Java ScheduledExecutorService ScheduleWithFixedDelay是否在某些迭代后添加意外延遲？

Question

我在兩個窗口的2 m / c上運行了調度程序，但配置不同-

public class testScheduling {
    static boolean header = false;
    static ScheduledExecutorService m_scheduleService;
    public static void main(String[] args) throws IOException {

        WorkerThread worker = new WorkerThread();
        m_scheduleService = Executors.newScheduledThreadPool(1);

        m_scheduleService.scheduleWithFixedDelay(worker, 1, 1,  TimeUnit.MILLISECONDS);

    }



     static public class WorkerThread implements Runnable{

            public WorkerThread(){
            }

            @Override
            public void run() {
                try {
                    processCommand();
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    System.out.println("something wrong in thread");
                    e.printStackTrace();
                }
            }

            private void processCommand() throws InterruptedException {
                Date d = new Date();
                System.out.println("print ...." + Utility.getDateToString(d));

            }

        }
}

在1 m / c上，結果是-

print ....2016-01-28 15:42:45.289
print ....2016-01-28 15:42:45.289
print ....2016-01-28 15:42:45.289
print ....2016-01-28 15:42:45.289
print ....2016-01-28 15:42:45.289
print ....2016-01-28 15:42:45.289
print ....2016-01-28 15:42:45.289
print ....2016-01-28 15:42:45.299
print ....2016-01-28 15:42:45.299
print ....2016-01-28 15:42:45.299
print ....2016-01-28 15:42:45.299
print ....2016-01-28 15:42:45.299

----經過一定的間隔10毫秒后。

在另一個m / c上，結果是

print ....2016-01-28 05:06:54.239
print ....2016-01-28 05:06:54.239
print ....2016-01-28 05:06:54.239
print ....2016-01-28 05:06:54.239
print ....2016-01-28 05:06:54.239
print ....2016-01-28 05:06:54.239
print ....2016-01-28 05:06:54.255
print ....2016-01-28 05:06:54.255
print ....2016-01-28 05:06:54.255
print ....2016-01-28 05:06:54.255
print ....2016-01-28 05:06:54.255
print ....2016-01-28 05:06:54.255

-某些迭代后的第二m / c顯示差異為16 ms。

為什么2個不同的m / c會有這種差異？ 為什么經過一些迭代后會有很長的延遲？ 可以消除這種意外的延遲嗎？

Answer 1

您不能期望Scheduler（在一台或多台計算機上）每次都完全同時運行。

我引用了ScheduledExecutorService Java文檔中的以下警告

Beware however that expiration of a relative delay need not coincide with the current Date at 
which the task is enabled due to network time synchronization protocols, clock drift, 
or other factors.

參考Java文檔鏈接

NTP應該能夠幫助您了解原因。