Add helper KeepRefUntilDone

webrtc/base/release_when_done_callback.h

Index: webrtc/base/release_when_done_callback.h
diff --git a/webrtc/base/release_when_done_callback.h b/webrtc/base/release_when_done_callback.h
new file mode 100644
index 0000000000000000000000000000000000000000..e764e257eb4bbb10158cbfa0d8fd9f4e92f8ea45
--- /dev/null
+++ b/webrtc/base/release_when_done_callback.h
@@ -0,0 +1,36 @@
+/*
+ *  Copyright 2004 The WebRTC Project Authors. All rights reserved.

[mflodman, 2015/11/30 08:45:10]

s/2004/2015

[perkj_webrtc, 2015/11/30 12:54:19]

Done.

+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_BASE_RELEASE_WHEN_DONE_CALLBACK_H_
+#define WEBRTC_BASE_RELEASE_WHEN_DONE_CALLBACK_H_
+
+#include "webrtc/base/bind.h"
+#include "webrtc/base/callback.h"
+#include "webrtc/base/scoped_ref_ptr.h"
+
+namespace rtc {
+
+namespace impl {
+template <class T>
+void ReleaseRef(const scoped_refptr<T>& object) {}

[magjed_webrtc, 2015/11/30 09:22:17]

Should this be a static function?

[perkj_webrtc, 2015/11/30 12:54:19]

Done.

+}  // namespace impl
+
+// ReleaseWhenDoneCallback keeps a reference to |object| until the returned
+// callback goes out of scope. If the returned callback is copied, the
+// reference will be released when the last callback goes out of scope.
+template <class ObjectT>
+Callback0<void> ReleaseWhenDoneCallback(ObjectT* object) {

[tommi, 2015/11/30 08:45:51]

What's the difference between this implementation and something like:

ReleaseWhenDoneCallback(ObjectT* object) {
  object->AddRef();
  return rtc::Bind(&ObjectT::Release, object);
}

Actually, the name ReleaseWhenDoneCallback name kinda indicates that the
function will only Release and not AddRef.  What about KeepRefUntilDone?

[magjed_webrtc, 2015/11/30 09:22:17]

The argument type should be const scoped_refptr<ObjectT>&.

[magjed_webrtc, 2015/11/30 09:22:17]

ditto: Should this be a static function?

[perkj_webrtc, 2015/11/30 12:54:19]

Renamed.

The difference would be that the callback can in theory be executed mulitple
times.
ie 
cb = ReleaseWhenDoneCallback();
cb()  --> releases a ref
cb()  --> releases another ref...

[perkj_webrtc, 2015/11/30 12:54:19]

Done.

+  return rtc::Bind(&impl::ReleaseRef<ObjectT>, scoped_refptr<ObjectT>(object));
+}
+
+}  // namespace rtc
+
+
+#endif  // WEBRTC_BASE_RELEASE_WHEN_DONE_CALLBACK_H_