Enforce singleton not allowed behavior for CONTINUE_ON_SHUTDOWN tasks

base/threading/sequenced_worker_pool.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/sequenced_worker_pool.h"
 
 #include <stdint.h>
 
 #include <list>
 #include <map>
@@ skipping 228 matching lines @@
   // Gets the worker for the current thread out of thread-local storage.
   static Worker* GetForCurrentThread();
 
   // Indicates that a task is about to be run. The parameters provide
   // additional metainformation about the task being run.
   void set_running_task_info(SequenceToken token,
                              WorkerShutdown shutdown_behavior) {
     is_processing_task_ = true;
     task_sequence_token_ = token;
     task_shutdown_behavior_ = shutdown_behavior;
+
+    // It is dangerous for tasks with CONTINUE_ON_SHUTDOWN to access a class
+    // that implements base::Singleton. This will trigger a DCHECK to warn of

[robliao, 2016/04/25 23:03:30]

Put why this is the case in the comment as well. (e.g. the singleton is
generally destroyed at exit).

[manzagop (departed), 2016/04/26 13:13:44]

Also mention leaky versions are fine to access from nonjoinable threads?

[Patrick Monette, 2016/04/26 19:05:27]

Done.

[Patrick Monette, 2016/04/26 19:05:27]

Done.

+    // such cases. See the comment about CONTINUE_ON_SHUTDOWN for more details.
+    ThreadRestrictions::SetSingletonAllowed(task_shutdown_behavior_ !=
+                                            CONTINUE_ON_SHUTDOWN);
   }
 
   // Indicates that the task has finished running.
   void reset_running_task_info() { is_processing_task_ = false; }
 
   // Whether the worker is processing a task.
   bool is_processing_task() { return is_processing_task_; }
 
   SequenceToken task_sequence_token() const {
     DCHECK(is_processing_task_);
@@ skipping 1137 matching lines @@
 void SequencedWorkerPool::Shutdown(int max_new_blocking_tasks_after_shutdown) {
   DCHECK(constructor_task_runner_->BelongsToCurrentThread());
   inner_->Shutdown(max_new_blocking_tasks_after_shutdown);
 }
 
 bool SequencedWorkerPool::IsShutdownInProgress() {
   return inner_->IsShutdownInProgress();
 }
 
 }  // namespace base