IPC to pass media data using a lock free circular fifo.

chromecast/media/cma/ipc/media_message.cc

+// Copyright 2014 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 "chromecast/media/cma/ipc/media_message.h"
+
+#include <limits>
+
+#include "base/basictypes.h"
+#include "base/logging.h"
+#include "chromecast/media/cma/ipc/media_memory_chunk.h"
+
+namespace chromecast {
+namespace media {
+
+// static
+scoped_ptr<MediaMessage> MediaMessage::CreateDummyMessage(
+    uint32 type) {
+  return scoped_ptr<MediaMessage>(
+      new MediaMessage(type, std::numeric_limits<size_t>::max()));
+}
+
+// static
+scoped_ptr<MediaMessage> MediaMessage::CreateMessage(
+    uint32 type,
+    const MemoryAllocatorCB& memory_allocator,
+    size_t msg_content_capacity) {
+  size_t msg_size = minimum_msg_size() + msg_content_capacity;
+
+  // Make the message size a multiple of the alignment
+  // so that if we have proper alignment for array of messages.
+  size_t end_alignment = msg_size % ALIGNOF(SerializedMsg);
+  if (end_alignment != 0)
+    msg_size += ALIGNOF(SerializedMsg) - end_alignment;
+
+  scoped_ptr<MediaMemoryChunk> memory(memory_allocator.Run(msg_size));
+  if (!memory)
+    return scoped_ptr<MediaMessage>();
+
+  return scoped_ptr<MediaMessage>(new MediaMessage(type, memory.Pass()));
+}
+
+// static
+scoped_ptr<MediaMessage> MediaMessage::CreateMessage(
+    uint32 type,
+    scoped_ptr<MediaMemoryChunk> memory) {
+  return scoped_ptr<MediaMessage>(new MediaMessage(type, memory.Pass()));
+}
+
+// static
+scoped_ptr<MediaMessage> MediaMessage::MapMessage(
+    scoped_ptr<MediaMemoryChunk> memory) {
+  return scoped_ptr<MediaMessage>(new MediaMessage(memory.Pass()));
+}
+
+MediaMessage::MediaMessage(uint32 type, size_t msg_size)
+  : is_dummy_msg_(true),
+    cached_header_(&cached_msg_.header),
+    msg_(&cached_msg_),
+    msg_read_only_(&cached_msg_),
+    rd_offset_(0) {
+  cached_header_->size = msg_size;
+  cached_header_->type = type;
+  cached_header_->content_size = 0;
+}
+
+MediaMessage::MediaMessage(uint32 type, scoped_ptr<MediaMemoryChunk> memory)
+  : is_dummy_msg_(false),
+    cached_header_(&cached_msg_.header),
+    msg_(static_cast<SerializedMsg*>(memory->data())),
+    msg_read_only_(msg_),
+    mem_(memory.Pass()),
+    rd_offset_(0) {
+  CHECK(mem_->valid());
+  CHECK_GE(mem_->size(), minimum_msg_size());
+
+  // Check memory alignment:
+  // needed to cast properly |msg_dst| to a SerializedMsg.
+  CHECK_EQ(
+      reinterpret_cast<uintptr_t>(mem_->data()) % ALIGNOF(SerializedMsg), 0u);
+
+  // Make sure that |mem_->data()| + |mem_->size()| is also aligned correctly.
+  // This is needed if we append a second serialized message next to this one.
+  // The second serialized message must be aligned correctly.
+  // It is similar to what a compiler is doing for arrays of structures.
+  CHECK_EQ(mem_->size() % ALIGNOF(SerializedMsg), 0u);
+
+  cached_header_->size = mem_->size();
+  cached_header_->type = type;
+  cached_header_->content_size = 0;
+  msg_->header = *cached_header_;
+}
+
+MediaMessage::MediaMessage(scoped_ptr<MediaMemoryChunk> memory)
+  : is_dummy_msg_(false),
+    cached_header_(&cached_msg_.header),
+    msg_(NULL),
+    msg_read_only_(static_cast<SerializedMsg*>(memory->data())),
+    mem_(memory.Pass()),
+    rd_offset_(0) {
+  CHECK(mem_->valid());
+
+  // Check memory alignment.
+  CHECK_EQ(
+      reinterpret_cast<uintptr_t>(mem_->data()) % ALIGNOF(SerializedMsg), 0u);
+
+  // Cache the message header which cannot be modified while reading.
+  CHECK_GE(mem_->size(), minimum_msg_size());
+  *cached_header_ = msg_read_only_->header;
+  CHECK_GE(cached_header_->size, minimum_msg_size());
+
+  // Make sure if we have 2 consecutive serialized messages in memory,
+  // the 2nd message is also aligned correctly.
+  CHECK_EQ(cached_header_->size % ALIGNOF(SerializedMsg), 0u);
+
+  size_t max_content_size = cached_header_->size - minimum_msg_size();
+  CHECK_LE(cached_header_->content_size, max_content_size);
+}
+
+MediaMessage::~MediaMessage() {
+}
+
+bool MediaMessage::IsSerializedMsgAvailable() const {
+  return !is_dummy_msg_ && mem_->valid();
+}
+
+bool MediaMessage::WriteBuffer(const void* src, size_t size) {
+  // No message to write into.
+  if (!msg_)
+    return false;
+
+  // The underlying memory was invalidated.
+  if (!is_dummy_msg_ && !mem_->valid())
+    return false;
+
+  size_t max_content_size = cached_header_->size - minimum_msg_size();
+  if (cached_header_->content_size + size > max_content_size) {
+    cached_header_->content_size = max_content_size;
+    msg_->header.content_size = cached_header_->content_size;
+    return false;
+  }
+
+  // Write the message only for non-dummy messages.
+  if (!is_dummy_msg_) {
+    uint8* wr_ptr = &msg_->content + cached_header_->content_size;
+    memcpy(wr_ptr, src, size);
+  }
+
+  cached_header_->content_size += size;
+  msg_->header.content_size = cached_header_->content_size;
+  return true;
+}
+
+bool MediaMessage::ReadBuffer(void* dst, size_t size) {
+  // No read possible for a dummy message.
+  if (is_dummy_msg_)
+    return false;
+
+  // The underlying memory was invalidated.
+  if (!mem_->valid())
+    return false;
+
+  if (rd_offset_ + size > cached_header_->content_size) {
+    rd_offset_ = cached_header_->content_size;
+    return false;
+  }
+
+  const uint8* rd_ptr = &msg_read_only_->content + rd_offset_;
+  memcpy(dst, rd_ptr, size);
+  rd_offset_ += size;
+  return true;
+}
+
+void* MediaMessage::GetWritableBuffer(size_t size) {
+  // No read possible for a dummy message.
+  if (is_dummy_msg_)
+    return NULL;
+
+  // The underlying memory was invalidated.
+  if (!mem_->valid())
+    return NULL;
+
+  if (rd_offset_ + size > cached_header_->content_size) {
+    rd_offset_ = cached_header_->content_size;
+    return NULL;
+  }
+
+  uint8* rd_ptr = &msg_read_only_->content + rd_offset_;
+  rd_offset_ += size;
+  return rd_ptr;
+}
+
+const void* MediaMessage::GetBuffer(size_t size) {
+  return GetWritableBuffer(size);
+}
+
+}  // namespace media
+}  // namespace chromecast