Prevent deadlock when exiting WebXR/WebVR

app/src/common/shared/org/mozilla/vrbrowser/VRBrowserActivity.java

@@ -1048,7 +1048,7 @@ void onEnterWebXR() {
 
     @Keep
     @SuppressWarnings("unused")
-    void onExitWebXR() {
+    void onExitWebXR(long aCallback) {
         if (Thread.currentThread() == mUiThread) {
             return;
         }
@@ -1070,6 +1070,9 @@ void onExitWebXR() {
             if (!mWindows.isPaused()) {
                 Log.d(LOGTAG, "Compositor resume begin");
                 mWindows.resumeCompositor();
+                if (aCallback != 0) {
+                    queueRunnable(() -> runCallbackNative(aCallback));
+                }
                 Log.d(LOGTAG, "Compositor resume end");
             }
         }, 20);

app/src/main/cpp/ExternalVR.cpp

@@ -378,9 +378,17 @@ ExternalVR::SetCompositorEnabled(bool aEnabled) {
   }
   m.compositorEnabled = aEnabled;
   if (aEnabled) {
-    VRBrowser::OnExitWebXR();
+    // Set suppressFrames to avoid a deadlock between the sync surfaceChanged call
+    // and the gecko VRManager SubmitFrame result wait.
+    m.system.displayState.suppressFrames = true;
+    PushSystemState();
+    VRBrowser::OnExitWebXR([=]{
+        m.system.displayState.suppressFrames = false;
+        PushSystemState();
+    });
   } else {
-    // Set suppressFrames to avoid a deadlock between the compositor sync pause call and the gfxVRExternal SubmitFrame result wait.
+    // Set suppressFrames to avoid a deadlock between the compositor sync pause call
+    // and the gecko VRManager SubmitFrame result wait.
     m.system.displayState.suppressFrames = true;
     m.system.displayState.lastSubmittedFrameId = 0;
     m.lastFrameId = 0;

app/src/main/cpp/VRBrowser.cpp

@@ -33,7 +33,7 @@ const char* const kRegisterExternalContextSignature = "(J)V";
 const char* const kOnEnterWebXRName = "onEnterWebXR";
 const char* const kOnEnterWebXRSignature = "()V";
 const char* const kOnExitWebXRName = "onExitWebXR";
-const char* const kOnExitWebXRSignature = "()V";
+const char* const kOnExitWebXRSignature = "(J)V";
 const char* const kOnDismissWebXRInterstitialName = "onDismissWebXRInterstitial";
 const char* const kOnDismissWebXRInterstitialSignature = "()V";
 const char* const kOnWebXRRenderStateChangeName = "onWebXRRenderStateChange";
@@ -263,9 +263,13 @@ VRBrowser::OnEnterWebXR() {
 }
 
 void
-VRBrowser::OnExitWebXR() {
+VRBrowser::OnExitWebXR(const std::function<void()>& aCallback) {
   if (!ValidateMethodID(sEnv, sActivity, sOnExitWebXR, __FUNCTION__)) { return; }
-  sEnv->CallVoidMethod(sActivity, sOnExitWebXR);
+  jlong callback = 0;
+  if (aCallback) {
+    callback = reinterpret_cast<jlong>(new std::function<void()>(aCallback));
+  }
+  sEnv->CallVoidMethod(sActivity, sOnExitWebXR, callback);
   CheckJNIException(sEnv, __FUNCTION__);
 }
 

app/src/main/cpp/VRBrowser.h

@@ -29,7 +29,7 @@ void HandleMoveEnd(jint aWidgetHandle, jfloat aX, jfloat aY, jfloat aZ, jfloat a
 void HandleBack();
 void RegisterExternalContext(jlong aContext);
 void OnEnterWebXR();
-void OnExitWebXR();
+void OnExitWebXR(const std::function<void()>& aCallback);
 void OnDismissWebXRInterstitial();
 void OnWebXRRenderStateChange(const bool aRendering);
 void RenderPointerLayer(jobject aSurface, const std::function<void()>& aFirstCompositeCallback);