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Diffstat (limited to 'security/sandbox/chromium/base/task_runner.h')
| -rw-r--r-- | security/sandbox/chromium/base/task_runner.h | 154 |
1 files changed, 154 insertions, 0 deletions
diff --git a/security/sandbox/chromium/base/task_runner.h b/security/sandbox/chromium/base/task_runner.h new file mode 100644 index 000000000..6dd82ccac --- /dev/null +++ b/security/sandbox/chromium/base/task_runner.h @@ -0,0 +1,154 @@ +// 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_TASK_RUNNER_H_ +#define BASE_TASK_RUNNER_H_ + +#include <stddef.h> + +#include "base/base_export.h" +#include "base/callback_forward.h" +#include "base/memory/ref_counted.h" +#include "base/time/time.h" + +namespace tracked_objects { +class Location; +} // namespace tracked_objects + +namespace base { + +struct TaskRunnerTraits; + +// A TaskRunner is an object that runs posted tasks (in the form of +// Closure 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> { + public: + // Posts the given task to be run. Returns true if the task may be + // run at some point in the future, and false if the task definitely + // will not be run. + // + // Equivalent to PostDelayedTask(from_here, task, 0). + bool PostTask(const tracked_objects::Location& from_here, + const Closure& task); + + // Like PostTask, but tries to run the posted task only after + // |delay_ms| has passed. + // + // It is valid for an implementation to ignore |delay_ms|; that is, + // to have PostDelayedTask behave the same as PostTask. + virtual bool PostDelayedTask(const tracked_objects::Location& from_here, + const Closure& task, + base::TimeDelta delay) = 0; + + // Returns true if the current thread is a thread on which a task + // may be run, and false if no task will be run on the current + // thread. + // + // It is valid for an implementation to always return true, or in + // general to use 'true' as a default value. + virtual bool RunsTasksOnCurrentThread() const = 0; + + // Posts |task| on the current TaskRunner. On completion, |reply| + // is posted to the thread that called PostTaskAndReply(). Both + // |task| and |reply| are guaranteed to be deleted on the thread + // from which PostTaskAndReply() is invoked. This allows objects + // that must be deleted on the originating thread to be bound into + // the |task| and |reply| Closures. In particular, it can be useful + // to use WeakPtr<> in the |reply| Closure so that the reply + // operation can be canceled. See the following pseudo-code: + // + // class DataBuffer : public RefCountedThreadSafe<DataBuffer> { + // public: + // // Called to add data into a buffer. + // void AddData(void* buf, size_t length); + // ... + // }; + // + // + // class DataLoader : public SupportsWeakPtr<DataLoader> { + // public: + // void GetData() { + // scoped_refptr<DataBuffer> buffer = new DataBuffer(); + // target_thread_.task_runner()->PostTaskAndReply( + // FROM_HERE, + // base::Bind(&DataBuffer::AddData, buffer), + // base::Bind(&DataLoader::OnDataReceived, AsWeakPtr(), buffer)); + // } + // + // private: + // void OnDataReceived(scoped_refptr<DataBuffer> buffer) { + // // Do something with buffer. + // } + // }; + // + // + // Things to notice: + // * Results of |task| are shared with |reply| by binding a shared argument + // (a DataBuffer instance). + // * The DataLoader object has no special thread safety. + // * The DataLoader object can be deleted while |task| is still running, + // and the reply will cancel itself safely because it is bound to a + // WeakPtr<>. + bool PostTaskAndReply(const tracked_objects::Location& from_here, + const Closure& task, + const Closure& reply); + + protected: + friend struct TaskRunnerTraits; + + // Only the Windows debug build seems to need this: see + // http://crbug.com/112250. + friend class RefCountedThreadSafe<TaskRunner, TaskRunnerTraits>; + + TaskRunner(); + virtual ~TaskRunner(); + + // Called when this object should be destroyed. By default simply + // deletes |this|, but can be overridden to do something else, like + // delete on a certain thread. + virtual void OnDestruct() const; +}; + +struct BASE_EXPORT TaskRunnerTraits { + static void Destruct(const TaskRunner* task_runner); +}; + +} // namespace base + +#endif // BASE_TASK_RUNNER_H_ |