public static UiThreadImmediateExecutorService getInstance() {
    if (sInstance == null) {
      sInstance = new UiThreadImmediateExecutorService();
    }
    return sInstance;
  }
An {@link ExecutorService} that is backed by the application's main looper.

<p>If the execute is called from the thread of the application's main looper, it will be executed
synchronously.
fbcore/src/main/java/com/facebook/common/executors/UiThreadImmediateExecutorService.java