15821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Copyright (c) 2012 The Chromium Authors. All rights reserved. 25821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Use of this source code is governed by a BSD-style license that can be 35821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// found in the LICENSE file. 45821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 55821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#ifndef BASE_TASK_RUNNER_H_ 65821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#define BASE_TASK_RUNNER_H_ 75821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 85821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/base_export.h" 95821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/basictypes.h" 105821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/callback_forward.h" 115821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#include "base/memory/ref_counted.h" 12eb525c5499e34cc9c4b825d6d9e75bb07cc06aceBen Murdoch#include "base/time/time.h" 135821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 145821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)namespace tracked_objects { 155821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)class Location; 165821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)} // namespace tracked_objects 175821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 185821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)namespace base { 195821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 205821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)struct TaskRunnerTraits; 215821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 225821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// A TaskRunner is an object that runs posted tasks (in the form of 235821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Closure objects). The TaskRunner interface provides a way of 245821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// decoupling task posting from the mechanics of how each task will be 255821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// run. TaskRunner provides very weak guarantees as to how posted 265821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// tasks are run (or if they're run at all). In particular, it only 275821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// guarantees: 285821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 295821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// - Posting a task will not run it synchronously. That is, no 305821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Post*Task method will call task.Run() directly. 315821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 325821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// - Increasing the delay can only delay when the task gets run. 335821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// That is, increasing the delay may not affect when the task gets 345821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// run, or it could make it run later than it normally would, but 355821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// it won't make it run earlier than it normally would. 365821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 375821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// TaskRunner does not guarantee the order in which posted tasks are 385821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// run, whether tasks overlap, or whether they're run on a particular 395821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// thread. Also it does not guarantee a memory model for shared data 405821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// between tasks. (In other words, you should use your own 415821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// synchronization/locking primitives if you need to share data 425821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// between tasks.) 435821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 445821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Implementations of TaskRunner should be thread-safe in that all 455821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// methods must be safe to call on any thread. Ownership semantics 465821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// for TaskRunners are in general not clear, which is why the 475821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// interface itself is RefCountedThreadSafe. 485821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 495821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// Some theoretical implementations of TaskRunner: 505821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 515821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// - A TaskRunner that uses a thread pool to run posted tasks. 525821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 535821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// - A TaskRunner that, for each task, spawns a non-joinable thread 545821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// to run that task and immediately quit. 555821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// 565821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// - A TaskRunner that stores the list of posted tasks and has a 575821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)// method Run() that runs each runnable task in random order. 585821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)class BASE_EXPORT TaskRunner 595821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) : public RefCountedThreadSafe<TaskRunner, TaskRunnerTraits> { 605821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) public: 615821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Posts the given task to be run. Returns true if the task may be 625821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // run at some point in the future, and false if the task definitely 635821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // will not be run. 645821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // 655821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Equivalent to PostDelayedTask(from_here, task, 0). 665821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) bool PostTask(const tracked_objects::Location& from_here, 675821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) const Closure& task); 685821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 695821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Like PostTask, but tries to run the posted task only after 705821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // |delay_ms| has passed. 715821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // 725821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // It is valid for an implementation to ignore |delay_ms|; that is, 735821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // to have PostDelayedTask behave the same as PostTask. 745821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) virtual bool PostDelayedTask(const tracked_objects::Location& from_here, 755821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) const Closure& task, 765821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) base::TimeDelta delay) = 0; 775821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 785821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Returns true if the current thread is a thread on which a task 795821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // may be run, and false if no task will be run on the current 805821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // thread. 815821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // 825821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // It is valid for an implementation to always return true, or in 835821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // general to use 'true' as a default value. 845821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) virtual bool RunsTasksOnCurrentThread() const = 0; 855821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 865821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Posts |task| on the current TaskRunner. On completion, |reply| 875821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // is posted to the thread that called PostTaskAndReply(). Both 885821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // |task| and |reply| are guaranteed to be deleted on the thread 895821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // from which PostTaskAndReply() is invoked. This allows objects 905821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // that must be deleted on the originating thread to be bound into 915821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // the |task| and |reply| Closures. In particular, it can be useful 925821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // to use WeakPtr<> in the |reply| Closure so that the reply 935821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // operation can be canceled. See the following pseudo-code: 945821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // 955821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // class DataBuffer : public RefCountedThreadSafe<DataBuffer> { 965821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // public: 975821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // // Called to add data into a buffer. 985821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // void AddData(void* buf, size_t length); 995821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // ... 1005821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // }; 1015821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // 1025821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // 1035821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // class DataLoader : public SupportsWeakPtr<DataLoader> { 1045821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // public: 1055821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // void GetData() { 1065821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // scoped_refptr<DataBuffer> buffer = new DataBuffer(); 1075821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // target_thread_.message_loop_proxy()->PostTaskAndReply( 1085821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // FROM_HERE, 1095821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // base::Bind(&DataBuffer::AddData, buffer), 1105821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // base::Bind(&DataLoader::OnDataReceived, AsWeakPtr(), buffer)); 1115821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // } 1125821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // 1135821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // private: 1145821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // void OnDataReceived(scoped_refptr<DataBuffer> buffer) { 1155821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // // Do something with buffer. 1165821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // } 1175821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // }; 1185821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // 1195821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // 1205821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Things to notice: 1215821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // * Results of |task| are shared with |reply| by binding a shared argument 1225821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // (a DataBuffer instance). 1235821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // * The DataLoader object has no special thread safety. 1245821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // * The DataLoader object can be deleted while |task| is still running, 1255821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // and the reply will cancel itself safely because it is bound to a 1265821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // WeakPtr<>. 1275821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) bool PostTaskAndReply(const tracked_objects::Location& from_here, 1285821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) const Closure& task, 1295821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) const Closure& reply); 1305821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1315821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) protected: 1325821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) friend struct TaskRunnerTraits; 1335821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1345821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Only the Windows debug build seems to need this: see 1355821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // http://crbug.com/112250. 1365821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) friend class RefCountedThreadSafe<TaskRunner, TaskRunnerTraits>; 1375821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1385821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) TaskRunner(); 1395821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) virtual ~TaskRunner(); 1405821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1415821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // Called when this object should be destroyed. By default simply 1425821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // deletes |this|, but can be overridden to do something else, like 1435821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) // delete on a certain thread. 1445821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) virtual void OnDestruct() const; 1455821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 1465821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1475821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)struct BASE_EXPORT TaskRunnerTraits { 1485821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) static void Destruct(const TaskRunner* task_runner); 1495821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)}; 1505821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1515821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)} // namespace base 1525821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles) 1535821806d5e7f356e8fa4b058a389a808ea183019Torne (Richard Coles)#endif // BASE_TASK_RUNNER_H_ 154