Implement suspend/resume for AudioContext

Source/modules/webaudio/AudioContext.cpp

Index: Source/modules/webaudio/AudioContext.cpp
diff --git a/Source/modules/webaudio/AudioContext.cpp b/Source/modules/webaudio/AudioContext.cpp
index 69e4e8aea09bbec1185dc7349224f6e568ebe2c7..5ec8923f3a4c7a1b4e3334898dbddc78eda55f0d 100644
--- a/Source/modules/webaudio/AudioContext.cpp
+++ b/Source/modules/webaudio/AudioContext.cpp
@@ -30,6 +30,7 @@
 
 #include "bindings/core/v8/ExceptionMessages.h"
 #include "bindings/core/v8/ExceptionState.h"
+#include "bindings/core/v8/ScriptState.h"
 #include "core/dom/Document.h"
 #include "core/dom/ExceptionCode.h"
 #include "core/html/HTMLMediaElement.h"
@@ -101,6 +102,7 @@ AudioContext::AudioContext(Document* document)
     , m_isCleared(false)
     , m_isInitialized(false)
     , m_destinationNode(nullptr)
+    , m_isResolvingResumePromises(false)
     , m_automaticPullNodesNeedUpdating(false)
     , m_connectionCount(0)
     , m_audioThread(0)
@@ -121,6 +123,7 @@ AudioContext::AudioContext(Document* document, unsigned numberOfChannels, size_t
     , m_isCleared(false)
     , m_isInitialized(false)
     , m_destinationNode(nullptr)
+    , m_isResolvingResumePromises(false)
     , m_automaticPullNodesNeedUpdating(false)
     , m_connectionCount(0)
     , m_audioThread(0)
@@ -531,6 +534,40 @@ PeriodicWave* AudioContext::createPeriodicWave(Float32Array* real, Float32Array*
     return PeriodicWave::create(sampleRate(), real, imag);
 }
 
+void AudioContext::suspendContext()
+{
+    ASSERT(isMainThread());
+    AutoLocker locker(this);
+
+    if (m_destinationNode && !isOfflineContext())
+        m_destinationNode->stop();
+}
+
+ScriptPromise AudioContext::resumeContext(ScriptState* scriptState)
+{
+    ASSERT(isMainThread());
+    AutoLocker locker(this);
+
+    RefPtr<ScriptPromiseResolver> resolver = ScriptPromiseResolver::create(scriptState);
+
+    ScriptPromise promise = resolver->promise();
+
+    if (isOfflineContext()) {
+        // For offline context, just resolve the promise now.
+        resolver->resolve();
+    } else {
+        // Restart the destination node to pull on the audio graph.
+        if (m_destinationNode)
+            m_destinationNode->startRendering();
+
+        // Save the promise which will get resolved when the destination node starts pulling on the
+        // graph again.
+        m_resumePromises.append(resolver);
+    }
+
+    return promise;
+}
+
 void AudioContext::notifyNodeFinishedProcessing(AudioNode* node)
 {
     ASSERT(isAudioThread());
@@ -637,6 +674,8 @@ void AudioContext::handlePreRenderTasks()
         handleDirtyAudioNodeOutputs();
 
         updateAutomaticPullNodes();
+        resolvePromisesForResume();
+
         unlock();
     }
 }
@@ -802,6 +841,30 @@ void AudioContext::processAutomaticPullNodes(size_t framesToProcess)
         m_renderingAutomaticPullNodes[i]->processIfNecessary(framesToProcess);
 }
 
+void AudioContext::resolvePromisesForResumeOnMainThread()
+{
+    ASSERT(isMainThread);

[yhirano, 2014/10/08 01:12:14]

Please acquire the lock.

[yhirano, 2014/10/08 01:15:54]

Oh, I found AudioContext::lock is not callable from the main thread. You need to
protect shared member variables though. Maybe manipulating these variables in
the audio thread and passing them to this function via parameters works?

[Raymond Toy, 2014/10/14 17:16:59]

Done.

+
+    for (unsigned k = 0; k < m_resumePromises.size(); ++k)
+        m_resumePromises[k]->resolve();
+
+    m_resumePromises.clear();
+    m_isResolvingResumePromises = false;
+}
+
+void AudioContext::resolvePromisesForResume()
+{
+    ASSERT(isAudioThread());
+

[yhirano, 2014/10/08 01:12:14]

Please add a comment that the lock is already acquired.

[Raymond Toy, 2014/10/14 17:16:59]

Done.

+    // Resolve any pending promises created by resume(). Only do this we if haven't already started
+    // resolving these promises. This gets called very often and it takes some time use to resolve
+    // the promises in the main thread.
+    if (!m_isResolvingResumePromises && m_resumePromises.size() > 0) {
+        m_isResolvingResumePromises = true;
+        callOnMainThread(bind(&AudioContext::resolvePromisesForResumeOnMainThread, this));
+    }
+}
+
 const AtomicString& AudioContext::interfaceName() const
 {
     return EventTargetNames::AudioContext;