RunnableData* data = static_cast<RunnableData*>(msg->pdata);
     data->Run();
     delete data;
   }
 };
 
 }  // namespace
 
 //------------------------------------------------------------------
 // MessageQueueManager
 
 MessageQueueManager* MessageQueueManager::instance_ = nullptr;
 
 MessageQueueManager* MessageQueueManager::Instance() {
   // Note: This is not thread safe, but it is first called before threads are
   // spawned.
   if (!instance_)
     instance_ = new MessageQueueManager;
   return instance_;
 }
 
 bool MessageQueueManager::IsInitialized() {
   return instance_ != nullptr;
 }
 
-MessageQueueManager::MessageQueueManager() : locked_(false) {}
+MessageQueueManager::MessageQueueManager() : processing_(0) {}
 
 MessageQueueManager::~MessageQueueManager() {
 }
 
 void MessageQueueManager::Add(MessageQueue *message_queue) {
   return Instance()->AddInternal(message_queue);
 }
 void MessageQueueManager::AddInternal(MessageQueue *message_queue) {
-  DebugNonReentrantCritScope cs(&crit_, &locked_);
+  CritScope cs(&crit_);
+  // Prevent changes while the list of message queues is processed.
+  RTC_DCHECK_EQ(processing_, 0);
   message_queues_.push_back(message_queue);
 }
 
 void MessageQueueManager::Remove(MessageQueue *message_queue) {
   // If there isn't a message queue manager instance, then there isn't a queue
   // to remove.
   if (!instance_) return;
   return Instance()->RemoveInternal(message_queue);
 }
 void MessageQueueManager::RemoveInternal(MessageQueue *message_queue) {
   // If this is the last MessageQueue, destroy the manager as well so that
   // we don't leak this object at program shutdown. As mentioned above, this is
   // not thread-safe, but this should only happen at program termination (when
   // the ThreadManager is destroyed, and threads are no longer active).
   bool destroy = false;
   {
-    DebugNonReentrantCritScope cs(&crit_, &locked_);
+    CritScope cs(&crit_);
+    // Prevent changes while the list of message queues is processed.
+    RTC_DCHECK_EQ(processing_, 0);
     std::vector<MessageQueue *>::iterator iter;
     iter = std::find(message_queues_.begin(), message_queues_.end(),
                      message_queue);
     if (iter != message_queues_.end()) {
       message_queues_.erase(iter);
     }
     destroy = message_queues_.empty();
   }
   if (destroy) {
     instance_ = nullptr;
     delete this;
   }
 }
 
 void MessageQueueManager::Clear(MessageHandler *handler) {
   // If there isn't a message queue manager instance, then there aren't any
   // queues to remove this handler from.
   if (!instance_) return;
   return Instance()->ClearInternal(handler);
 }
 void MessageQueueManager::ClearInternal(MessageHandler *handler) {
-  DebugNonReentrantCritScope cs(&crit_, &locked_);
+  CritScope cs(&crit_);

[Taylor Brandstetter, 2017/07/05 22:41:47]

May want to comment here that this allows a deleted Message object to cause
ClearInternal to be called again in a re-entrant fashion.

[joachim, 2017/07/05 23:03:11]

Done.

+  processing_++;
   std::vector<MessageQueue *>::iterator iter;
-  for (iter = message_queues_.begin(); iter != message_queues_.end(); iter++)
-    (*iter)->Clear(handler);
+  for (MessageQueue* queue : message_queues_) {
+    queue->Clear(handler);
+  }
+  processing_--;
 }
 
 void MessageQueueManager::ProcessAllMessageQueues() {
   if (!instance_) {
     return;
   }
   return Instance()->ProcessAllMessageQueuesInternal();
 }
 
 void MessageQueueManager::ProcessAllMessageQueuesInternal() {
   // This works by posting a delayed message at the current time and waiting
   // for it to be dispatched on all queues, which will ensure that all messages
   // that came before it were also dispatched.
   volatile int queues_not_done = 0;
 
   // This class is used so that whether the posted message is processed, or the
   // message queue is simply cleared, queues_not_done gets decremented.
   class ScopedIncrement : public MessageData {
    public:
     ScopedIncrement(volatile int* value) : value_(value) {
       AtomicOps::Increment(value_);
     }
     ~ScopedIncrement() override { AtomicOps::Decrement(value_); }
 
    private:
     volatile int* value_;
   };
 
   {
-    DebugNonReentrantCritScope cs(&crit_, &locked_);
+    CritScope cs(&crit_);
+    processing_++;
     for (MessageQueue* queue : message_queues_) {
       if (!queue->IsProcessingMessages()) {
         // If the queue is not processing messages, it can
         // be ignored. If we tried to post a message to it, it would be dropped
         // or ignored.
         continue;
       }
       queue->PostDelayed(RTC_FROM_HERE, 0, nullptr, MQID_DISPOSE,
                          new ScopedIncrement(&queues_not_done));
     }
+    processing_--;
   }
   // Note: One of the message queues may have been on this thread, which is why
   // we can't synchronously wait for queues_not_done to go to 0; we need to
   // process messages as well.
   while (AtomicOps::AcquireLoad(&queues_not_done) > 0) {
     rtc::Thread::Current()->ProcessMessages(0);
   }
 }
 
 //------------------------------------------------------------------
@@ skipping 363 matching lines @@
 
 void MessageQueue::PostFunctorInternal(const Location& posted_from,
                                        RunnableData* message_data) {
   // Use static to ensure it outlives this scope. Safe since
   // FunctorPostMessageHandler keeps no state.
   static FunctorPostMessageHandler handler;
   Post(posted_from, &handler, 0, message_data);
 }
 
 }  // namespace rtc