Record async "task backtraces"

base/message_loop/message_loop.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_MESSAGE_LOOP_MESSAGE_LOOP_H_
 #define BASE_MESSAGE_LOOP_MESSAGE_LOOP_H_
 
 #include <memory>
 #include <queue>
 #include <string>
@@ skipping 328 matching lines @@
   // A subclass can invoke this constructor to create a message_loop of a
   // specific type with a custom loop. The implementation does not call
   // BindToCurrentThread. If this constructor is invoked directly by a subclass,
   // then the subclass must subsequently bind the message loop.
   MessageLoop(Type type, MessagePumpFactoryCallback pump_factory);
 
   // Configure various members and bind this message loop to the current thread.
   void BindToCurrentThread();
 
  private:
+  friend class internal::IncomingTaskQueue;
   friend class RunLoop;
-  friend class internal::IncomingTaskQueue;
   friend class ScheduleWorkTest;
   friend class Thread;
+  friend struct PendingTask;
   FRIEND_TEST_ALL_PREFIXES(MessageLoopTest, DeleteUnboundLoop);
 
   // Creates a MessageLoop without binding to a thread.
   // If |type| is TYPE_CUSTOM non-null |pump_factory| must be also given
   // to create a message pump for this message loop.  Otherwise a default
   // message pump for the |type| is created.
   //
   // It is valid to call this to create a new message loop on one thread,
   // and then pass it to the thread where the message loop actually runs.
   // The message loop's BindToCurrentThread() method must be called on the
@@ skipping 80 matching lines @@
   // pump_factory_.Run() is called to create a message pump for this loop
   // if type_ is TYPE_CUSTOM and pump_ is null.
   MessagePumpFactoryCallback pump_factory_;
 
   RunLoop* run_loop_;
 
   ObserverList<TaskObserver> task_observers_;
 
   debug::TaskAnnotator task_annotator_;
 
+  // Used to allow creating a breadcrumb of program counters in PostTask.
+  // Be very careful when using this variable.

[danakj, 2017/02/07 23:16:46]

careful in what way, what are the risks?

[awong, 2017/02/08 01:55:50]

rewrote comment.

+  const PendingTask* current_pending_task_;
+
   scoped_refptr<internal::IncomingTaskQueue> incoming_task_queue_;
 
   // A task runner which we haven't bound to a thread yet.
   scoped_refptr<internal::MessageLoopTaskRunner> unbound_task_runner_;
 
   // The task runner associated with this message loop.
   scoped_refptr<SingleThreadTaskRunner> task_runner_;
   std::unique_ptr<ThreadTaskRunnerHandle> thread_task_runner_handle_;
 
   // Id of the thread this message loop is bound to. Initialized once when the
@@ skipping 146 matching lines @@
 
 // Do not add any member variables to MessageLoopForIO!  This is important b/c
 // MessageLoopForIO is often allocated via MessageLoop(TYPE_IO).  Any extra
 // data that you need should be stored on the MessageLoop's pump_ instance.
 static_assert(sizeof(MessageLoop) == sizeof(MessageLoopForIO),
               "MessageLoopForIO should not have extra member variables");
 
 }  // namespace base
 
 #endif  // BASE_MESSAGE_LOOP_MESSAGE_LOOP_H_