Bug 1665225 - Remove unnecessary to-main-thread dispatch r=alwu

The SMTC-thumbnail-update task is dispatched to main-thread from the
on-complete callback of the async image storing operation. However, the
callback is actually on the main-thread itself so the
thumbnail-update-task can be executed in that callback directly instead
of being dispatched. The task should be finished slightly faster if the
task dispatch is replaced by executing the task.

Differential Revision: https://phabricator.services.mozilla.com/D90331

widget/windows/WindowsSMTCProvider.cpp

@@ -596,6 +596,8 @@ void WindowsSMTCProvider::LoadImage(const char* aImageData,
       [this, self = RefPtr<WindowsSMTCProvider>(this),
        aImageUrl = nsString(mProcessingUrl)](
           IAsyncOperation<unsigned int>* aAsyncOp, AsyncStatus aStatus) {
+        MOZ_ASSERT(NS_IsMainThread());
+
         if (aStatus != AsyncStatus::Completed) {
           LOG("Asynchronous operation is not completed");
           return E_ABORT;
@@ -609,9 +611,8 @@ void WindowsSMTCProvider::LoadImage(const char* aImageData,
           return hr;
         }
 
-        nsresult rv = UpdateThumbnailOnMainThread(aImageUrl);
-        if (NS_FAILED(rv)) {
-          LOG("Failed to dispatch a task to thumbnail update");
+        if (!UpdateThumbnail(aImageUrl)) {
+          LOG("Failed to update thumbnail");
         }
 
         // If an error occurs above:
@@ -689,34 +690,31 @@ void WindowsSMTCProvider::ClearThumbnail() {
   mThumbnailUrl = EmptyString();
 }
 
-nsresult WindowsSMTCProvider::UpdateThumbnailOnMainThread(
-    const nsAString& aUrl) {
-  return NS_DispatchToMainThread(
-      media::NewRunnableFrom([this, self = RefPtr<WindowsSMTCProvider>(this),
-                              aImageUrl = nsString(aUrl)] {
-        if (!IsOpened()) {
-          LOG("Abort the thumbnail update: SMTC is closed");
-          return NS_OK;
-        }
+bool WindowsSMTCProvider::UpdateThumbnail(const nsAString& aUrl) {
+  MOZ_ASSERT(NS_IsMainThread());
 
-        if (aImageUrl != mProcessingUrl) {
-          LOG("Abort the thumbnail update: The image from %s is out of date",
-              NS_ConvertUTF16toUTF8(aImageUrl).get());
-          return NS_OK;
-        }
+  if (!IsOpened()) {
+    LOG("Abort the thumbnail update: SMTC is closed");
+    return false;
+  }
 
-        mProcessingUrl = EmptyString();
+  if (aUrl != mProcessingUrl) {
+    LOG("Abort the thumbnail update: The image from %s is out of date",
+        NS_ConvertUTF16toUTF8(aUrl).get());
+    return false;
+  }
 
-        if (!SetThumbnail(aImageUrl)) {
-          LOG("Failed to update thumbnail");
-          return NS_OK;
-        }
+  mProcessingUrl = EmptyString();
+
+  if (!SetThumbnail(aUrl)) {
+    LOG("Failed to update thumbnail");
+    return false;
+  }
 
-        MOZ_ASSERT(mThumbnailUrl == aImageUrl);
-        LOG("The thumbnail is updated to the image from: %s",
-            NS_ConvertUTF16toUTF8(mThumbnailUrl).get());
-        return NS_OK;
-      }));
+  MOZ_ASSERT(mThumbnailUrl == aUrl);
+  LOG("The thumbnail is updated to the image from: %s",
+      NS_ConvertUTF16toUTF8(mThumbnailUrl).get());
+  return true;
 }
 
 void WindowsSMTCProvider::CancelPendingStoreAsyncOperation() const {

widget/windows/WindowsSMTCProvider.h

@@ -79,7 +79,7 @@ class WindowsSMTCProvider final : public mozilla::dom::MediaControlKeySource {
   bool SetThumbnail(const nsAString& aUrl);
   void ClearThumbnail();
 
-  nsresult UpdateThumbnailOnMainThread(const nsAString& aUrl);
+  bool UpdateThumbnail(const nsAString& aUrl);
   void CancelPendingStoreAsyncOperation() const;
 
   bool mInitialized = false;