private void executeSync(@Nonnull Runnable runnable) {
        if (ThreadContext.forCurrentThread() == ThreadContext.SYNC) {
            HelperExceptions.wrapSchedulerTask(runnable).run();
        } else {
            HelperExecutors.sync().execute(runnable);
        }
    }
The completable future backing this promise
helper/src/main/java/me/lucko/helper/promise/HelperPromise.java