Add APIs to protect critical tasks on iOS.

base/ios/scoped_critical_action.h

+// 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_IOS_SCOPED_CRITICAL_ACTION_H_
+#define BASE_IOS_SCOPED_CRITICAL_ACTION_H_
+
+#include "base/synchronization/lock.h"
+
+namespace base {
+namespace ios {
+
+// This class allows the application to continue to run for a period of time
+// after it transitions to the background. The construction of an instance of
+// this class marks the beginning of a task that needs background running time
+// when the application is moved to the background and the destruction marks the
+// end of such a task.
+//
+// This class should be used at times where leaving a task unfinished might be
+// detrimental to user experience. For example, it should be used to ensure that
+// the application has enough time to save important data or at least attempt to
+// save such data.
+class ScopedCriticalAction {
+ public:
+  ScopedCriticalAction();
+  ~ScopedCriticalAction();
+
+ private:
+  // Informs the OS that the background task has completed.
+  void EndBackgroundTask();
+
+  unsigned int background_task_id_;

[Mark Mentovai, 2012/07/31 23:16:33]

What does this do? Comment it.

[Chen Yu, 2012/08/01 11:26:13]

Done.

+  Lock id_lock_;

[Mark Mentovai, 2012/07/31 23:16:33]

What does this protect? Comment it. If it protects background_task_id_, it
should be named background_task_id_lock_ to be self-documenting (and in that
case, you need not provide a comment unless there’s something non-obvious about
the way the lock is used.)

[Chen Yu, 2012/08/01 11:26:13]

Done.

+
+  DISALLOW_COPY_AND_ASSIGN(ScopedCriticalAction);
+};
+
+}  // namespace ios
+}  // namespace base
+
+#endif  // BASE_IOS_SCOPED_CRITICAL_ACTION_H_