Bug 1181073 - Relax setTimeout throttling for background tabs using web audio, r=bkelly

dom/base/nsGlobalWindow.cpp

@@ -307,6 +307,16 @@ static int32_t gMinBackgroundTimeoutValue;
 inline int32_t
 nsGlobalWindow::DOMMinTimeoutValue() const {
   bool isBackground = !mOuterWindow || mOuterWindow->IsBackground();
+  if (isBackground) {
+    // Don't use the background timeout value when there are audio contexts with
+    // active nodes, so that background audio can keep running smoothly.
+    for (const AudioContext* ctx : mAudioContexts) {
+      if (ctx->ActiveNodeCount() > 0) {
+        isBackground = false;
+        break;
+      }
+    }
+  }
   return
     std::max(isBackground ? gMinBackgroundTimeoutValue : gMinTimeoutValue, 0);
 }

dom/media/webaudio/AudioContext.cpp

@@ -696,6 +696,12 @@ AudioContext::MaxChannelCount() const
   return mIsOffline ? mNumberOfChannels : CubebUtils::MaxNumberOfChannels();
 }
 
+uint32_t
+AudioContext::ActiveNodeCount() const
+{
+  return mActiveNodes.Count();
+}
+
 MediaStreamGraph*
 AudioContext::Graph() const
 {

dom/media/webaudio/AudioContext.h

@@ -300,6 +300,8 @@ public:
 
   uint32_t MaxChannelCount() const;
 
+  uint32_t ActiveNodeCount() const;
+
   void Mute() const;
   void Unmute() const;
 

dom/media/webaudio/moz.build

@@ -16,6 +16,10 @@ MOCHITEST_MANIFESTS += [
     'test/mochitest.ini',
 ]
 
+BROWSER_CHROME_MANIFESTS += [
+    'test/browser.ini',
+]
+
 TEST_HARNESS_FILES.testing.mochitest.tests.dom.media.webaudio.test.blink += [
     'test/blink/audio-testing.js',
     'test/blink/convolution-testing.js',

dom/media/webaudio/test/browser.ini

@@ -0,0 +1 @@
+[browser_bug1181073.js]

dom/media/webaudio/test/browser_bug1181073.js

@@ -0,0 +1,65 @@
+add_task(function*() {
+  // Make the min_background_timeout_value very high to avoid problems on slow machines
+  yield new Promise(resolve => SpecialPowers.pushPrefEnv({
+    'set': [['dom.min_background_timeout_value', 3000]]
+  }, resolve));
+
+  let tab = yield BrowserTestUtils.openNewForegroundTab(gBrowser, "https://example.com");
+  let browser = gBrowser.selectedBrowser;
+
+  // Make the tab a background tab, so that setInterval will be throttled.
+  yield BrowserTestUtils.openNewForegroundTab(gBrowser);
+
+  let time = yield ContentTask.spawn(browser, null, function () {
+    return new Promise(resolve => {
+      let start = content.performance.now();
+      let id = content.window.setInterval(function() {
+        let end = content.performance.now();
+        content.window.clearInterval(id);
+        resolve(end - start);
+      }, 0);
+    });
+  });
+
+  ok(time > 2000, "Interval is throttled with no webaudio (" + time + " ms)");
+
+  time = yield ContentTask.spawn(browser, null, function () {
+    return new Promise(resolve => {
+      // Start playing audio, save it on the window so it doesn't get GCed
+      let audioCtx = content.window.audioCtx = new content.window.AudioContext();
+      let oscillator = audioCtx.createOscillator();
+      oscillator.type = 'square';
+      oscillator.frequency.value = 3000;
+      oscillator.start();
+
+      let start = content.performance.now();
+      let id = content.window.setInterval(function() {
+        let end = content.performance.now();
+        content.window.clearInterval(id);
+        oscillator.stop();
+        resolve(end - start);
+      }, 0);
+    });
+  });
+
+  ok(time < 1000, "Interval is not throttled with audio playing (" + time + " ms)");
+
+  // Destroy the oscillator, but not the audio context
+  yield new Promise(resolve => SpecialPowers.exactGC(browser.contentWindow, resolve));
+
+  time = yield ContentTask.spawn(browser, null, function () {
+    return new Promise(resolve => {
+      let start = content.performance.now();
+      let id = content.window.setInterval(function() {
+        let end = content.performance.now();
+        content.window.clearInterval(id);
+        resolve(end - start);
+      }, 0);
+    });
+  });
+
+  ok(time > 2000, "Interval is throttled with audio stopped (" + time + " ms)");
+
+  while (gBrowser.tabs.length > 1)
+    gBrowser.removeCurrentTab();
+});