Add CopyOnWriteBuffer class

webrtc/base/buffer.cc

 /*
  *  Copyright 2015 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 <utility>
+
+#include "webrtc/base/checks.h"
 #include "webrtc/base/buffer.h"
 
-#include <cassert>
-#include <utility>
-
 namespace rtc {
 
-Buffer::Buffer() : size_(0), capacity_(0), data_(nullptr) {
-  assert(IsConsistent());
+namespace internal {
+
+BufferData::BufferData()
+    : size_(0),
+      capacity_(0),
+      data_(nullptr) {
+  RTC_DCHECK(IsConsistent());
 }
 
-Buffer::Buffer(const Buffer& buf) : Buffer(buf.data(), buf.size()) {
+BufferData::BufferData(const BufferData& data)
+    : size_(data.size_),
+      capacity_(data.capacity_),
+      data_(new uint8_t[capacity_]) {
+  RTC_DCHECK(IsConsistent());
+  if (data.size_) {
+    std::memcpy(data_.get(), data.data_.get(), data.size_);
+  }
 }
 
-Buffer::Buffer(Buffer&& buf)
-    : size_(buf.size()),
-      capacity_(buf.capacity()),
-      data_(std::move(buf.data_)) {
-  assert(IsConsistent());
+BufferData::BufferData(size_t size) : BufferData(size, size) {
+}
+
+BufferData::BufferData(size_t size, size_t capacity)
+    : size_(size),
+      capacity_(std::max(size, capacity)),
+      data_(new uint8_t[capacity_]) {
+  RTC_DCHECK(IsConsistent());
+}
+
+BufferData::BufferData(const void* data, size_t size)
+    : BufferData(data, size, size) {
+}
+
+BufferData::BufferData(const void* data, size_t size, size_t capacity)
+    : BufferData(size, capacity) {
+  std::memcpy(data_.get(), data, size);
+}
+
+}  // namespace internal
+
+
+Buffer::Buffer() : data_(new internal::BufferData()) {
+}

[kwiberg-webrtc, 2016/02/14 14:43:45]

Hmm. With this change, you no longer have the property that an empty buffer
makes no allocations.

[joachim, 2016/02/14 17:10:16]

Changed to only allocate if necessary.

+
+Buffer::Buffer(const Buffer& buf) : data_(buf.data_) {
+}
+
+Buffer::Buffer(Buffer&& buf) : data_(std::move(buf.data_)) {
   buf.OnMovedFrom();
 }
 
 Buffer::Buffer(size_t size) : Buffer(size, size) {
 }
 
 Buffer::Buffer(size_t size, size_t capacity)
-    : size_(size),
-      capacity_(std::max(size, capacity)),
-      data_(new uint8_t[capacity_]) {
-  assert(IsConsistent());
+    : data_(new internal::BufferData(size, capacity)) {
+  RTC_DCHECK(IsConsistent());
 }
 
-// Note: The destructor works even if the buffer has been moved from.
-Buffer::~Buffer() = default;
+Buffer::~Buffer() {
+}

[kwiberg-webrtc, 2016/02/14 14:43:45]

Why not =default? It's one line shorter...

[joachim, 2016/02/14 17:10:16]

Right, that was a leftover of some earlier patch set. Reverted to original dtor.

 
 };  // namespace rtc