task_runner.h | Explore in Territory

// Copyright 2012 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_TASK_RUNNER_H_
#define BASE_TASK_TASK_RUNNER_H_

#include <stddef.h>

#include "base/base_export.h"
#include "base/check.h"
#include "base/functional/bind.h"
#include "base/functional/callback.h"
#include "base/functional/callback_helpers.h"
#include "base/location.h"
#include "base/memory/ref_counted.h"
#include "base/task/post_task_and_reply_with_result_internal.h"

namespace base {

struct TaskRunnerTraits;
class TimeDelta;

// A TaskRunner is an object that runs posted tasks (in the form of
// OnceClosure objects).  The TaskRunner interface provides a way of
// decoupling task posting from the mechanics of how each task will be
// run.  TaskRunner provides very weak guarantees as to how posted
// tasks are run (or if they're run at all).  In particular, it only
// guarantees:
//
//   - Posting a task will not run it synchronously.  That is, no
//     Post*Task method will call task.Run() directly.
//
//   - Increasing the delay can only delay when the task gets run.
//     That is, increasing the delay may not affect when the task gets
//     run, or it could make it run later than it normally would, but
//     it won't make it run earlier than it normally would.
//
// TaskRunner does not guarantee the order in which posted tasks are
// run, whether tasks overlap, or whether they're run on a particular
// thread.  Also it does not guarantee a memory model for shared data
// between tasks.  (In other words, you should use your own
// synchronization/locking primitives if you need to share data
// between tasks.)
//
// Implementations of TaskRunner should be thread-safe in that all
// methods must be safe to call on any thread.  Ownership semantics
// for TaskRunners are in general not clear, which is why the
// interface itself is RefCountedThreadSafe.
//
// Some theoretical implementations of TaskRunner:
//
//   - A TaskRunner that uses a thread pool to run posted tasks.
//
//   - A TaskRunner that, for each task, spawns a non-joinable thread
//     to run that task and immediately quit.
//
//   - A TaskRunner that stores the list of posted tasks and has a
//     method Run() that runs each runnable task in random order.
class BASE_EXPORT TaskRunner
    : public RefCountedThreadSafe<TaskRunner, TaskRunnerTraits> { … };

struct BASE_EXPORT TaskRunnerTraits { … };

}  // namespace base

#endif  // BASE_TASK_TASK_RUNNER_H_
chromium/base/task/task_runner.h
