Add CopyOnWriteBuffer class
This CL introduces a new class CopyOnWriteBuffer that holds data in a
refcounted Buffer which is shared between copied CopyOnWriteBuffer to avoid
unnecessary allocations / memory copies.
BUG=webrtc:5155
Review URL: https://codereview.webrtc.org/1697743003
Cr-Commit-Position: refs/heads/master@{#11767}
diff --git a/webrtc/base/copyonwritebuffer.h b/webrtc/base/copyonwritebuffer.h
new file mode 100644
index 0000000..17f2710
--- /dev/null
+++ b/webrtc/base/copyonwritebuffer.h
@@ -0,0 +1,256 @@
+/*
+ * 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.
+ */
+
+#ifndef WEBRTC_BASE_COPYONWRITEBUFFER_H_
+#define WEBRTC_BASE_COPYONWRITEBUFFER_H_
+
+#include <algorithm>
+#include <utility>
+
+#include "webrtc/base/buffer.h"
+#include "webrtc/base/checks.h"
+#include "webrtc/base/refcount.h"
+#include "webrtc/base/scoped_ref_ptr.h"
+
+namespace rtc {
+
+class CopyOnWriteBuffer {
+ public:
+ // An empty buffer.
+ CopyOnWriteBuffer();
+ // Copy size and contents of an existing buffer.
+ CopyOnWriteBuffer(const CopyOnWriteBuffer& buf);
+ // Move contents from an existing buffer.
+ CopyOnWriteBuffer(CopyOnWriteBuffer&& buf);
+
+ // Construct a buffer with the specified number of uninitialized bytes.
+ explicit CopyOnWriteBuffer(size_t size);
+ CopyOnWriteBuffer(size_t size, size_t capacity);
+
+ // Construct a buffer and copy the specified number of bytes into it. The
+ // source array may be (const) uint8_t*, int8_t*, or char*.
+ template <typename T, typename internal::ByteType<T>::t = 0>
+ CopyOnWriteBuffer(const T* data, size_t size)
+ : CopyOnWriteBuffer(data, size, size) {}
+ template <typename T, typename internal::ByteType<T>::t = 0>
+ CopyOnWriteBuffer(const T* data, size_t size, size_t capacity)
+ : CopyOnWriteBuffer(size, capacity) {
+ std::memcpy(buffer_->data(), data, size);
+ }
+
+ // Construct a buffer from the contents of an array.
+ template <typename T, size_t N, typename internal::ByteType<T>::t = 0>
+ CopyOnWriteBuffer(const T(&array)[N]) // NOLINT: runtime/explicit
+ : CopyOnWriteBuffer(array, N) {}
+
+ ~CopyOnWriteBuffer();
+
+ // Get a pointer to the data. Just .data() will give you a (const) uint8_t*,
+ // but you may also use .data<int8_t>() and .data<char>().
+ template <typename T = uint8_t, typename internal::ByteType<T>::t = 0>
+ const T* data() const {
+ return cdata<T>();
+ }
+
+ // Get writable pointer to the data. This will create a copy of the underlying
+ // data if it is shared with other buffers.
+ template <typename T = uint8_t, typename internal::ByteType<T>::t = 0>
+ T* data() {
+ RTC_DCHECK(IsConsistent());
+ if (!buffer_) {
+ return nullptr;
+ }
+ CloneDataIfReferenced(buffer_->capacity());
+ return buffer_->data<T>();
+ }
+
+ // Get const pointer to the data. This will not create a copy of the
+ // underlying data if it is shared with other buffers.
+ template <typename T = uint8_t, typename internal::ByteType<T>::t = 0>
+ T* cdata() const {
+ RTC_DCHECK(IsConsistent());
+ if (!buffer_) {
+ return nullptr;
+ }
+ return buffer_->data<T>();
+ }
+
+ size_t size() const {
+ RTC_DCHECK(IsConsistent());
+ return buffer_ ? buffer_->size() : 0;
+ }
+
+ size_t capacity() const {
+ RTC_DCHECK(IsConsistent());
+ return buffer_ ? buffer_->capacity() : 0;
+ }
+
+ CopyOnWriteBuffer& operator=(const CopyOnWriteBuffer& buf) {
+ RTC_DCHECK(IsConsistent());
+ RTC_DCHECK(buf.IsConsistent());
+ if (&buf != this) {
+ buffer_ = buf.buffer_;
+ }
+ return *this;
+ }
+
+ CopyOnWriteBuffer& operator=(CopyOnWriteBuffer&& buf) {
+ RTC_DCHECK(IsConsistent());
+ RTC_DCHECK(buf.IsConsistent());
+ // TODO(jbauch): use std::move once scoped_refptr supports it (issue 5556)
+ buffer_.swap(buf.buffer_);
+ buf.buffer_ = nullptr;
+ return *this;
+ }
+
+ bool operator==(const CopyOnWriteBuffer& buf) const {
+ // Must either use the same buffer internally or have the same contents.
+ RTC_DCHECK(IsConsistent());
+ RTC_DCHECK(buf.IsConsistent());
+ return buffer_.get() == buf.buffer_.get() ||
+ (buffer_.get() && buf.buffer_.get() &&
+ *buffer_.get() == *buf.buffer_.get());
+ }
+
+ bool operator!=(const CopyOnWriteBuffer& buf) const {
+ return !(*this == buf);
+ }
+
+ // Replace the contents of the buffer. Accepts the same types as the
+ // constructors.
+ template <typename T, typename internal::ByteType<T>::t = 0>
+ void SetData(const T* data, size_t size) {
+ RTC_DCHECK(IsConsistent());
+ if (!buffer_ || !buffer_->HasOneRef()) {
+ buffer_ = new RefCountedObject<Buffer>(data, size, size);
+ } else {
+ buffer_->SetData(data, size);
+ }
+ RTC_DCHECK(IsConsistent());
+ }
+
+ template <typename T, size_t N, typename internal::ByteType<T>::t = 0>
+ void SetData(const T(&array)[N]) {
+ SetData(array, N);
+ }
+
+ void SetData(const CopyOnWriteBuffer& buf) {
+ RTC_DCHECK(IsConsistent());
+ RTC_DCHECK(buf.IsConsistent());
+ if (&buf != this) {
+ buffer_ = buf.buffer_;
+ }
+ }
+
+ // Append data to the buffer. Accepts the same types as the constructors.
+ template <typename T, typename internal::ByteType<T>::t = 0>
+ void AppendData(const T* data, size_t size) {
+ RTC_DCHECK(IsConsistent());
+ if (!buffer_) {
+ buffer_ = new RefCountedObject<Buffer>(data, size);
+ RTC_DCHECK(IsConsistent());
+ return;
+ }
+
+ CloneDataIfReferenced(std::max(buffer_->capacity(),
+ buffer_->size() + size));
+ buffer_->AppendData(data, size);
+ RTC_DCHECK(IsConsistent());
+ }
+
+ template <typename T, size_t N, typename internal::ByteType<T>::t = 0>
+ void AppendData(const T(&array)[N]) {
+ AppendData(array, N);
+ }
+
+ void AppendData(const CopyOnWriteBuffer& buf) {
+ AppendData(buf.data(), buf.size());
+ }
+
+ // Sets the size of the buffer. If the new size is smaller than the old, the
+ // buffer contents will be kept but truncated; if the new size is greater,
+ // the existing contents will be kept and the new space will be
+ // uninitialized.
+ void SetSize(size_t size) {
+ RTC_DCHECK(IsConsistent());
+ if (!buffer_) {
+ if (size > 0) {
+ buffer_ = new RefCountedObject<Buffer>(size);
+ }
+ RTC_DCHECK(IsConsistent());
+ return;
+ }
+
+ CloneDataIfReferenced(std::max(buffer_->capacity(), size));
+ buffer_->SetSize(size);
+ RTC_DCHECK(IsConsistent());
+ }
+
+ // Ensure that the buffer size can be increased to at least capacity without
+ // further reallocation. (Of course, this operation might need to reallocate
+ // the buffer.)
+ void EnsureCapacity(size_t capacity) {
+ RTC_DCHECK(IsConsistent());
+ if (!buffer_) {
+ if (capacity > 0) {
+ buffer_ = new RefCountedObject<Buffer>(0, capacity);
+ }
+ RTC_DCHECK(IsConsistent());
+ return;
+ } else if (capacity <= buffer_->capacity()) {
+ return;
+ }
+
+ CloneDataIfReferenced(std::max(buffer_->capacity(), capacity));
+ buffer_->EnsureCapacity(capacity);
+ RTC_DCHECK(IsConsistent());
+ }
+
+ // Resets the buffer to zero size and capacity.
+ void Clear() {
+ RTC_DCHECK(IsConsistent());
+ if (!buffer_ || !buffer_->HasOneRef()) {
+ buffer_ = nullptr;
+ } else {
+ buffer_->Clear();
+ }
+ RTC_DCHECK(IsConsistent());
+ }
+
+ // Swaps two buffers.
+ friend void swap(CopyOnWriteBuffer& a, CopyOnWriteBuffer& b) {
+ std::swap(a.buffer_, b.buffer_);
+ }
+
+ private:
+ // Create a copy of the underlying data if it is referenced from other Buffer
+ // objects.
+ void CloneDataIfReferenced(size_t new_capacity) {
+ if (buffer_->HasOneRef()) {
+ return;
+ }
+
+ buffer_ = new RefCountedObject<Buffer>(buffer_->data(), buffer_->size(),
+ new_capacity);
+ RTC_DCHECK(IsConsistent());
+ }
+
+ // Pre- and postcondition of all methods.
+ bool IsConsistent() const {
+ return (!buffer_ || buffer_->capacity() > 0);
+ }
+
+ // buffer_ is either null, or points to an rtc::Buffer with capacity > 0.
+ scoped_refptr<RefCountedObject<Buffer>> buffer_;
+};
+
+} // namespace rtc
+
+#endif // WEBRTC_BASE_COPYONWRITEBUFFER_H_