Workaround for race condition between audio host and renderer

media/audio/audio_util.cc

 // Copyright (c) 2011 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.
 
 // Software adjust volume of samples, allows each audio stream its own
 // volume without impacting master volume for chrome and other applications.
 
 // Implemented as templates to allow 8, 16 and 32 bit implementations.
 // 8 bit is unsigned and biased by 128.
 
 #include <algorithm>
 
 #include "base/atomicops.h"
 #include "base/basictypes.h"
 #include "base/logging.h"
 #include "base/shared_memory.h"
 #include "media/audio/audio_util.h"
 #if defined(OS_MACOSX)
 #include "media/audio/mac/audio_low_latency_output_mac.h"
 #endif
 
 using base::subtle::Atomic32;
 
+const uint32 kUnknownDataSize = static_cast<uint32>(-1);
+
 namespace media {
 
 // TODO(fbarchard): Convert to intrinsics for better efficiency.
 template<class Fixed>
 static int ScaleChannel(int channel, int volume) {
   return static_cast<int>((static_cast<Fixed>(channel) * volume) >> 16);
 }
 
 template<class Format, class Fixed, int bias>
 static void AdjustVolume(Format* buf_out,
@@ skipping 216 matching lines @@
 
 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 in the beginning of the buffer.
+  // 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(base::SharedMemory* shared_memory,
                               uint32 shared_memory_size,
                               uint32 actual_data_size) {
   char* ptr = static_cast<char*>(shared_memory->memory()) + shared_memory_size;
   DCHECK_EQ(0u, reinterpret_cast<size_t>(ptr) & 3);
 
-  // Set actual data size in the beginning of the buffer.
+  // Set actual data size at the end of the buffer.
   base::subtle::Release_Store(reinterpret_cast<volatile Atomic32*>(ptr),
                               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