Use multiple shared memory buffers cyclically for audio capture.

content/browser/renderer_host/media/audio_input_sync_writer.cc

Index: content/browser/renderer_host/media/audio_input_sync_writer.cc
===================================================================
--- content/browser/renderer_host/media/audio_input_sync_writer.cc	(revision 186364)
+++ content/browser/renderer_host/media/audio_input_sync_writer.cc	(working copy)
@@ -11,8 +11,16 @@
 
 namespace content {
 
-AudioInputSyncWriter::AudioInputSyncWriter(base::SharedMemory* shared_memory)
-    : shared_memory_(shared_memory) {
+AudioInputSyncWriter::AudioInputSyncWriter(
+    base::SharedMemory* shared_memory,
+    uint32 shared_memory_segment_count)
+    : shared_memory_(shared_memory),
+      shared_memory_segment_count_(shared_memory_segment_count),
+      current_segment_id_(0) {
+  DCHECK(shared_memory_segment_count);

[miu, 2013/03/06 18:06:41]

Should be DCHECK_LT(0, shared_memory_segment_count_);

[wjia(left Chromium), 2013/03/06 22:12:41]

Done.

+  DCHECK_EQ(shared_memory->created_size() % shared_memory_segment_count, 0u);
+  shared_memory_segment_size_ =
+      shared_memory->created_size() / shared_memory_segment_count;
 }
 
 AudioInputSyncWriter::~AudioInputSyncWriter() {}
@@ -20,12 +28,20 @@
 // TODO(henrika): Combine into one method (including Write).
 void AudioInputSyncWriter::UpdateRecordedBytes(uint32 bytes) {
   socket_->Send(&bytes, sizeof(bytes));
+  // The shared memory has multiple equal lengthed segments used to transfer
+  // recorded data. Each time, one segment is used. Both data size and segment
+  // id need to be sent to the receiver.
+  socket_->Send(&current_segment_id_, sizeof(current_segment_id_));

[miu, 2013/03/06 18:06:41]

Agree with Dale: That you don't need to send this if the socket is a reliable
data channel, as this is data that both sides already have.

[wjia(left Chromium), 2013/03/06 22:12:41]

Done. I still think such constraint shouldn't be put in the code.

+  if (++current_segment_id_ >= shared_memory_segment_count_)
+    current_segment_id_ = 0;
 }
 
-uint32 AudioInputSyncWriter::Write(const void* data, uint32 size,
-                                   double volume) {
+uint32 AudioInputSyncWriter::Write(
+    const void* data, uint32 size, double volume) {
+  uint8* ptr = reinterpret_cast<uint8*>(shared_memory_->memory());
+  ptr += current_segment_id_ * shared_memory_segment_size_;
   media::AudioInputBuffer* buffer =
-      reinterpret_cast<media::AudioInputBuffer*>(shared_memory_->memory());
+      reinterpret_cast<media::AudioInputBuffer*>(ptr);
   buffer->params.volume = volume;
   buffer->params.size = size;
   memcpy(buffer->audio, data, size);