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* Copyright 2019 The WebRTC Project Authors. All rights reserved.
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
#include <type_traits>
#include <utility>
#include "absl/memory/memory.h"
#include "api/task_queue/queued_task.h"
#include "api/task_queue/task_queue_base.h"
#include "api/units/time_delta.h"
#include "api/units/timestamp.h"
#include "rtc_base/synchronization/sequence_checker.h"
#include "rtc_base/thread_checker.h"
namespace webrtc {
class RepeatingTaskHandle;
namespace webrtc_repeating_task_impl {
class RepeatingTaskBase : public QueuedTask {
RepeatingTaskBase(TaskQueueBase* task_queue, TimeDelta first_delay);
~RepeatingTaskBase() override;
virtual TimeDelta RunClosure() = 0;
friend class ::webrtc::RepeatingTaskHandle;
bool Run() final;
void Stop() RTC_RUN_ON(task_queue_);
TaskQueueBase* const task_queue_;
// This is always finite, except for the special case where it's PlusInfinity
// to signal that the task should stop.
Timestamp next_run_time_ RTC_GUARDED_BY(task_queue_);
// The template closure pattern is based on rtc::ClosureTask.
template <class Closure>
class RepeatingTaskImpl final : public RepeatingTaskBase {
RepeatingTaskImpl(TaskQueueBase* task_queue,
TimeDelta first_delay,
Closure&& closure)
: RepeatingTaskBase(task_queue, first_delay),
closure_(std::forward<Closure>(closure)) {
typename std::result_of<decltype (&Closure::operator())(
TimeDelta RunClosure() override { return closure_(); }
typename std::remove_const<
typename std::remove_reference<Closure>::type>::type closure_;
} // namespace webrtc_repeating_task_impl
// Allows starting tasks that repeat themselves on a TaskQueue indefinately
// until they are stopped or the TaskQueue is destroyed. It allows starting and
// stopping multiple times, but you must stop one task before starting another
// and it can only be stopped when in the running state. The public interface is
// not thread safe.
class RepeatingTaskHandle {
RepeatingTaskHandle() = default;
~RepeatingTaskHandle() = default;
RepeatingTaskHandle(RepeatingTaskHandle&& other);
RepeatingTaskHandle& operator=(RepeatingTaskHandle&& other);
RepeatingTaskHandle(const RepeatingTaskHandle&) = delete;
RepeatingTaskHandle& operator=(const RepeatingTaskHandle&) = delete;
// Start can be used to start a task that will be reposted with a delay
// determined by the return value of the provided closure. The actual task is
// owned by the TaskQueue and will live until it has been stopped or the
// TaskQueue is destroyed. Note that this means that trying to stop the
// repeating task after the TaskQueue is destroyed is an error. However, it's
// perfectly fine to destroy the handle while the task is running, since the
// repeated task is owned by the TaskQueue.
template <class Closure>
static RepeatingTaskHandle Start(TaskQueueBase* task_queue,
Closure&& closure) {
auto repeating_task = absl::make_unique<
task_queue, TimeDelta::Zero(), std::forward<Closure>(closure));
auto* repeating_task_ptr = repeating_task.get();
return RepeatingTaskHandle(repeating_task_ptr);
// DelayedStart is equivalent to Start except that the first invocation of the
// closure will be delayed by the given amount.
template <class Closure>
static RepeatingTaskHandle DelayedStart(TaskQueueBase* task_queue,
TimeDelta first_delay,
Closure&& closure) {
auto repeating_task = absl::make_unique<
task_queue, first_delay, std::forward<Closure>(closure));
auto* repeating_task_ptr = repeating_task.get();
return RepeatingTaskHandle(repeating_task_ptr);
// Stops future invocations of the repeating task closure. Can only be called
// from the TaskQueue where the task is running. The closure is guaranteed to
// not be running after Stop() returns unless Stop() is called from the
// closure itself.
void Stop();
// Returns true if Start() or DelayedStart() was called most recently. Returns
// false initially and if Stop() or PostStop() was called most recently.
bool Running() const;
explicit RepeatingTaskHandle(
webrtc_repeating_task_impl::RepeatingTaskBase* repeating_task);
// Owned by the task queue.
webrtc_repeating_task_impl::RepeatingTaskBase* repeating_task_ = nullptr;
} // namespace webrtc