Revert r104043, which causes audio not to play smoothly on Chrome OS.

BUG=chromium-os:21491

Review URL: http://codereview.chromium.org/8329004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@105996 0039d316-1c4b-4281-b951-d872f2087c98

media/audio/linux/alsa_output.cc

@@ -347,8 +347,7 @@ void AlsaPcmOutputStream::OpenTask() {
     if (error < 0) {
       LOG(ERROR) << "Failed to get playback buffer size from ALSA: "
                  << wrapper_->StrError(error);
-      // Buffer size is at least twice of packet size.
-      alsa_buffer_frames_ = 2 * frames_per_packet_;
+      alsa_buffer_frames_ = frames_per_packet_;
     } else {
       alsa_buffer_frames_ = buffer_size;
     }
@@ -598,44 +597,25 @@ void AlsaPcmOutputStream::ScheduleNextWrite(bool source_exhausted) {
     return;
   }
 
-  // Next write is initially scheduled for the moment when half of a packet
-  // has been played out.
-  uint32 minimal_frames_wanted = frames_per_packet_ / 2;
-  uint32 next_fill_time_ms = FramesToMillis(minimal_frames_wanted,
-                                            sample_rate_);
-
-  // Set existing_frames to be minimal_frames_wanted to avoid busy looping
-  // in case alsa_buffer_frames_ is smaller than available_freams.
+  // Next write is scheduled for the moment when half of the buffer is
+  // available.
+  uint32 frames_avail_wanted = alsa_buffer_frames_ / 2;
   uint32 available_frames = GetAvailableFrames();
-  uint32 existing_frames = (alsa_buffer_frames_ >= available_frames) ?
-        (alsa_buffer_frames_ - available_frames) : minimal_frames_wanted;
-
-  // ALSA is full, schedule another write when some buffer is available.
-  // This helps reduce the CPU usage.
-  if (available_frames == 0) {
-    next_fill_time_ms = std::min(next_fill_time_ms, kNoDataSleepMilliseconds);
-    message_loop_->PostDelayedTask(
-          FROM_HERE,
-          base::Bind(&AlsaPcmOutputStream::ScheduleNextWrite,
-                     weak_factory_.GetWeakPtr(), false),
-          next_fill_time_ms);
-    return;
-  }
+  uint32 next_fill_time_ms = 0;
 
-
-  // Re-schedule the next write for the moment when the available buffer is
-  // enough for a packet. Avoid back-to-back writing by setting
-  // kNoDataSleepMilliseconds as the minimal interval.
-  if (available_frames < frames_per_packet_) {
-    next_fill_time_ms = std::max(
-        kNoDataSleepMilliseconds,
-        FramesToMillis(frames_per_packet_ - available_frames,
-                       sample_rate_));
+  // It's possible to have more frames available than what we want, in which
+  // case we'll leave our |next_fill_time_ms| at 0ms.
+  if (available_frames < frames_avail_wanted) {
+    uint32 frames_until_empty_enough = frames_avail_wanted - available_frames;
+    next_fill_time_ms =
+        FramesToMillis(frames_until_empty_enough, sample_rate_);
   }
-  else if (existing_frames < minimal_frames_wanted) {
-    // If less than half of the packet in the buffer, invoke the write callback
-    // immediately to fill more data.
+
+  // Adjust for timer resolution issues.
+  if (next_fill_time_ms < kSleepErrorMilliseconds) {
     next_fill_time_ms = 0;
+  } else {
+    next_fill_time_ms -= kSleepErrorMilliseconds;
   }
 
   // Avoid busy looping if the data source is exhausted.

media/audio/linux/alsa_output_unittest.cc

@@ -436,6 +436,13 @@ TEST_F(AlsaPcmOutputStreamTest, StartStop) {
   EXPECT_CALL(mock_alsa_wrapper_, PcmDelay(kFakeHandle, _))
       .Times(2)
       .WillRepeatedly(DoAll(SetArgumentPointee<1>(0), Return(0)));
+  EXPECT_CALL(mock_callback,
+              OnMoreData(test_stream_.get(), _, kTestPacketSize, _))
+      .Times(2)
+      .WillOnce(Return(kTestPacketSize))
+      .WillOnce(Return(0));
+  EXPECT_CALL(mock_alsa_wrapper_, PcmWritei(kFakeHandle, _, _))
+      .WillOnce(Return(kTestFramesPerPacket));
 
   // Expect scheduling.
   EXPECT_CALL(mock_alsa_wrapper_, PcmAvailUpdate(kFakeHandle))
@@ -446,14 +453,6 @@ TEST_F(AlsaPcmOutputStreamTest, StartStop) {
                                               &MessageLoop::QuitNow),
                                               Return(0)));  // Buffer is full.
 
-  EXPECT_CALL(mock_callback,
-              OnMoreData(test_stream_.get(), _, kTestPacketSize, _))
-      .Times(2)
-      .WillOnce(Return(kTestPacketSize))
-      .WillOnce(Return(0));
-  EXPECT_CALL(mock_alsa_wrapper_, PcmWritei(kFakeHandle, _, _))
-      .WillOnce(Return(kTestFramesPerPacket));
-
   test_stream_->Start(&mock_callback);
   message_loop_.RunAllPending();