ScheduledExecutorService中scheduleAtFixedRate方法的同步

               

因为scheduleAtFixedRate是指定频率执行方法，若方法的执行时间大于指定的间隔时间，将会发生，同一时间点 ，执行方法N 次。

所以需要使用同步方法才确保并发操作的安全性。

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;

public class TodoTimer { static Logger log = SimpleLogger.getLogger(TodoTimer.class); private TodoTimer() { } /**  * 定时操作线程  */ private final static Runnable TodoOperation = new Runnable() {  public void run() {   try {    semaphore.acquire();    TodoManager.operate();   } catch (InterruptedException e) {    e.printStackTrace();   } finally {    semaphore.release();   }  } }; /**  * 同步信号量  */ private static final Semaphore semaphore = new Semaphore(1); /**  * 定时执行  */ private static ScheduledExecutorService scheduler = null; /**  * 启动定时器  */ public static void start() {    if (scheduler == null) {   scheduler = Executors.newScheduledThreadPool(1);      synchronized (scheduler) {       /*     * TODO 设置定时器启动时间和间隔     */    scheduler.scheduleAtFixedRate(TodoOperation, 20, 60*5, TimeUnit.SECONDS);    log.debug("启动TODO定时器!");   }     } else {   log.warn("TODO定时器正在运行!");  }   } /**  * 停止定时器  */ public static void stop() {  synchronized (scheduler) {   if (scheduler != null && !scheduler.isShutdown()) {    scheduler.shutdown();    scheduler = null;    log.debug("关闭TODO定时器!");   }  } } /**  * 重启定时器  */ public static void restart() {  stop();  start(); } /**  * 手动触发  */ public static void trigger() {  TodoOperation.run(); }}

           

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