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;

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1. public class TodoTimer {  
2.     static Logger log = SimpleLogger.getLogger(TodoTimer.class);  
3.   
4.     private TodoTimer() {  
5.     }  
6.   
7.     /** 
8.      * 定时操作线程 
9.      */  
10.     private final static Runnable TodoOperation = new Runnable() {  
11.         public void run() {  
12.             try {  
13.                 semaphore.acquire();  
14.   
15.                 TodoManager.operate();  
16.             } catch (InterruptedException e) {  
17.                 e.printStackTrace();  
18.             } finally {  
19.                 semaphore.release();  
20.             }  
21.         }  
22.     };  
23.   
24.     /** 
25.      * 同步信号量 
26.      */  
27.     private static final Semaphore semaphore = new Semaphore(1);  
28.   
29.     /** 
30.      * 定时执行 
31.      */  
32.     private static ScheduledExecutorService scheduler = null;  
33.   
34.     /** 
35.      * 启动定时器 
36.      */  
37.     public static void start() {  
38.           
39.         if (scheduler == null) {  
40.             scheduler = Executors.newScheduledThreadPool(1);  
41.               
42.             synchronized (scheduler) {  
43.               
44.                 /* 
45.                  * TODO 设置定时器启动时间和间隔 
46.                  */  
47.                 scheduler.scheduleAtFixedRate(TodoOperation, 20, 60*5, TimeUnit.SECONDS);  
48.                 log.debug("启动TODO定时器!");  
49.             }  
50.               
51.         } else {  
52.             log.warn("TODO定时器正在运行!");  
53.         }  
54.           
55.     }  
56.   
57.     /** 
58.      * 停止定时器 
59.      */  
60.     public static void stop() {  
61.         synchronized (scheduler) {  
62.             if (scheduler != null && !scheduler.isShutdown()) {  
63.                 scheduler.shutdown();  
64.                 scheduler = null;  
65.                 log.debug("关闭TODO定时器!");  
66.             }  
67.         }  
68.     }  
69.   
70.     /** 
71.      * 重启定时器 
72.      */  
73.     public static void restart() {  
74.         stop();  
75.         start();  
76.     }  
77.   
78.     /** 
79.      * 手动触发 
80.      */  
81.     public static void trigger() {  
82.         TodoOperation.run();  
83.     }  
84. }  

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();}}