fix wasm build. (#9312)

The new AsyncJobQueue can't work with wasm, which doesn't support 
threads.

filament/src/FrameInfo.cpp

@@ -173,6 +173,12 @@ void FrameInfoManager::endFrame(DriverApi& driver) noexcept {
         // backend frame end-time
         front.backendEndFrame = std::chrono::steady_clock::now();
 
+        if (UTILS_UNLIKELY(!jobQueue.isValid())) {
+            front.gpuFrameComplete = {};
+            front.ready.store(true, std::memory_order_release);
+            return;
+        }
+
         // now launch a job that'll wait for the gpu to complete
         jobQueue.push([&driver, &front] {
             FenceStatus const status = driver.fenceWait(front.fence, FENCE_WAIT_FOR_EVER);

libs/utils/include/utils/AsyncJobQueue.h

@@ -48,13 +48,17 @@ public:
     // adds a job to the queue. no-op if drainAndExit() was called.
     void push(Job&& job);
 
+    bool isValid() const noexcept;
+
 private:
+#if !defined(__EMSCRIPTEN__)
     using Container = std::vector<Job>;
     std::thread mThread;
     Mutex mLock; // NOLINT(*-include-cleaner)
     Condition mCondition; // NOLINT(*-include-cleaner)
     Container mQueue;
     bool mExitRequested = false;
+#endif
 };
 
 } // namespace utils

libs/utils/src/AsyncJobQueue.cpp

@@ -26,6 +26,7 @@
 namespace utils {
 
 AsyncJobQueue::AsyncJobQueue(const char* name, Priority priority) {
+#if !defined(__EMSCRIPTEN__)
     mQueue.reserve(2);
     mThread = std::thread([this, name, priority]() {
         JobSystem::setThreadName(name);
@@ -50,13 +51,17 @@ AsyncJobQueue::AsyncJobQueue(const char* name, Priority priority) {
             }
         } while (!exitRequested);
     });
+#endif
 }
 
 AsyncJobQueue::~AsyncJobQueue() noexcept {
+#if !defined(__EMSCRIPTEN__)
     assert_invariant(mQueue.empty());
+#endif
 }
 
 void AsyncJobQueue::push(Job&& job) {
+#if !defined(__EMSCRIPTEN__)
     std::unique_lock lock(mLock);
     if (UTILS_UNLIKELY(mExitRequested)) {
         LOG(WARNING) << "AsyncJobQueue::push() called after drainAndExit()";
@@ -67,9 +72,20 @@ void AsyncJobQueue::push(Job&& job) {
         lock.unlock();
         mCondition.notify_one();
     }
+#endif
 }
 
+bool AsyncJobQueue::isValid() const noexcept {
+#if !defined(__EMSCRIPTEN__)
+    return mThread.joinable();
+#else
+    return false;
+#endif
+}
+
+
 void AsyncJobQueue::drainAndExit() {
+#if !defined(__EMSCRIPTEN__)
     std::unique_lock lock(mLock);
     // we request the service thread to exit, but we're guaranteed that it'll only exit
     // after all current callbacks are processed. In addition, once mExitRequested is set,
@@ -80,6 +96,7 @@ void AsyncJobQueue::drainAndExit() {
     if (mThread.joinable()) {
         mThread.join();
     }
+#endif
 }
 
 } // namespace utils