1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/security/sandbox/chromium/base/task_runner.h Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,153 @@
1.4 +// Copyright (c) 2012 The Chromium Authors. All rights reserved.
1.5 +// Use of this source code is governed by a BSD-style license that can be
1.6 +// found in the LICENSE file.
1.7 +
1.8 +#ifndef BASE_TASK_RUNNER_H_
1.9 +#define BASE_TASK_RUNNER_H_
1.10 +
1.11 +#include "base/base_export.h"
1.12 +#include "base/basictypes.h"
1.13 +#include "base/callback_forward.h"
1.14 +#include "base/memory/ref_counted.h"
1.15 +#include "base/time/time.h"
1.16 +
1.17 +namespace tracked_objects {
1.18 +class Location;
1.19 +} // namespace tracked_objects
1.20 +
1.21 +namespace base {
1.22 +
1.23 +struct TaskRunnerTraits;
1.24 +
1.25 +// A TaskRunner is an object that runs posted tasks (in the form of
1.26 +// Closure objects). The TaskRunner interface provides a way of
1.27 +// decoupling task posting from the mechanics of how each task will be
1.28 +// run. TaskRunner provides very weak guarantees as to how posted
1.29 +// tasks are run (or if they're run at all). In particular, it only
1.30 +// guarantees:
1.31 +//
1.32 +// - Posting a task will not run it synchronously. That is, no
1.33 +// Post*Task method will call task.Run() directly.
1.34 +//
1.35 +// - Increasing the delay can only delay when the task gets run.
1.36 +// That is, increasing the delay may not affect when the task gets
1.37 +// run, or it could make it run later than it normally would, but
1.38 +// it won't make it run earlier than it normally would.
1.39 +//
1.40 +// TaskRunner does not guarantee the order in which posted tasks are
1.41 +// run, whether tasks overlap, or whether they're run on a particular
1.42 +// thread. Also it does not guarantee a memory model for shared data
1.43 +// between tasks. (In other words, you should use your own
1.44 +// synchronization/locking primitives if you need to share data
1.45 +// between tasks.)
1.46 +//
1.47 +// Implementations of TaskRunner should be thread-safe in that all
1.48 +// methods must be safe to call on any thread. Ownership semantics
1.49 +// for TaskRunners are in general not clear, which is why the
1.50 +// interface itself is RefCountedThreadSafe.
1.51 +//
1.52 +// Some theoretical implementations of TaskRunner:
1.53 +//
1.54 +// - A TaskRunner that uses a thread pool to run posted tasks.
1.55 +//
1.56 +// - A TaskRunner that, for each task, spawns a non-joinable thread
1.57 +// to run that task and immediately quit.
1.58 +//
1.59 +// - A TaskRunner that stores the list of posted tasks and has a
1.60 +// method Run() that runs each runnable task in random order.
1.61 +class BASE_EXPORT TaskRunner
1.62 + : public RefCountedThreadSafe<TaskRunner, TaskRunnerTraits> {
1.63 + public:
1.64 + // Posts the given task to be run. Returns true if the task may be
1.65 + // run at some point in the future, and false if the task definitely
1.66 + // will not be run.
1.67 + //
1.68 + // Equivalent to PostDelayedTask(from_here, task, 0).
1.69 + bool PostTask(const tracked_objects::Location& from_here,
1.70 + const Closure& task);
1.71 +
1.72 + // Like PostTask, but tries to run the posted task only after
1.73 + // |delay_ms| has passed.
1.74 + //
1.75 + // It is valid for an implementation to ignore |delay_ms|; that is,
1.76 + // to have PostDelayedTask behave the same as PostTask.
1.77 + virtual bool PostDelayedTask(const tracked_objects::Location& from_here,
1.78 + const Closure& task,
1.79 + base::TimeDelta delay) = 0;
1.80 +
1.81 + // Returns true if the current thread is a thread on which a task
1.82 + // may be run, and false if no task will be run on the current
1.83 + // thread.
1.84 + //
1.85 + // It is valid for an implementation to always return true, or in
1.86 + // general to use 'true' as a default value.
1.87 + virtual bool RunsTasksOnCurrentThread() const = 0;
1.88 +
1.89 + // Posts |task| on the current TaskRunner. On completion, |reply|
1.90 + // is posted to the thread that called PostTaskAndReply(). Both
1.91 + // |task| and |reply| are guaranteed to be deleted on the thread
1.92 + // from which PostTaskAndReply() is invoked. This allows objects
1.93 + // that must be deleted on the originating thread to be bound into
1.94 + // the |task| and |reply| Closures. In particular, it can be useful
1.95 + // to use WeakPtr<> in the |reply| Closure so that the reply
1.96 + // operation can be canceled. See the following pseudo-code:
1.97 + //
1.98 + // class DataBuffer : public RefCountedThreadSafe<DataBuffer> {
1.99 + // public:
1.100 + // // Called to add data into a buffer.
1.101 + // void AddData(void* buf, size_t length);
1.102 + // ...
1.103 + // };
1.104 + //
1.105 + //
1.106 + // class DataLoader : public SupportsWeakPtr<DataLoader> {
1.107 + // public:
1.108 + // void GetData() {
1.109 + // scoped_refptr<DataBuffer> buffer = new DataBuffer();
1.110 + // target_thread_.message_loop_proxy()->PostTaskAndReply(
1.111 + // FROM_HERE,
1.112 + // base::Bind(&DataBuffer::AddData, buffer),
1.113 + // base::Bind(&DataLoader::OnDataReceived, AsWeakPtr(), buffer));
1.114 + // }
1.115 + //
1.116 + // private:
1.117 + // void OnDataReceived(scoped_refptr<DataBuffer> buffer) {
1.118 + // // Do something with buffer.
1.119 + // }
1.120 + // };
1.121 + //
1.122 + //
1.123 + // Things to notice:
1.124 + // * Results of |task| are shared with |reply| by binding a shared argument
1.125 + // (a DataBuffer instance).
1.126 + // * The DataLoader object has no special thread safety.
1.127 + // * The DataLoader object can be deleted while |task| is still running,
1.128 + // and the reply will cancel itself safely because it is bound to a
1.129 + // WeakPtr<>.
1.130 + bool PostTaskAndReply(const tracked_objects::Location& from_here,
1.131 + const Closure& task,
1.132 + const Closure& reply);
1.133 +
1.134 + protected:
1.135 + friend struct TaskRunnerTraits;
1.136 +
1.137 + // Only the Windows debug build seems to need this: see
1.138 + // http://crbug.com/112250.
1.139 + friend class RefCountedThreadSafe<TaskRunner, TaskRunnerTraits>;
1.140 +
1.141 + TaskRunner();
1.142 + virtual ~TaskRunner();
1.143 +
1.144 + // Called when this object should be destroyed. By default simply
1.145 + // deletes |this|, but can be overridden to do something else, like
1.146 + // delete on a certain thread.
1.147 + virtual void OnDestruct() const;
1.148 +};
1.149 +
1.150 +struct BASE_EXPORT TaskRunnerTraits {
1.151 + static void Destruct(const TaskRunner* task_runner);
1.152 +};
1.153 +
1.154 +} // namespace base
1.155 +
1.156 +#endif // BASE_TASK_RUNNER_H_
