private void addWorkerIfNecessary() {
        if (this.idleWorkers.get() == 0) {
            synchronized (this.workers) {
                if (this.workers.isEmpty() || this.idleWorkers.get() == 0) {
                    this.addWorker();
                }
            }
        }
    }
Add a new Worker only if there are no idle worker.
metamorphosis-server-wrapper/src/main/java/com/taobao/metamorphosis/gregor/slave/OrderedThreadPoolExecutor.java