Workaround for race condition between audio host and renderer

media/audio/audio_util.cc

Index: media/audio/audio_util.cc
===================================================================
--- media/audio/audio_util.cc	(revision 100908)
+++ media/audio/audio_util.cc	(working copy)
@@ -21,6 +21,8 @@
 
 using base::subtle::Atomic32;
 
+const uint32 kUnknownDataSize = static_cast<uint32>(-1);
+
 namespace media {
 
 // TODO(fbarchard): Convert to intrinsics for better efficiency.
@@ -257,7 +259,7 @@
   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);
@@ -269,9 +271,25 @@
   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