Merge 142687

Source/WebCore/Modules/webaudio/PannerNode.cpp

Index: Source/WebCore/Modules/webaudio/PannerNode.cpp
===================================================================
--- Source/WebCore/Modules/webaudio/PannerNode.cpp	(revision 143082)
+++ Source/WebCore/Modules/webaudio/PannerNode.cpp	(working copy)
@@ -104,21 +104,28 @@
         return;
     }
 
-    // Apply the panning effect.
-    double azimuth;
-    double elevation;
-    getAzimuthElevation(&azimuth, &elevation);
-    m_panner->pan(azimuth, elevation, source, destination, framesToProcess);
+    // The audio thread can't block on this lock, so we call tryLock() instead.
+    MutexTryLocker tryLocker(m_pannerLock);
+    if (tryLocker.locked()) {
+        // Apply the panning effect.
+        double azimuth;
+        double elevation;
+        getAzimuthElevation(&azimuth, &elevation);
+        m_panner->pan(azimuth, elevation, source, destination, framesToProcess);
 
-    // Get the distance and cone gain.
-    double totalGain = distanceConeGain();
+        // Get the distance and cone gain.
+        double totalGain = distanceConeGain();
 
-    // Snap to desired gain at the beginning.
-    if (m_lastGain == -1.0)
-        m_lastGain = totalGain;
+        // Snap to desired gain at the beginning.
+        if (m_lastGain == -1.0)
+            m_lastGain = totalGain;
         
-    // Apply gain in-place with de-zippering.
-    destination->copyWithGainFrom(*destination, &m_lastGain, totalGain);
+        // Apply gain in-place with de-zippering.
+        destination->copyWithGainFrom(*destination, &m_lastGain, totalGain);
+    } else {
+        // Too bad - The tryLock() failed. We must be in the middle of changing the panner.
+        destination->zero();
+    }
 }
 
 void PannerNode::reset()
@@ -185,6 +192,9 @@
     case EQUALPOWER:
     case HRTF:
         if (!m_panner.get() || model != m_panningModel) {
+            // This synchronizes with process().
+            MutexLocker processLocker(m_pannerLock);
+            
             OwnPtr<Panner> newPanner = Panner::create(model, sampleRate());
             m_panner = newPanner.release();
             m_panningModel = model;