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// 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.
#include <memory>
#include "base/base_export.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/synchronization/waitable_event.h"
#include "base/task_scheduler/scheduler_lock.h"
#include "base/task_scheduler/sequence.h"
#include "base/threading/platform_thread.h"
#include "base/time/time.h"
namespace base {
namespace internal {
class TaskTracker;
// A thread that runs Tasks from Sequences returned by a delegate.
// A SchedulerWorkerThread starts out sleeping. It is woken up by a call to
// WakeUp(). After a wake-up, a SchedulerWorkerThread runs Tasks from Sequences
// returned by the GetWork() method of its delegate as long as it doesn't return
// nullptr. It also periodically checks with its TaskTracker whether shutdown
// has completed and exits when it has.
// This class is thread-safe.
class BASE_EXPORT SchedulerWorkerThread : public PlatformThread::Delegate {
// Delegate interface for SchedulerWorkerThread. The methods are always called
// from the thread managed by the SchedulerWorkerThread instance.
class Delegate {
virtual ~Delegate() = default;
// Called by |worker_thread| when it enters its main function.
virtual void OnMainEntry(SchedulerWorkerThread* worker_thread) = 0;
// Called by |worker_thread| to get a Sequence from which to run a Task.
virtual scoped_refptr<Sequence> GetWork(
SchedulerWorkerThread* worker_thread) = 0;
// Called when |sequence| isn't empty after the SchedulerWorkerThread pops a
// Task from it. |sequence| is the last Sequence returned by GetWork().
virtual void ReEnqueueSequence(scoped_refptr<Sequence> sequence) = 0;
// Called by |worker_thread| to determine how long to sleep before the next
// call to GetWork(). GetWork() may be called before this timeout expires
// if the thread's WakeUp() method is called.
virtual TimeDelta GetSleepTimeout() = 0;
// Creates a SchedulerWorkerThread with priority |thread_priority| that runs
// Tasks from Sequences returned by |delegate|. |task_tracker| is used to
// handle shutdown behavior of Tasks. Returns nullptr if creating the
// underlying platform thread fails.
static std::unique_ptr<SchedulerWorkerThread> Create(
ThreadPriority thread_priority,
std::unique_ptr<Delegate> delegate,
TaskTracker* task_tracker);
// Destroying a SchedulerWorkerThread in production is not allowed; it is
// always leaked. In tests, it can only be destroyed after JoinForTesting()
// has returned.
~SchedulerWorkerThread() override;
// Wakes up this SchedulerWorkerThread if it wasn't already awake. After this
// is called, this SchedulerWorkerThread will run Tasks from Sequences
// returned by the GetWork() method of its delegate until it returns nullptr.
void WakeUp();
SchedulerWorkerThread::Delegate* delegate() { return delegate_.get(); }
// Joins this SchedulerWorkerThread. If a Task is already running, it will be
// allowed to complete its execution. This can only be called once.
void JoinForTesting();
SchedulerWorkerThread(ThreadPriority thread_priority,
std::unique_ptr<Delegate> delegate,
TaskTracker* task_tracker);
// PlatformThread::Delegate:
void ThreadMain() override;
bool ShouldExitForTesting() const;
// Platform thread managed by this SchedulerWorkerThread.
PlatformThreadHandle thread_handle_;
// Event signaled to wake up this SchedulerWorkerThread.
WaitableEvent wake_up_event_;
const std::unique_ptr<Delegate> delegate_;
TaskTracker* const task_tracker_;
// Synchronizes access to |should_exit_for_testing_|.
mutable SchedulerLock should_exit_for_testing_lock_;
// True once JoinForTesting() has been called.
bool should_exit_for_testing_ = false;
} // namespace internal
} // namespace base