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76d30a507d
Bug: none Change-Id: Iff9bf0e1965663581ba34f45f71b9cf23032af7a Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/207164 Reviewed-by: Tommi <tommi@webrtc.org> Commit-Queue: Harald Alvestrand <hta@webrtc.org> Cr-Commit-Position: refs/heads/master@{#33250}
107 lines
3.5 KiB
C++
107 lines
3.5 KiB
C++
/*
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* Copyright 2020 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_UTILS_PENDING_TASK_SAFETY_FLAG_H_
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#define RTC_BASE_TASK_UTILS_PENDING_TASK_SAFETY_FLAG_H_
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#include "api/scoped_refptr.h"
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#include "api/sequence_checker.h"
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#include "rtc_base/checks.h"
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#include "rtc_base/ref_count.h"
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#include "rtc_base/system/no_unique_address.h"
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namespace webrtc {
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// The PendingTaskSafetyFlag and the ScopedTaskSafety are designed to address
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// the issue where you have a task to be executed later that has references,
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// but cannot guarantee that the referenced object is alive when the task is
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// executed.
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// This mechanism can be used with tasks that are created and destroyed
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// on a single thread / task queue, and with tasks posted to the same
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// thread/task queue, but tasks can be posted from any thread/TQ.
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// Typical usage:
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// When posting a task, post a copy (capture by-value in a lambda) of the flag
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// reference and before performing the work, check the |alive()| state. Abort if
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// alive() returns |false|:
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//
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// class ExampleClass {
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// ....
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// my_task_queue_->PostTask(ToQueuedTask(
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// [safety = pending_task_safety_flag_, this]() {
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// // Now running on the main thread.
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// if (!safety->alive())
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// return;
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// MyMethod();
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// }));
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// ....
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// ~ExampleClass() {
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// pending_task_safety_flag_->SetNotAlive();
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// }
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// scoped_refptr<PendingTaskSafetyFlag> pending_task_safety_flag_
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// = PendingTaskSafetyFlag::Create();
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// }
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//
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// ToQueuedTask has an overload that makes this check automatic:
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//
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// my_task_queue_->PostTask(ToQueuedTask(pending_task_safety_flag_,
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// [this]() { MyMethod(); }));
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//
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class PendingTaskSafetyFlag : public rtc::RefCountInterface {
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public:
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static rtc::scoped_refptr<PendingTaskSafetyFlag> Create();
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~PendingTaskSafetyFlag() = default;
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void SetNotAlive();
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bool alive() const;
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protected:
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PendingTaskSafetyFlag() = default;
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private:
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bool alive_ = true;
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RTC_NO_UNIQUE_ADDRESS SequenceChecker main_sequence_;
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};
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// The ScopedTaskSafety makes using PendingTaskSafetyFlag very simple.
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// It does automatic PTSF creation and signalling of destruction when the
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// ScopedTaskSafety instance goes out of scope.
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//
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// ToQueuedTask has an overload that takes a ScopedTaskSafety too, so there
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// is no need to explicitly call the "flag" method.
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//
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// Example usage:
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//
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// my_task_queue->PostTask(ToQueuedTask(scoped_task_safety,
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// [this]() {
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// // task goes here
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// }
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//
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// This should be used by the class that wants tasks dropped after destruction.
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// The requirement is that the instance has to be constructed and destructed on
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// the same thread as the potentially dropped tasks would be running on.
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class ScopedTaskSafety {
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public:
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ScopedTaskSafety() = default;
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~ScopedTaskSafety() { flag_->SetNotAlive(); }
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// Returns a new reference to the safety flag.
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rtc::scoped_refptr<PendingTaskSafetyFlag> flag() const { return flag_; }
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private:
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rtc::scoped_refptr<PendingTaskSafetyFlag> flag_ =
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PendingTaskSafetyFlag::Create();
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};
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} // namespace webrtc
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#endif // RTC_BASE_TASK_UTILS_PENDING_TASK_SAFETY_FLAG_H_
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