Introduce shared_memory_support media target for PPAPI

media/audio/shared_memory_util.cc

+// Copyright (c) 2012 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 "media/audio/shared_memory_util.h"
+
+#include "base/atomicops.h"
+#include "base/logging.h"
+
+using base::subtle::Atomic32;
+
+static const uint32 kUnknownDataSize = static_cast<uint32>(-1);
+
+namespace media {
+
+// When transferring data in the shared memory, first word is size of data
+// in bytes. Actual data starts immediately after it.

[nfullagar, 2012/08/17 00:52:07]

Comment above: ...last word is size of data in bytes.

[DaleCurtis, 2012/08/17 02:27:45]

Done.

+
+uint32 TotalSharedMemorySizeInBytes(uint32 packet_size) {
+  // Need to reserve extra 4 bytes for size of data.
+  return packet_size + sizeof(Atomic32);
+}
+
+uint32 PacketSizeSizeInBytes(uint32 shared_memory_created_size) {
+  return shared_memory_created_size - sizeof(Atomic32);
+}
+
+uint32 GetActualDataSizeInBytes(base::SharedMemory* shared_memory,
+                                uint32 shared_memory_size) {
+  char* ptr = static_cast<char*>(shared_memory->memory()) + shared_memory_size;
+  DCHECK_EQ(0u, reinterpret_cast<size_t>(ptr) & 3);
+
+  // Actual data size stored at the end of the buffer.
+  uint32 actual_data_size =
+      base::subtle::Acquire_Load(reinterpret_cast<volatile Atomic32*>(ptr));
+  return std::min(actual_data_size, shared_memory_size);
+}
+
+void SetActualDataSizeInBytes(void* shared_memory_ptr,
+                              uint32 shared_memory_size,
+                              uint32 actual_data_size) {
+  char* ptr = static_cast<char*>(shared_memory_ptr) + shared_memory_size;
+  DCHECK_EQ(0u, reinterpret_cast<size_t>(ptr) & 3);
+
+  // Set actual data size at the end of the buffer.
+  base::subtle::Release_Store(reinterpret_cast<volatile Atomic32*>(ptr),
+                              actual_data_size);
+}
+
+void SetActualDataSizeInBytes(base::SharedMemory* shared_memory,
+                              uint32 shared_memory_size,
+                              uint32 actual_data_size) {
+  SetActualDataSizeInBytes(shared_memory->memory(),
+                           shared_memory_size, actual_data_size);
+}
+
+void SetUnknownDataSize(base::SharedMemory* shared_memory,
+                        uint32 shared_memory_size) {
+  SetActualDataSizeInBytes(shared_memory, shared_memory_size, kUnknownDataSize);
+}
+
+bool IsUnknownDataSize(base::SharedMemory* shared_memory,
+                       uint32 shared_memory_size) {
+  char* ptr = static_cast<char*>(shared_memory->memory()) + shared_memory_size;
+  DCHECK_EQ(0u, reinterpret_cast<size_t>(ptr) & 3);
+
+  // Actual data size stored at the end of the buffer.
+  uint32 actual_data_size =
+      base::subtle::Acquire_Load(reinterpret_cast<volatile Atomic32*>(ptr));
+  return actual_data_size == kUnknownDataSize;
+}
+
+}  // namespace media