Bug 1545079 - Execute revive logic in operation thread. r=padenot

`IsStarted` may not be updated at the time `Revive()` method is executed since the update of the flag happens on the async operation. This will be the case if `Revive` is executed right after `Start`. When that happens the revive method asserts that the stream is started.

Differential Revision: https://phabricator.services.mozilla.com/D30889

--HG--
extra : moz-landing-system : lando

dom/media/GraphDriver.cpp

@@ -442,9 +442,12 @@ AsyncCubebTask::Run() {
       mDriver->CompleteAudioContextOperations(mOperation);
       break;
     }
-    case AsyncCubebOperation::START: {
-      LOG(LogLevel::Debug, ("%p: AsyncCubebOperation::START driver=%p",
+    case AsyncCubebOperation::REVIVE: {
+      LOG(LogLevel::Debug, ("%p: AsyncCubebOperation::REVIVE driver=%p",
                             mDriver->GraphImpl(), mDriver.get()));
+      if (mDriver->IsStarted()) {
+        mDriver->Stop();
+      }
       if (!mDriver->StartStream()) {
         LOG(LogLevel::Warning,
             ("%p: AsyncCubebOperation couldn't start the driver=%p.",
@@ -452,12 +455,6 @@ AsyncCubebTask::Run() {
       }
       break;
     }
-    case AsyncCubebOperation::STOP: {
-      LOG(LogLevel::Debug, ("%p: AsyncCubebOperation::STOP driver=%p",
-                            mDriver->GraphImpl(), mDriver.get()));
-      mDriver->Stop();
-      break;
-    }
     case AsyncCubebOperation::SHUTDOWN: {
       LOG(LogLevel::Debug, ("%p: AsyncCubebOperation::SHUTDOWN driver=%p",
                             mDriver->GraphImpl(), mDriver.get()));
@@ -745,19 +742,9 @@ void AudioCallbackDriver::Revive() {
   if (NextDriver()) {
     SwitchToNextDriver();
   } else {
-    LOG(LogLevel::Debug,
-        ("Starting audio threads for MediaStreamGraph %p from a new thread.",
-         mGraphImpl.get()));
-    if (IsStarted()) {
-      RefPtr<AsyncCubebTask> stopEvent =
-          new AsyncCubebTask(this, AsyncCubebOperation::STOP);
-      // This dispatches to a thread pool with a maximum of one thread thus it
-      // is guaranteed to be executed before the start event, right below.
-      stopEvent->Dispatch();
-    }
-    RefPtr<AsyncCubebTask> startEvent =
-        new AsyncCubebTask(this, AsyncCubebOperation::START);
-    startEvent->Dispatch();
+    RefPtr<AsyncCubebTask> reviveEvent =
+        new AsyncCubebTask(this, AsyncCubebOperation::REVIVE);
+    reviveEvent->Dispatch();
   }
 }
 
@@ -985,9 +972,20 @@ long AudioCallbackDriver::DataCallback(const AudioDataValue* aInputBuffer,
   return aFrames;
 }
 
+static const char* StateToString(cubeb_state aState) {
+  switch (aState) {
+    case CUBEB_STATE_STARTED: return "STARTED";
+    case CUBEB_STATE_STOPPED: return "STOPPED";
+    case CUBEB_STATE_DRAINED: return "DRAINED";
+    case CUBEB_STATE_ERROR: return "ERROR";
+    default:
+      MOZ_CRASH("Unexpected state!");
+  }
+}
+
 void AudioCallbackDriver::StateCallback(cubeb_state aState) {
   MOZ_ASSERT(!OnGraphThread());
-  LOG(LogLevel::Debug, ("AudioCallbackDriver State: %d", aState));
+  LOG(LogLevel::Debug, ("AudioCallbackDriver State: %s", StateToString(aState)));
 
   // Clear the flag for the not running
   // states: stopped, drained, error.

dom/media/GraphDriver.h

@@ -12,6 +12,7 @@
 #include "AudioSegment.h"
 #include "SelfRef.h"
 #include "mozilla/Atomics.h"
+#include "mozilla/dom/AudioContext.h"
 #include "mozilla/SharedThreadPool.h"
 #include "mozilla/StaticPtr.h"
 
@@ -322,7 +323,7 @@ struct StreamAndPromiseForOperation {
   dom::AudioContextOperationFlags mFlags;
 };
 
-enum class AsyncCubebOperation { INIT, START, STOP, SHUTDOWN };
+enum class AsyncCubebOperation { INIT, REVIVE, SHUTDOWN };
 enum class AudioInputType { Unknown, Voice };
 
 /**