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// Copyright 2017 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef MEDIA_MIDI_TASK_SERVICE_H_
#define MEDIA_MIDI_TASK_SERVICE_H_
#include <memory>
#include <vector>
#include "base/callback_forward.h"
#include "base/compiler_specific.h"
#include "base/macros.h"
#include "base/memory/ref_counted.h"
#include "base/sequence_checker.h"
#include "base/single_thread_task_runner.h"
#include "base/synchronization/condition_variable.h"
#include "base/synchronization/lock.h"
#include "base/thread_annotations.h"
#include "base/threading/thread.h"
#include "base/time/time.h"
#include "media/midi/midi_export.h"
namespace midi {
// TaskService manages TaskRunners that can be used in midi and provides
// functionalities to ensure thread safety.
class MIDI_EXPORT TaskService final {
public:
using RunnerId = size_t;
using InstanceId = int64_t;
static constexpr RunnerId kDefaultRunnerId = 0;
TaskService();
~TaskService();
// Issues an InstanceId internally to post tasks via PostBoundTask() and
// PostDelayedBoundTask() with the InstanceId. Once UnbindInstance() is
// called, tasks posted via these methods with unbind InstanceId won't be
// invoked any more.
// Returns true if call is bound or unbound correctly. Otherwise returns
// false, that happens when the BindInstance() is called twice without
// unbinding the previous instance, or the UnbindInstance() is called without
// any successful BindInstance() call.
bool BindInstance() WARN_UNUSED_RESULT;
bool UnbindInstance() WARN_UNUSED_RESULT;
// Checks if the current thread belongs to the specified runner.
bool IsOnTaskRunner(RunnerId runner_id);
// Posts a task to run on a specified TaskRunner. |runner_id| should be a
// positive number that represents a dedicated thread on that |task| will run.
// |task| will run even without a bound instance.
void PostStaticTask(RunnerId runner_id, base::OnceClosure task);
// Posts a task to run on a specified TaskRunner, and ensures that the bound
// instance should not quit UnbindInstance() while a bound task is running.
// |runner_id| should be |kDefaultRunnerId| or a positive number. If
// |kDefaultRunnerId| is specified, the task runs on the thread on which
// BindInstance() was called.
void PostBoundTask(RunnerId runner, base::OnceClosure task);
void PostBoundDelayedTask(RunnerId runner_id,
base::OnceClosure task,
base::TimeDelta delay);
void OverflowInstanceIdForTesting();
private:
static constexpr TaskService::InstanceId kInvalidInstanceId = -1;
// Returns a SingleThreadTaskRunner reference. Each TaskRunner will be
// constructed on demand.
scoped_refptr<base::SingleThreadTaskRunner> GetTaskRunner(RunnerId runner_id);
// Helps to run a posted bound task on TaskRunner safely.
void RunTask(InstanceId instance_id,
RunnerId runner_id,
base::OnceClosure task);
// Returns true if |instance_id| is equal to |bound_instance_id_|.
bool IsInstanceIdStillBound(InstanceId instance_id);
// Holds InstanceId for the next bound instance, accessed on the BindInstance
// call thread without any protection.
InstanceId next_instance_id_ = kInvalidInstanceId;
// Keeps a TaskRunner for the thread that calls BindInstance() as a default
// task runner to run posted tasks.
scoped_refptr<base::SingleThreadTaskRunner> default_task_runner_
GUARDED_BY(lock_);
// Holds threads to host SingleThreadTaskRunners.
std::vector<std::unique_ptr<base::Thread>> threads_ GUARDED_BY(lock_);
// Holds InstanceId for the current bound instance.
InstanceId bound_instance_id_ GUARDED_BY(lock_) = kInvalidInstanceId;
base::Lock lock_;
// Signalled when the number of tasks in flight is 0 and ensures that
// UnbindInstance() does not return until all tasks have completed.
base::ConditionVariable no_tasks_in_flight_cv_
GUARDED_BY(tasks_in_flight_lock_);
// Number of tasks in flight.
int tasks_in_flight_ GUARDED_BY(tasks_in_flight_lock_) = 0;
base::Lock tasks_in_flight_lock_;
// Verifies all UnbindInstance() calls occur on the same sequence as
// BindInstance().
SEQUENCE_CHECKER(instance_binding_sequence_checker_);
DISALLOW_COPY_AND_ASSIGN(TaskService);
};
} // namespace midi
#endif // MEDIA_MIDI_TASK_SERVICE_H_
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