Add TaskScheduler::JoinForTesting().

base/task_scheduler/scheduler_worker.h

 // Copyright 2016 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_TASK_SCHEDULER_SCHEDULER_WORKER_H_
 #define BASE_TASK_SCHEDULER_SCHEDULER_WORKER_H_
 
 #include <memory>
 
 #include "base/base_export.h"
@@ skipping 58 matching lines @@
     // GetWork() returned nullptr.
     //
     // It is the responsibility of the delegate to determine if detachment is
     // safe. If the delegate is responsible for thread-affine work, detachment
     // is generally not safe.
     //
     // When true is returned:
     // - The next WakeUp() could be more costly due to new thread creation.
     // - The worker will take this as a signal that it can detach, but it is not
     //   obligated to do so.
-    // This MUST return false if SchedulerWorker::JoinForTesting() is in
-    // progress.
     virtual bool CanDetach(SchedulerWorker* worker) = 0;
 
     // Called by a thread before it detaches. This method is not allowed to
     // acquire a SchedulerLock because it is called within the scope of another
     // SchedulerLock.
     virtual void OnDetach() = 0;
   };
 
   enum class InitialState { ALIVE, DETACHED };
 
@@ skipping 19 matching lines @@
   // is called, this SchedulerWorker will run Tasks from Sequences
   // returned by the GetWork() method of its delegate until it returns nullptr.
   // WakeUp() may fail if the worker is detached and it fails to allocate a new
   // worker. If this happens, there will be no call to GetWork().
   void WakeUp();
 
   SchedulerWorker::Delegate* delegate() { return delegate_.get(); }
 
   // Joins this SchedulerWorker. If a Task is already running, it will be
   // allowed to complete its execution. This can only be called once.
+  //
+  // Note: A thread that detaches before JoinForTesting() is called may still be
+  // running after JoinForTesting() returns. However, it can't run tasks after
+  // JoinForTesting() returns.
   void JoinForTesting();
 
   // Returns true if the worker is alive.
   bool ThreadAliveForTesting() const;
 
  private:
   class Thread;
 
   SchedulerWorker(ThreadPriority thread_priority,
                   std::unique_ptr<Delegate> delegate,
@@ skipping 21 matching lines @@
   // Set once JoinForTesting() has been called.
   AtomicFlag should_exit_for_testing_;
 
   DISALLOW_COPY_AND_ASSIGN(SchedulerWorker);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_SCHEDULER_WORKER_H_