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// Copyright (c) 2012 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 BASE_THREADING_WORKER_POOL_H_
#define BASE_THREADING_WORKER_POOL_H_
#include "base/base_export.h"
#include "base/callback_forward.h"
#include "base/memory/ref_counted.h"
class Task;
namespace tracked_objects {
class Location;
} // namespace tracked_objects
namespace base {
class TaskRunner;
// This is a facility that runs tasks that don't require a specific thread or
// a message loop.
//
// WARNING: This shouldn't be used unless absolutely necessary. Typically
// (without calling ShutDownCleanly()), we don't wait for the worker pool
// threads to finish on shutdown, so the tasks running inside the pool must be
// extremely careful about other objects they access (MessageLoops, Singletons,
// etc). During shutdown these object may no longer exist.
class BASE_EXPORT WorkerPool {
public:
// This function posts |task| to run on a worker thread. |task_is_slow|
// should be used for tasks that will take a long time to execute. Returns
// false if |task| could not be posted to a worker thread. Regardless of
// return value, ownership of |task| is transferred to the worker pool.
static bool PostTask(const tracked_objects::Location& from_here,
const base::Closure& task, bool task_is_slow);
// Just like TaskRunner::PostTaskAndReply, except the destination
// for |task| is a worker thread and you can specify |task_is_slow| just
// like you can for PostTask above.
static bool PostTaskAndReply(const tracked_objects::Location& from_here,
const Closure& task,
const Closure& reply,
bool task_is_slow);
// Return true if the current thread is one that this WorkerPool runs tasks
// on. (Note that if the Windows worker pool is used without going through
// this WorkerPool interface, RunsTasksOnCurrentThread would return false on
// those threads.)
static bool RunsTasksOnCurrentThread();
// Get a TaskRunner wrapper which posts to the WorkerPool using the given
// |task_is_slow| behavior.
static const scoped_refptr<TaskRunner>& GetTaskRunner(bool task_is_slow);
// Blocks until all worker threads quit cleanly. Please note that it ensures
// that no worker threads are running after the method returns, but it doesn't
// guarantee to process all queued pending tasks. This method may take a long
// time. Please don't use it unless absolutely necessary, e.g., when we want
// to unload the library containing the worker pool before process shutdown.
static void ShutDownCleanly();
};
} // namespace base
#endif // BASE_THREADING_WORKER_POOL_H_
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