Record async "task backtraces"

base/threading/worker_pool_posix.cc

 // Copyright (c) 2012 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.
 
 #include "base/threading/worker_pool_posix.h"
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
@@ skipping 122 matching lines @@
     AutoLock locked(lock_);
     DCHECK(!terminated_) << "Thread pool is already terminated.";
     terminated_ = true;
   }
   pending_tasks_available_cv_.Broadcast();
 }
 
 void PosixDynamicThreadPool::PostTask(
     const tracked_objects::Location& from_here,
     const base::Closure& task) {
-  PendingTask pending_task(from_here, task);
+  PendingTask pending_task(from_here,
+                           MessageLoop::current()->current_pending_task_,

[danakj, 2015/04/03 17:18:35]

The use of MessageLoop::current()->current_pending_task_ worries me. I think
maybe we need to ask for this off the MessageLoop's task_runner() instead. But
I'm not totally sure..

It's easy to get lost in MessageLoop. Ryan do you have a good position to
comment on this being right/wrong?

I can dig a whole bunch more if you don't have some guidance here :)

+                           task);
   AddTask(&pending_task);
 }
 
 void PosixDynamicThreadPool::AddTask(PendingTask* pending_task) {
   AutoLock locked(lock_);
   DCHECK(!terminated_) <<
       "This thread pool is already terminated.  Do not post new tasks.";
 
   pending_tasks_.push(*pending_task);
   pending_task->task.Reset();
 
   // We have enough worker threads.
   if (static_cast<size_t>(num_idle_threads_) >= pending_tasks_.size()) {
     pending_tasks_available_cv_.Signal();
   } else {
     // The new PlatformThread will take ownership of the WorkerThread object,
     // which will delete itself on exit.
     WorkerThread* worker =
         new WorkerThread(name_prefix_, this);
     PlatformThread::CreateNonJoinable(0, worker);
   }
 }
 
 PendingTask PosixDynamicThreadPool::WaitForTask() {
   AutoLock locked(lock_);
 
   if (terminated_)
-    return PendingTask(FROM_HERE, base::Closure());
+    return PendingTask(FROM_HERE, NULL, base::Closure());
 
   if (pending_tasks_.empty()) {  // No work available, wait for work.
     num_idle_threads_++;
     if (num_idle_threads_cv_.get())
       num_idle_threads_cv_->Signal();
     pending_tasks_available_cv_.TimedWait(
         TimeDelta::FromSeconds(idle_seconds_before_exit_));
     num_idle_threads_--;
     if (num_idle_threads_cv_.get())
       num_idle_threads_cv_->Signal();
     if (pending_tasks_.empty()) {
       // We waited for work, but there's still no work.  Return NULL to signal
       // the thread to terminate.
-      return PendingTask(FROM_HERE, base::Closure());
+      return PendingTask(FROM_HERE, NULL, base::Closure());
     }
   }
 
   PendingTask pending_task = pending_tasks_.front();
   pending_tasks_.pop();
   return pending_task;
 }
 
 }  // namespace base