Add CopyOnWriteBuffer class

webrtc/base/copyonwritebuffer.cc

+/*
+ *  Copyright 2016 The WebRTC Project Authors. All rights reserved.
+ *
+ *  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.
+ */
+
+#include "webrtc/base/copyonwritebuffer.h"
+
+namespace rtc {
+
+CopyOnWriteBuffer::CopyOnWriteBuffer() {}
+
+CopyOnWriteBuffer::CopyOnWriteBuffer(const CopyOnWriteBuffer& buf)
+    : buffer_(buf.buffer_) {
+}
+
+CopyOnWriteBuffer::CopyOnWriteBuffer(CopyOnWriteBuffer&& buf)
+    : buffer_(buf.buffer_) {
+  // TODO(jbauch): use std::move once scoped_refptr supports it (issue 5556)
+  buf.buffer_ = nullptr;

[kwiberg-webrtc, 2016/02/20 06:43:32]

Use swap here too, just as in the move assignment. Otherwise you get an extra
incref+decref pair, which is not insignificant since IIRC the refcounts are
atomic.

You should end up with something like

  CopyOnWriteBuffer::CopyOnWriteBuffer(CopyOnWriteBuffer&& buf) {
    // commentz here!!!
    std::swap(buffer_, buf.buffer_);
  }

Note that since buffer_ starts out as null, you don't have to null buf.buffer_
afterwards.

[joachim, 2016/02/23 23:25:35]

Done.

+}
+
+CopyOnWriteBuffer::CopyOnWriteBuffer(size_t size) {
+  if (size > 0) {
+    buffer_ = new RefCountedObject<Buffer>(size);
+  }
+}
+
+CopyOnWriteBuffer::CopyOnWriteBuffer(size_t size, size_t capacity) {
+  if (size > 0 || capacity > 0) {
+    buffer_ = new RefCountedObject<Buffer>(size, capacity);
+  }
+}

[kwiberg-webrtc, 2016/02/20 06:43:32]

If you wanted to, you could use ?: to set these in the initializers instead of
in the constructor body.

[joachim, 2016/02/23 23:25:35]

Done.

+
+CopyOnWriteBuffer::~CopyOnWriteBuffer() = default;
+
+}  // namespace rtc