protected final boolean offerTask(final Runnable task) {
        if (isShutdown()) {
            reject();
        }
        return this.taskQueue.offer(task);
    }
Add a task to the task queue, or throws a {@link RejectedExecutionException} if
this instance was shutdown before.
jraft-core/src/main/java/com/alipay/sofa/jraft/util/concurrent/MpscSingleThreadExecutor.java