TaskScheduler: Record TaskScheduler.NumTasksBeforeDetach.* from OnDetach().

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 20 matching lines @@
 // also periodically checks with its TaskTracker whether shutdown has completed
 // and exits when it has.
 //
 // The worker is free to release and reallocate the platform thread with
 // guidance from the delegate.
 //
 // This class is thread-safe.
 class BASE_EXPORT SchedulerWorker {
  public:
   // Delegate interface for SchedulerWorker. The methods are always called from
-  // a thread managed by the SchedulerWorker instance.
+  // a thread managed by the SchedulerWorker instance. The methods are never

[gab, 2016/10/19 18:12:23]

s/a thread/the thread/ (and remove last sentence -- IMO as-is it confusingly can
be read as the SchedulerWorker instance having many threads but managing
synchronization)

[fdoray, 2016/10/20 13:45:02]

Done.

+  // called concurrently.
   class Delegate {
    public:
     virtual ~Delegate() = default;
 
     // Called by a thread managed by |worker| when it enters its main function.
     // If a thread is recreated after detachment, |detach_duration| is the time
     // elapsed since detachment. Otherwise, if this is the first thread created
     // for |worker|, |detach_duration| is TimeDelta::Max().
-    virtual void OnMainEntry(SchedulerWorker* worker,
-                             const TimeDelta& detach_duration) = 0;
+    virtual void OnMainEntry(SchedulerWorker* worker) = 0;
 
     // Called by a thread managed by |worker| to get a Sequence from which to
     // run a Task.
     virtual scoped_refptr<Sequence> GetWork(SchedulerWorker* worker) = 0;
 
     // Called by the SchedulerWorker after it ran a task with |task_priority|.
     // |task_latency| is the time elapsed between when the task was posted and
     // when it started to run.
     virtual void DidRunTaskWithPriority(TaskPriority task_priority,
                                         const TimeDelta& task_latency) = 0;
@@ skipping 14 matching lines @@
     // 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 };
 
   // Creates a SchedulerWorker that runs Tasks from Sequences returned by
   // |delegate|. |priority_hint| is the preferred thread priority; the actual
   // thread priority depends on shutdown state and platform capabilities.
   // |task_tracker| is used to handle shutdown behavior of Tasks. If
   // |worker_state| is DETACHED, the thread will be created upon a WakeUp().
   // Returns nullptr if creating the underlying platform thread fails during
@@ skipping 40 matching lines @@
   void CreateThread();
 
   void CreateThreadAssertSynchronized();
 
   // Synchronizes access to |thread_|.
   mutable SchedulerLock thread_lock_;
 
   // The underlying thread for this SchedulerWorker.
   std::unique_ptr<Thread> thread_;
 
-  // Time of the last successful Detach(). Is only accessed from the thread
-  // managed by this SchedulerWorker.
-  TimeTicks last_detach_time_;
-
   const ThreadPriority priority_hint_;
   const std::unique_ptr<Delegate> delegate_;
   TaskTracker* const task_tracker_;
 
   // 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_