The Tor Browser: comparison security/sandbox/chromium/base/task

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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_TASK_RUNNER_H_
+#define BASE_TASK_RUNNER_H_
+#include "base/base_export.h"
+#include "base/basictypes.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_.message_loop_proxy()->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_

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comparison: security/sandbox/chromium/base/task_runner.h

security/sandbox/chromium/base/task_runner.h