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