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// Copyright 2013 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_TASK_DEFERRED_SEQUENCED_TASK_RUNNER_H_
#define BASE_TASK_DEFERRED_SEQUENCED_TASK_RUNNER_H_
#include <vector>
#include "base/base_export.h"
#include "base/compiler_specific.h"
#include "base/functional/callback.h"
#include "base/synchronization/lock.h"
#include "base/task/sequenced_task_runner.h"
#include "base/threading/platform_thread.h"
#include "base/time/time.h"
namespace base {
// A DeferredSequencedTaskRunner is a subclass of SequencedTaskRunner that
// queues up all requests until the first call to Start() is issued.
// DeferredSequencedTaskRunner may be created in two ways:
// . with an explicit SequencedTaskRunner that the events are flushed to
// . without a SequencedTaskRunner. In this configuration the
// SequencedTaskRunner is supplied in StartWithTaskRunner().
class BASE_EXPORT DeferredSequencedTaskRunner : public SequencedTaskRunner {
public:
explicit DeferredSequencedTaskRunner(
scoped_refptr<SequencedTaskRunner> target_runner);
// Use this constructor when you don't have the target SequencedTaskRunner.
// When using this call StartWithTaskRunner().
DeferredSequencedTaskRunner();
DeferredSequencedTaskRunner(const DeferredSequencedTaskRunner&) = delete;
DeferredSequencedTaskRunner& operator=(const DeferredSequencedTaskRunner&) =
delete;
// TaskRunner implementation
bool PostDelayedTask(const Location& from_here,
OnceClosure task,
TimeDelta delay) override;
// SequencedTaskRunner implementation
bool RunsTasksInCurrentSequence() const override;
bool PostNonNestableDelayedTask(const Location& from_here,
OnceClosure task,
TimeDelta delay) override;
// Start the execution - posts all queued tasks to the target executor. The
// deferred tasks are posted with their initial delay, meaning that the task
// execution delay is actually measured from Start.
// Fails when called a second time.
void Start();
// Same as Start(), but must be used with the no-arg constructor.
void StartWithTaskRunner(
scoped_refptr<SequencedTaskRunner> target_task_runner);
// Returns true if task execution has been started.
bool Started() const;
private:
struct DeferredTask {
DeferredTask();
DeferredTask(DeferredTask&& other);
~DeferredTask();
DeferredTask& operator=(DeferredTask&& other);
Location posted_from;
OnceClosure task;
// The delay this task was initially posted with.
TimeDelta delay;
bool is_non_nestable;
};
~DeferredSequencedTaskRunner() override;
// Both variants of Start() call into this.
void StartImpl();
// Creates a |Task| object and adds it to |deferred_tasks_queue_|.
void QueueDeferredTask(const Location& from_here,
OnceClosure task,
TimeDelta delay,
bool is_non_nestable);
mutable Lock lock_;
const PlatformThreadId created_thread_id_;
// An atomic pointer that allows to call task_runner methods without lock.
// It's possible because the pointer starts as null, is set to a non-null
// value only once, and is never changed again.
// This is used to implement a lock-free RunsTasksInCurrentSequence method.
std::atomic<SequencedTaskRunner*> task_runner_atomic_ptr_{nullptr};
bool started_ GUARDED_BY(lock_) = false;
scoped_refptr<SequencedTaskRunner> target_task_runner_ GUARDED_BY(lock_);
std::vector<DeferredTask> deferred_tasks_queue_ GUARDED_BY(lock_);
};
} // namespace base
#endif // BASE_TASK_DEFERRED_SEQUENCED_TASK_RUNNER_H_
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