Avoid calling Context()->GetExecutionContext() on non-main threads in webaudio

Checking the existence of execution context is not thread safe. Instead,
let's check it on the handler sides (main thread).

Bug: 696905
Change-Id: I68a05ef9e32837f74ef1772d66631bfd104c7d5e
Reviewed-on: https://chromium-review.googlesource.com/746721Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Reviewed-by: Raymond Toy <rtoy@chromium.org>
Commit-Queue: Hajime Hoshi <hajimehoshi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512850}

third_party/WebKit/Source/modules/webaudio/AudioScheduledSourceNode.cpp

@@ -231,16 +231,16 @@ void AudioScheduledSourceHandler::FinishWithoutOnEnded() {
 void AudioScheduledSourceHandler::Finish() {
   FinishWithoutOnEnded();
 
-  if (Context()->GetExecutionContext()) {
-    task_runner_->PostTask(
-        BLINK_FROM_HERE,
-        CrossThreadBind(&AudioScheduledSourceHandler::NotifyEnded,
-                        WrapRefCounted(this)));
-  }
+  task_runner_->PostTask(
+      BLINK_FROM_HERE,
+      CrossThreadBind(&AudioScheduledSourceHandler::NotifyEnded,
+                      WrapRefCounted(this)));
 }
 
 void AudioScheduledSourceHandler::NotifyEnded() {
   DCHECK(IsMainThread());
+  if (!Context() || !Context()->GetExecutionContext())
+    return;
   if (GetNode())
     GetNode()->DispatchEvent(Event::Create(EventTypeNames::ended));
 }

third_party/WebKit/Source/modules/webaudio/MediaElementAudioSourceNode.cpp

@@ -203,12 +203,10 @@ void MediaElementAudioSourceHandler::Process(size_t number_of_frames) {
         // Print a CORS message, but just once for each change in the current
         // media element source, and only if we have a document to print to.
         maybe_print_cors_message_ = false;
-        if (Context()->GetExecutionContext()) {
-          task_runner_->PostTask(
-              BLINK_FROM_HERE,
-              CrossThreadBind(&MediaElementAudioSourceHandler::PrintCORSMessage,
-                              WrapRefCounted(this), current_src_string_));
-        }
+        task_runner_->PostTask(
+            BLINK_FROM_HERE,
+            CrossThreadBind(&MediaElementAudioSourceHandler::PrintCORSMessage,
+                            WrapRefCounted(this), current_src_string_));
       }
       output_bus->Zero();
     }

third_party/WebKit/Source/modules/webaudio/OfflineAudioDestinationNode.cpp

@@ -254,30 +254,26 @@ void OfflineAudioDestinationHandler::SuspendOfflineRendering() {
   DCHECK(!IsMainThread());
 
   // The actual rendering has been suspended. Notify the context.
-  if (Context()->GetExecutionContext()) {
-    task_runner_->PostTask(
-        BLINK_FROM_HERE,
-        CrossThreadBind(&OfflineAudioDestinationHandler::NotifySuspend,
-                        WrapRefCounted(this), Context()->CurrentSampleFrame()));
-  }
+  task_runner_->PostTask(
+      BLINK_FROM_HERE,
+      CrossThreadBind(&OfflineAudioDestinationHandler::NotifySuspend,
+                      WrapRefCounted(this), Context()->CurrentSampleFrame()));
 }
 
 void OfflineAudioDestinationHandler::FinishOfflineRendering() {
   DCHECK(!IsMainThread());
 
   // The actual rendering has been completed. Notify the context.
-  if (Context()->GetExecutionContext()) {
-    task_runner_->PostTask(
-        BLINK_FROM_HERE,
-        CrossThreadBind(&OfflineAudioDestinationHandler::NotifyComplete,
-                        WrapRefCounted(this)));
-  }
+  task_runner_->PostTask(
+      BLINK_FROM_HERE,
+      CrossThreadBind(&OfflineAudioDestinationHandler::NotifyComplete,
+                      WrapRefCounted(this)));
 }
 
 void OfflineAudioDestinationHandler::NotifySuspend(size_t frame) {
   DCHECK(IsMainThread());
 
-  if (Context())
+  if (Context() && Context()->GetExecutionContext())
     Context()->ResolveSuspendOnMainThread(frame);
 }
 
@@ -288,7 +284,7 @@ void OfflineAudioDestinationHandler::NotifyComplete() {
   render_thread_.reset();
 
   // The OfflineAudioContext might be gone.
-  if (Context())
+  if (Context() && Context()->GetExecutionContext())
     Context()->FireCompletionEvent();
 }
 

third_party/WebKit/Source/modules/webaudio/ScriptProcessorNode.cpp

@@ -213,7 +213,7 @@ void ScriptProcessorHandler::Process(size_t frames_to_process) {
       // We're late in handling the previous request. The main thread must be
       // very busy.  The best we can do is clear out the buffer ourself here.
       output_buffer->Zero();
-    } else if (Context()->GetExecutionContext()) {
+    } else {
       // With the realtime context, execute the script code asynchronously
       // and do not wait.
       if (Context()->HasRealtimeConstraint()) {
@@ -249,6 +249,9 @@ void ScriptProcessorHandler::Process(size_t frames_to_process) {
 void ScriptProcessorHandler::FireProcessEvent(unsigned double_buffer_index) {
   DCHECK(IsMainThread());
 
+  if (!Context() || !Context()->GetExecutionContext())
+    return;
+
   DCHECK_LT(double_buffer_index, 2u);
   if (double_buffer_index > 1)
     return;
@@ -260,7 +263,7 @@ void ScriptProcessorHandler::FireProcessEvent(unsigned double_buffer_index) {
     return;
 
   // Avoid firing the event if the document has already gone away.
-  if (GetNode() && Context() && Context()->GetExecutionContext()) {
+  if (GetNode()) {
     // This synchronizes with process().
     MutexLocker process_locker(process_event_lock_);
 
@@ -282,6 +285,9 @@ void ScriptProcessorHandler::FireProcessEventForOfflineAudioContext(
     WaitableEvent* waitable_event) {
   DCHECK(IsMainThread());
 
+  if (!Context() || !Context()->GetExecutionContext())
+    return;
+
   DCHECK_LT(double_buffer_index, 2u);
   if (double_buffer_index > 1) {
     waitable_event->Signal();
@@ -296,7 +302,7 @@ void ScriptProcessorHandler::FireProcessEventForOfflineAudioContext(
     return;
   }
 
-  if (GetNode() && Context() && Context()->GetExecutionContext()) {
+  if (GetNode()) {
     // We do not need a process lock here because the offline render thread
     // is locked by the waitable event.
     double playback_time = (Context()->CurrentSampleFrame() + buffer_size_) /