java.util.concurrent中的几种同步工具类

  

  java.util.concurrent并发包中提供了一系列的的同步工具类,这些基础类不管是否能在项目中使用到,了解一下使用方法和原理对java程序员来说都是有必要的。博主在看《java并发编程实战》这本书中提到了其中几个工具类,本文就对这些类进行简单的描述。

  CyclicBarrier(栅栏)

  4个朋友约好下班一起玩吃鸡,分别是M4,AWM,SKS,WIN94。这四个哥们下班时间不一样,决定好一个时间一起上号搞。

 

  大家约好到家就开游戏,必须珍惜生命,争分夺秒玩游戏。

  我们用栅栏来模仿一下场景:  

 1 public class CyclicBarrierTest {
 2 
 3     private static CyclicBarrier barrier = new CyclicBarrier(4);
 4 
 5     private static class EatChickenPlayer extends Thread {
 6 
 7         private String name;
 8 
 9         //下班时间
10         private Long offWorkTime;
11 
12         public EatChickenPlayer(String name, Long time) {
13             this.name = name;
14             this.offWorkTime = time;
15         }
16 
17         @Override
18         public void run() {
19             Timer timer = new Timer();
20             timer.schedule(new TimerTask() {
21                 @Override
22                 public void run() {
23                     System.out.println(name + ":我上号了");
24                     try {
25                         barrier.await();
26                         System.out.println(name + ":开打开打");
27                     } catch (Exception e) {
28                         e.printStackTrace();
29                     }
30                 }
31             }, offWorkTime);
32         }
33     }
34 
35     public static void main(String[] args) {
36         EatChickenPlayer m416 = new EatChickenPlayer("m416", 3000L);
37         EatChickenPlayer AWM = new EatChickenPlayer("AWM", 6000L);
38         EatChickenPlayer SKS = new EatChickenPlayer("SKS", 9000L);
39         EatChickenPlayer win94 = new EatChickenPlayer("win94", 4000L);
40         m416.start();
41         AWM.start();
42         SKS.start();
43         win94.start();
44     }
45 }

  运行一下代码,感受一下,

  

  栅栏通常阻塞一系列线程,当所有需要的线程都达到栅栏位置,才能继续执行。所以,栅栏可以理解为等待其他的线程到达对应的位置,在一起执行。

  在做一些并发测试的时候,有时候需要所有线程都执行到相应的位置,让它们同时执行。而且栅栏是可以重复利用的,当栅栏开放后,栅栏会进行重置,然后对后续的线程进行拦截。如果await调用超时,或者await的线程被中断,栅栏就被认为是打破了,所有await的线程都会中止并且抛出BrokenBarrierException。如果成功通过栅栏,那么await将为每个线程返回一个唯一的到达索引号,我们可以通过索引来选举一个领导线程。并在下一次循环中,通过领导线程执行一些特殊工作。

  CountDownLatch(闭锁)

  好不容易,四个人都到到齐了,纷纷上号。要进行游戏,必须等队伍里所有人都点击准备完成,游戏才能开始。这种时候可以时候,我们可以使用闭锁来实现这种业务场景。

 1 public class CountDownLatchTest {
 2 
 3     private static CountDownLatch countDownLatch = new CountDownLatch(4);
 4 
 5     public static class EatChicken extends Thread {
 6 
 7         private String name;
 8 
 9         private int time;
10 
11         public EatChicken(String name, int time) {
12             this.name = name;
13             this.time = time;
14         }
15 
16         @Override
17         public void run() {
18             System.out.println(name + "准备" + time + "秒");
19             try {
20                 SECONDS.sleep(time);
21             } catch (InterruptedException e) {
22                 e.printStackTrace();
23             }
24             System.out.println(name + "衣服换好了");
25             countDownLatch.countDown();
26         }
27     }
28     
29     public static void main(String[] args) throws InterruptedException {
30         System.out.println("-----等待所有人准备-----");
31         EatChicken m416 = new EatChicken("m416", 1);
32         EatChicken AWM = new EatChicken("AWM", 2);
33         EatChicken SKS = new EatChicken("SKS", 2);
34         EatChicken win94 = new EatChicken("win94", 3);
35         m416.start();
36         AWM.start();
37         SKS.start();
38         win94.start();
39 
40         countDownLatch.await();
41         System.out.println("-----所有人准备好了-----");
42         System.out.println("-----游戏开始-----");
43     }

   运行程序:

  

  闭锁初看跟栅栏非常相似,它们作为工具类,都能作为屏障,等待线程执行到一定的地方。闭锁跟栅栏的区别,就是闭锁是一次性的,当闭锁完全打开后就不能关闭了。栅栏打开之后,放行等待之后,栅栏就被重置,等待下一次开启。闭锁使用countDown()的时候,线程不会阻塞,继续运行。栅栏没有类似的countDown()方法,使用await()的时候,还需要等待的线程数-1,直到需要等待的线程数为0的时候,栅栏打开。

  Semaphore(信号量)

  有的时候,不仅这四位老哥去玩,时不时的M24也要来一起玩。这个时间,就只能大家一起抢位置了。没能挤进队伍的老哥内心百感交集,欲说还休。

  

  我们可以用信号量来模拟。

 1 public class SemaphoreTest {
 2 
 3     private static Semaphore semaphore = new Semaphore(4);
 4 
 5     private static class EatChickenPlayer extends Thread {
 6 
 7         private String name;
 8 
 9 
10         public EatChickenPlayer(String name) {
11             this.name = name;
12         }
13 
14         @Override
15         public void run() {
16             if (semaphore.tryAcquire()) {
17                 System.out.println(name + ":我进入游戏啦");
18             } else {
19                 System.out.println(name + ":卧槽,队伍满了");
20             }
21         }
22     }
23 
24     public static void main(String[] args) throws InterruptedException {
25         EatChickenPlayer m416 = new EatChickenPlayer("m416");
26         EatChickenPlayer AWM = new EatChickenPlayer("AWM");
27         EatChickenPlayer SKS = new EatChickenPlayer("SKS");
28         EatChickenPlayer win94 = new EatChickenPlayer("win94");
29         EatChickenPlayer M24 = new EatChickenPlayer("M24");
30         m416.start();
31         AWM.start();
32         SKS.start();
33         win94.start();
34         M24.start();
35     }

 

  运行一下代码:  

  

  信号量用来控制同时访问某特定资源的操作数量。通过acquire()阻塞获取资格。或者使用tryAcquire()方法获取,及时返回结果,获取权限成功则返回ture,获取失败返回false。当权限已经使用完毕后,调用release()或者release(int permits) 方法释放权限。

  FutureTask

  游戏终于开始了,落地的时候,发现有四个房子,四位胸怀吃鸡的老哥分配好各走一个房子收集里面的东西。收集出来之后一起分东西。这里把每个老哥去房子里舔装备作为一个Task。我们用FutureTask来模拟一下这个场景:

  

  1 package com.chinaredstar.jc.lock;
  2 
  3 import java.util.ArrayList;
  4 import java.util.List;
  5 import java.util.Map;
  6 import java.util.Random;
  7 import java.util.concurrent.*;
  8 import java.util.stream.Collectors;
  9 
 10 public class FutureTaskTest {
 11 
 12     /**
 13      * 固定的4线程,线程池
 14      */
 15     private static ExecutorService threadPoolExecutor = Executors.newFixedThreadPool(4);
 16 
 17     static class Equipment {
 18         /**
 19          * 这里简单模拟一下,
 20          * 1、子弹 2、枪械 3、药包
 21          */
 22         private Integer type;
 23 
 24         /**
 25          * 数量
 26          */
 27         private Integer num;
 28 
 29         public Equipment(Integer type, Integer num) {
 30             this.type = type;
 31             this.num = num;
 32         }
 33 
 34         public Integer getType() {
 35             return type;
 36         }
 37 
 38         public void setType(Integer type) {
 39             this.type = type;
 40         }
 41 
 42         public Integer getNum() {
 43             return num;
 44         }
 45 
 46         public void setNum(Integer num) {
 47             this.num = num;
 48         }
 49 
 50 
 51     }
 52 
 53     /**
 54      * 舔装备人物类
 55      */
 56     static class CollectTask implements Callable {
 57         private String name;
 58 
 59         public CollectTask(String name) {
 60             this.name = name;
 61         }
 62 
 63         @Override
 64         public List<Equipment> call() throws Exception {
 65             return generatorEquipment(name);
 66         }
 67     }
 68 
 69     public static List<Equipment> generatorEquipment(String name) {
 70 
 71         List<Equipment> list = new ArrayList<>();
 72 
 73         Random r = new Random();
 74         //子弹
 75         Equipment bullet = new Equipment(1, r.nextInt(100));
 76         list.add(bullet);
 77         System.out.println(name + ":捡到子弹" + bullet.num + "发");
 78         //
 79         Equipment gun = new Equipment(2, r.nextInt(3));
 80         System.out.println(name + ":捡到枪" + gun.num + " 把");
 81         list.add(gun);
 82         //药包
 83         Equipment bandage = new Equipment(3, r.nextInt(10));
 84         System.out.println(name + ":捡到绷带" + bandage.num + " 个");
 85         list.add(bandage);
 86         return list;
 87     }
 88 
 89     public static void main(String[] args) throws ExecutionException, InterruptedException {
 90         //生成任务
 91         CollectTask AWM = new CollectTask("AWM");
 92         CollectTask m416 = new CollectTask("m416");
 93         CollectTask SKS = new CollectTask("SKS");
 94         CollectTask win94 = new CollectTask("win94");
 95         //生成任务交给线程池
 96         Future AWM_future = threadPoolExecutor.submit(AWM);
 97         Future m416_future = threadPoolExecutor.submit(m416);
 98         Future SKS_future = threadPoolExecutor.submit(SKS);
 99         Future win94_future = threadPoolExecutor.submit(win94);
100 
101         //结果放在一起
102         List<Future> futureList = new ArrayList<>();
103         futureList.add(AWM_future);
104         futureList.add(m416_future);
105         futureList.add(SKS_future);
106         futureList.add(win94_future);
107 
108         //结果统一在一起
109         List<Equipment> taskResultList = new ArrayList<>();
110         for (Future<List<Equipment>> future : futureList) {
111             taskResultList.addAll(future.get());
112         }
113 
114         //打印出来看看都有些啥
115         Map<Integer, Integer> tolal = taskResultList.stream().collect(Collectors.groupingBy(
116                 Equipment::getType, Collectors.summingInt(Equipment::getNum)));
117         tolal.entrySet();
118         for (Map.Entry<Integer, Integer> entry : tolal.entrySet()) {
119             if (entry.getKey() == 1) {
120                 System.out.println("总共有子弹:" + entry.getValue());
121             }
122             if (entry.getKey() == 2) {
123                 System.out.println("总共有枪:" + entry.getValue());
124             }
125             if (entry.getKey() == 3) {
126                 System.out.println("总共有药包:" + entry.getValue());
127             }
128         }
129 
130     }
131 
132 }

  运行后的代码结果: 

  

  

  

posted on 2018-08-06 10:08  阿姆斯特朗回旋炮  阅读(1546)  评论(0编辑  收藏

导航