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,
+    int shared_memory_segment_count)
+    : shared_memory_(shared_memory),
+      shared_memory_segment_count_(shared_memory_segment_count),
+      current_segment_id_(0) {
+  DCHECK_LT(0, shared_memory_segment_count);

[DaleCurtis, 2013/03/07 02:04:37]

No yoda checks please; it's against style.
 
DCHECK_GE(shared_memory_segment_count, 0)

[wjia(left Chromium), 2013/03/10 18:19:49]

During my readability code review, I was told to put expected value as first
argument of CHECK. Yuri also mentioned this in his comment
(https://codereview.chromium.org/12379071/diff/38001/content/browser/renderer_...).

I'd like to have clarification.

[DaleCurtis, 2013/03/11 20:00:47]

http://dev.chromium.org/developers/coding-style specifically: "Prefer (foo == 0)
to (0 == foo)."  Also I had Yuri change all his in a recent CL too :)

[wjia(left Chromium), 2013/03/11 20:34:27]

Done.

+  DCHECK_EQ(0u, shared_memory->created_size() % shared_memory_segment_count);
+  shared_memory_segment_size_ =
+      shared_memory->created_size() / shared_memory_segment_count;
 }
 
 AudioInputSyncWriter::~AudioInputSyncWriter() {}
@@ -22,14 +30,19 @@
   socket_->Send(&bytes, sizeof(bytes));
 }
 
-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());

[DaleCurtis, 2013/03/07 02:04:37]

Should be able static_cast a void* ?

[wjia(left Chromium), 2013/03/10 18:19:49]

Done.

+  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);
 
+  if (++current_segment_id_ >= shared_memory_segment_count_)

[DaleCurtis, 2013/03/07 02:04:37]

current_segment_id_ = (current_segment_id_ + 1) % shared_memory_segement_count_;

to avoid the conditional.

[wjia(left Chromium), 2013/03/10 18:19:49]

I think it's more clearer and less expensive to use if condition. 

[DaleCurtis, 2013/03/11 20:00:47]

Just a nit, so fine with me either way.  I assume a branch is more expensive
than a modulus operation, but feel free to paint your bike shed whatever color
you want :)

+    current_segment_id_ = 0;
+
   return size;
 }