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* Copyright 2016 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 <stdint.h>
#include <memory>
#include <utility>
#include "absl/memory/memory.h"
#include "api/task_queue/queued_task.h"
#include "api/task_queue/task_queue_base.h"
#include "api/task_queue/task_queue_factory.h"
#include "rtc_base/constructor_magic.h"
#include "rtc_base/system/rtc_export.h"
#include "rtc_base/task_utils/to_queued_task.h"
#include "rtc_base/thread_annotations.h"
namespace rtc {
// Implements a task queue that asynchronously executes tasks in a way that
// guarantees that they're executed in FIFO order and that tasks never overlap.
// Tasks may always execute on the same worker thread and they may not.
// To DCHECK that tasks are executing on a known task queue, use IsCurrent().
// Here are some usage examples:
// 1) Asynchronously running a lambda:
// class MyClass {
// ...
// TaskQueue queue_("MyQueue");
// };
// void MyClass::StartWork() {
// queue_.PostTask([]() { Work(); });
// ...
// 2) Posting a custom task on a timer. The task posts itself again after
// every running:
// class TimerTask : public QueuedTask {
// public:
// TimerTask() {}
// private:
// bool Run() override {
// ++count_;
// TaskQueueBase::Current()->PostDelayedTask(
// absl::WrapUnique(this), 1000);
// // Ownership has been transferred to the next occurance,
// // so return false to prevent from being deleted now.
// return false;
// }
// int count_ = 0;
// };
// ...
// queue_.PostDelayedTask(std::make_unique<TimerTask>(), 1000);
// For more examples, see
// A note on destruction:
// When a TaskQueue is deleted, pending tasks will not be executed but they will
// be deleted. The deletion of tasks may happen asynchronously after the
// TaskQueue itself has been deleted or it may happen synchronously while the
// TaskQueue instance is being deleted. This may vary from one OS to the next
// so assumptions about lifetimes of pending tasks should not be made.
// TaskQueue priority levels. On some platforms these will map to thread
// priorities, on others such as Mac and iOS, GCD queue priorities.
using Priority = ::webrtc::TaskQueueFactory::Priority;
explicit TaskQueue(std::unique_ptr<webrtc::TaskQueueBase,
webrtc::TaskQueueDeleter> task_queue);
// Used for DCHECKing the current queue.
bool IsCurrent() const;
// Returns non-owning pointer to the task queue implementation.
webrtc::TaskQueueBase* Get() { return impl_; }
// TODO(tommi): For better debuggability, implement RTC_FROM_HERE.
// Ownership of the task is passed to PostTask.
void PostTask(std::unique_ptr<webrtc::QueuedTask> task);
// Schedules a task to execute a specified number of milliseconds from when
// the call is made. The precision should be considered as "best effort"
// and in some cases, such as on Windows when all high precision timers have
// been used up, can be off by as much as 15 millseconds (although 8 would be
// more likely). This can be mitigated by limiting the use of delayed tasks.
void PostDelayedTask(std::unique_ptr<webrtc::QueuedTask> task,
uint32_t milliseconds);
// std::enable_if is used here to make sure that calls to PostTask() with
// std::unique_ptr<SomeClassDerivedFromQueuedTask> would not end up being
// caught by this template.
template <class Closure,
typename std::enable_if<!std::is_convertible<
std::unique_ptr<webrtc::QueuedTask>>::value>::type* = nullptr>
void PostTask(Closure&& closure) {
// See documentation above for performance expectations.
template <class Closure,
typename std::enable_if<!std::is_convertible<
std::unique_ptr<webrtc::QueuedTask>>::value>::type* = nullptr>
void PostDelayedTask(Closure&& closure, uint32_t milliseconds) {
webrtc::TaskQueueBase* const impl_;
} // namespace rtc