Rewriting WebRTC output level tests to be more reliable under load.

content/test/data/media/webrtc_test_audio.js

 // Copyright 2013 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.
 
 // Audio test utilities.
 
 // GetStats reports audio output energy in the [0, 32768] range.
 var MAX_AUDIO_OUTPUT_ENERGY = 32768;
 
 // Queries WebRTC stats on |peerConnection| to find out whether audio is playing
 // on the connection. Note this does not necessarily mean the audio is actually
 // playing out (for instance if there's a bug in the WebRTC web media player).
 // If |beLenient| is true, we assume we're on a slow and unreliable bot and that
 // we should do a minimum of checking.
 function ensureAudioPlaying(peerConnection, beLenient) {
   addExpectedEvent();
 
-  // Gather 50 samples per second for 2 seconds.
-  gatherAudioLevelSamples(peerConnection, 100, 50, function(samples) {
+  gatherAudioLevelSamples(peerConnection, 3 * 1000, function(samples) {
     identifyFakeDeviceSignal_(samples, beLenient);
     eventOccured();
   });
 }
 
 // Queries WebRTC stats on |peerConnection| to find out whether audio is muted
 // on the connection.
 function ensureSilence(peerConnection) {
   addExpectedEvent();
   setTimeout(function() {
-    gatherAudioLevelSamples(peerConnection, 100, 50, function(samples) {
+    gatherAudioLevelSamples(peerConnection, 1 * 1000, function(samples) {
       identifySilence_(samples);
       eventOccured();
     });
   }, 500);
 }
 
 // Not sure if this is a bug, but sometimes we get several audio ssrc's where
 // just reports audio level zero. Think of the nonzero level as the more
 // credible one here. http://crbug.com/479147.
 function workAroundSeveralReportsIssue(audioOutputLevels) {
   if (audioOutputLevels.length == 1) {
     return audioOutputLevels[0];
   }
 
   console.log("Hit issue where one report batch returns two or more reports " +
               "with audioReportLevel; got " + audioOutputLevels);
 
   return Math.max(audioOutputLevels[0], audioOutputLevels[1]);
 }
 
-// Gathers |numSamples| samples at |frequency| number of times per second and
-// calls back |callback| with an array with numbers in the [0, 32768] range.
-function gatherAudioLevelSamples(peerConnection, numSamples, frequency,
-                                 callback) {
-  console.log('Gathering ' + numSamples + ' audio samples...');
+// Gathers samples from WebRTC stats as fast as possible for |durationMs|
+// milliseconds and calls back |callback| with an array with numbers in the
+// [0, 32768] range. There are no guarantees for how often we will be able to
+// collect values, but this function deliberately avoids setTimeout calls in
+// order be as insensitive as possible to starvation (particularly when this
+// code runs in parallel with other tests on a heavily loaded bot).
+function gatherAudioLevelSamples(peerConnection, durationMs, callback) {
+  console.log('Gathering audio samples for ' + durationMs + ' milliseconds...');
   var audioLevelSamples = []
 
   // If this times out and never found any audio output levels, the call
   // probably doesn't have an audio stream.
-  var gatherSamples = setInterval(function() {
-    peerConnection.getStats(function(response) {
-      audioOutputLevels = getAudioLevelFromStats_(response);
-      if (audioOutputLevels.length == 0) {
-        // The call probably isn't up yet.
-        return;
-      }
-      var outputLevel = workAroundSeveralReportsIssue(audioOutputLevels);
-      audioLevelSamples.push(outputLevel);
+  var startTime = new Date();
+  var gotStats = function(response) {
+    audioOutputLevels = getAudioLevelFromStats_(response);
+    if (audioOutputLevels.length == 0) {
+      // The call probably isn't up yet.
+      peerConnection.getStats(gotStats);
+      return;
+    }
+    var outputLevel = workAroundSeveralReportsIssue(audioOutputLevels);
+    audioLevelSamples.push(outputLevel);
 
-      if (audioLevelSamples.length == numSamples) {
-        console.log('Gathered all samples.');
-        clearInterval(gatherSamples);
-        callback(audioLevelSamples);
-      }
-    });
-  }, 1000 / frequency);
+    var elapsed = new Date() - startTime;
+    if (elapsed > durationMs) {
+      console.log('Gathered all samples.');
+      callback(audioLevelSamples);
+      return;
+    }
+    peerConnection.getStats(gotStats);
+  }
+  peerConnection.getStats(gotStats);
 }
 
 /**
 * Tries to identify the beep-every-half-second signal generated by the fake
 * audio device in media/video/capture/fake_video_capture_device.cc. Fails the
 * test if we can't see a signal. The samples should have been gathered over at
 * least two seconds since we expect to see at least three "peaks" in there
 * (we should see either 3 or 4 depending on how things line up).
 *
 * If |beLenient| is specified, we assume we're running on a slow device or
 * or under TSAN, and relax the checks quite a bit.
 *
 * @private
 */
 function identifyFakeDeviceSignal_(samples, beLenient) {
   var numPeaks = 0;
   var threshold = MAX_AUDIO_OUTPUT_ENERGY * 0.7;
   if (beLenient)
     threshold = MAX_AUDIO_OUTPUT_ENERGY * 0.6;
   var currentlyOverThreshold = false;
 
   // Detect when we have been been over the threshold and is going back again
-  // (i.e. count peaks). We should see about one peak per second.
+  // (i.e. count peaks). We should see about two peaks per second.
   for (var i = 0; i < samples.length; ++i) {
     if (currentlyOverThreshold && samples[i] < threshold)
       numPeaks++;
     currentlyOverThreshold = samples[i] >= threshold;
   }
 
   console.log('Number of peaks identified: ' + numPeaks);
 
   var expectedPeaks = 2;
   if (beLenient)
@@ skipping 26 matching lines @@
   var reports = response.result();
   var audioOutputLevels = [];
   for (var i = 0; i < reports.length; ++i) {
     var report = reports[i];
     if (report.names().indexOf('audioOutputLevel') != -1) {
       audioOutputLevels.push(report.stat('audioOutputLevel'));
     }
   }
   return audioOutputLevels;
 }