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/*
* Copyright 2020 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.
*/
#ifndef RTC_BASE_TASK_UTILS_PENDING_TASK_SAFETY_FLAG_H_
#define RTC_BASE_TASK_UTILS_PENDING_TASK_SAFETY_FLAG_H_
#include "api/scoped_refptr.h"
#include "rtc_base/checks.h"
#include "rtc_base/ref_count.h"
#include "rtc_base/synchronization/sequence_checker.h"
namespace webrtc {
// Use this flag to drop pending tasks that have been posted to the "main"
// thread/TQ and end up running after the owning instance has been
// deleted. The owning instance signals deletion by calling SetNotAlive() from
// its destructor.
//
// When posting a task, post a copy (capture by-value in a lambda) of the flag
// instance and before performing the work, check the |alive()| state. Abort if
// alive() returns |false|:
//
// // Running outside of the main thread.
// my_task_queue_->PostTask(ToQueuedTask(
// [safety = pending_task_safety_flag_, this]() {
// // Now running on the main thread.
// if (!safety->alive())
// return;
// MyMethod();
// }));
//
// Or implicitly by letting ToQueuedTask do the checking:
//
// // Running outside of the main thread.
// my_task_queue_->PostTask(ToQueuedTask(pending_task_safety_flag_,
// [this]() { MyMethod(); }));
//
// Note that checking the state only works on the construction/destruction
// thread of the ReceiveStatisticsProxy instance.
class PendingTaskSafetyFlag : public rtc::RefCountInterface {
public:
static rtc::scoped_refptr<PendingTaskSafetyFlag> Create();
~PendingTaskSafetyFlag() = default;
void SetNotAlive();
bool alive() const;
protected:
PendingTaskSafetyFlag() = default;
private:
bool alive_ = true;
SequenceChecker main_sequence_;
};
// Makes using PendingTaskSafetyFlag very simple. Automatic PTSF creation
// and signalling of destruction when the ScopedTaskSafety instance goes out
// of scope.
// Should be used by the class that wants tasks dropped after destruction.
// Requirements are that the instance be constructed and destructed on
// the same thread as the potentially dropped tasks would be running on.
class ScopedTaskSafety {
public:
ScopedTaskSafety() = default;
~ScopedTaskSafety() { flag_->SetNotAlive(); }
// Returns a new reference to the safety flag.
rtc::scoped_refptr<PendingTaskSafetyFlag> flag() const { return flag_; }
private:
rtc::scoped_refptr<PendingTaskSafetyFlag> flag_ =
PendingTaskSafetyFlag::Create();
};
} // namespace webrtc
#endif // RTC_BASE_TASK_UTILS_PENDING_TASK_SAFETY_FLAG_H_