Pad time to next audio data write to compensate for nanosleep inaccuracy on linux.

media/audio/linux/alsa_output.cc

 // Copyright (c) 2009 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.
 //
 // THREAD SAFETY
 //
 // The AlsaPcmOutputStream object's internal state is accessed by two threads:
 //
 //   client thread - creates the object and calls the public APIs.
 //   message loop thread - executes all the internal tasks including querying
@@ skipping 70 matching lines @@
 #include "base/stl_util-inl.h"
 #include "base/time.h"
 #include "media/audio/audio_util.h"
 #include "media/audio/linux/alsa_wrapper.h"
 #include "media/audio/linux/audio_manager_linux.h"
 
 // Amount of time to wait if we've exhausted the data source.  This is to avoid
 // busy looping.
 static const int kNoDataSleepMilliseconds = 10;
 
+// According to the linux nanosleep manpage, nanosleep on linux can miss the
+// deadline by up to 10ms because the kernel timeslice is 10ms.  Give a 2x
+// buffer to compensate for the timeslice, and any additional slowdowns.
+static const int kSleepErrorMilliseconds = 20;
+
 // Set to 0 during debugging if you want error messages due to underrun
 // events or other recoverable errors.
 #if defined(NDEBUG)
 static const int kPcmRecoverIsSilent = 1;
 #else
 static const int kPcmRecoverIsSilent = 0;
 #endif
 
 const char AlsaPcmOutputStream::kDefaultDevice[] = "default";
 
@@ skipping 392 matching lines @@
   }
 
   // Calculate when we should have enough buffer for another packet of data.
   int frames_leftover = FramesInPacket(*current_packet, bytes_per_frame_);
   int frames_needed =
       frames_leftover > 0 ? frames_leftover : frames_per_packet_;
   int frames_until_empty_enough = frames_needed - GetAvailableFrames();
   int next_fill_time_ms =
       FramesToMillis(frames_until_empty_enough, sample_rate_);
 
+  // Adjust for timer resolution issues.
+  if (next_fill_time_ms > kSleepErrorMilliseconds) {
+    next_fill_time_ms -= kSleepErrorMilliseconds;
+  }
+
   // Avoid busy looping if the data source is exhausted.
   if (current_packet->size == 0) {
     next_fill_time_ms = std::max(next_fill_time_ms, kNoDataSleepMilliseconds);
   }
 
   // Only schedule more reads/writes if we are still in the playing state.
   if (shared_data_.state() == kIsPlaying) {
     if (next_fill_time_ms <= 0) {
       message_loop_->PostTask(
           FROM_HERE,
@@ skipping 161 matching lines @@
 }
 
 // Changes the AudioSourceCallback to proxy calls to.  Pass in NULL to
 // release ownership of the currently registered callback.
 void AlsaPcmOutputStream::SharedData::set_source_callback(
     AudioSourceCallback* callback) {
   DCHECK_EQ(MessageLoop::current(), state_transition_loop_);
   AutoLock l(lock_);
   source_callback_ = callback;
 }