Add APIs to protect critical tasks on iOS.

base/ios/scoped_critical_action.mm

Index: base/ios/scoped_critical_action.mm
diff --git a/base/ios/scoped_critical_action.mm b/base/ios/scoped_critical_action.mm
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index 0000000000000000000000000000000000000000..28f9df7b6ff836214fcbd5c53cadefde348b74c4
--- /dev/null
+++ b/base/ios/scoped_critical_action.mm
@@ -0,0 +1,49 @@
+// 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.
+
+#include "base/ios/scoped_critical_action.h"
+
+#include "base/logging.h"
+#include "base/synchronization/lock.h"
+
+#import <UIKit/UIKit.h>

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

C system includes before project includes, with the exception of this file’s
associated header (scoped_critical_action.h), which should be first.

You got the order right in critical_closure_ios.mm.

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

Done.

+
+namespace base {
+namespace ios {
+
+// This implementation calls |beginBackgroundTaskWithExpirationHandler:| when
+// instantiated and |endBackgroundTask:| when destroyed, creating a scope whose
+// execution will continue (temporarily) even after the app is backgrounded.
+ScopedCriticalAction::ScopedCriticalAction() {
+  background_task_id_ = [[UIApplication sharedApplication]

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

This function returns a UIBackgroundTaskIdentifier, so why did you make
background_task_id_ an unsigned int? It should be a UIBackgroundTaskIdentifier.
If you need to #import <UIKit/UIKit.h> in the .h to get the type declaration,
that’s fine.

[stuartmorgan, 2012/08/01 04:31:55]

Except it isn't, which is why we did this. It makes it impossible to use
ScopedCriticalAction in .cc files (which is almost always where we end up
needing to use it)

[Mark Mentovai, 2012/08/01 13:50:42]

stuartmorgan wrote:
Then the use of the unexpected type requires a comment (and if it were used in
more than one spot, a typedef would be helpful too).

+      beginBackgroundTaskWithExpirationHandler:^{
+        DLOG(WARNING) << "Background task with id " << background_task_id_
+                      << " expired.";
+        // Note if |endBackgroundTask:| is not called for each task before time
+        // expires, the system kills the application.
+        EndBackgroundTask();
+      }];
+  VLOG(3) << "Beginning background task with id " << background_task_id_;

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

The docs say something about UIBackgroundTaskInvalid being returned here. Do you
want to handle that?

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

There is no much we can do in this case; a warning in logged here, also made
some changes in |EndBackgroundTask()|.
On 2012/07/31 23:16:33, Mark Mentovai wrote:

+}
+
+ScopedCriticalAction::~ScopedCriticalAction() {
+  EndBackgroundTask();
+}
+
+void ScopedCriticalAction::EndBackgroundTask() {
+  UIBackgroundTaskIdentifier task_id;
+  {
+    AutoLock lockScope(id_lock_);
+    task_id = background_task_id_;
+    background_task_id_ = UIBackgroundTaskInvalid;
+  }
+  if (task_id == UIBackgroundTaskInvalid)
+    return;
+
+  VLOG(3) << "Ending background task with id " << task_id;
+  [[UIApplication sharedApplication] endBackgroundTask:task_id];
+}
+
+}  // namespace ios
+}  // namespace base