media/audio/shared_memory_util.cc

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "media/audio/shared_memory_util.h"
   6
   7 #include <algorithm>
   8
   9 #include "base/atomicops.h"
  10 #include "base/logging.h"
  11
  12 using base::subtle::Atomic32;
  13
  14 static const uint32 kUnknownDataSize = static_cast<uint32>(-1);
  15
  16 namespace media {
  17
  18 uint32 TotalSharedMemorySizeInBytes(uint32 packet_size) {
  19   // Need to reserve extra 4 bytes for size of data.
  20   return packet_size + sizeof(Atomic32);
  21 }
  22
  23 uint32 PacketSizeInBytes(uint32 shared_memory_created_size) {
  24   return shared_memory_created_size - sizeof(Atomic32);
  25 }
  26
  27 uint32 GetActualDataSizeInBytes(base::SharedMemory* shared_memory,
  28                                 uint32 packet_size) {
  29   char* ptr = static_cast<char*>(shared_memory->memory()) + packet_size;
  30   DCHECK_EQ(0u, reinterpret_cast<size_t>(ptr) & 3);
  31
  32   // Actual data size stored at the end of the buffer.
  33   uint32 actual_data_size =
  34       base::subtle::Acquire_Load(reinterpret_cast<volatile Atomic32*>(ptr));
  35   return std::min(actual_data_size, packet_size);
  36 }
  37
  38 void SetActualDataSizeInBytes(void* shared_memory_ptr,
  39                               uint32 packet_size,
  40                               uint32 actual_data_size) {
  41   char* ptr = static_cast<char*>(shared_memory_ptr) + packet_size;
  42   DCHECK_EQ(0u, reinterpret_cast<size_t>(ptr) & 3);
  43
  44   // Set actual data size at the end of the buffer.
  45   base::subtle::Release_Store(reinterpret_cast<volatile Atomic32*>(ptr),
  46                               actual_data_size);
  47 }
  48
  49 void SetActualDataSizeInBytes(base::SharedMemory* shared_memory,
  50                               uint32 packet_size,
  51                               uint32 actual_data_size) {
  52   SetActualDataSizeInBytes(shared_memory->memory(),
  53                            packet_size, actual_data_size);
  54 }
  55
  56 void SetUnknownDataSize(base::SharedMemory* shared_memory,
  57                         uint32 packet_size) {
  58   SetActualDataSizeInBytes(shared_memory, packet_size, kUnknownDataSize);
  59 }
  60
  61 bool IsUnknownDataSize(base::SharedMemory* shared_memory,
  62                        uint32 packet_size) {
  63   char* ptr = static_cast<char*>(shared_memory->memory()) + packet_size;
  64   DCHECK_EQ(0u, reinterpret_cast<size_t>(ptr) & 3);
  65
  66   // Actual data size stored at the end of the buffer.
  67   uint32 actual_data_size =
  68       base::subtle::Acquire_Load(reinterpret_cast<volatile Atomic32*>(ptr));
  69   return actual_data_size == kUnknownDataSize;
  70 }
  71
  72 }  // namespace media