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