Java 并发编程实践基础 读书笔记： 第三章 使用 JDK 并发包构建程序

一，JDK并发包实际上就是指java.util.concurrent包里面的那些类和接口等

　　主要分为以下几类： 1，原子量；2，并发集合；3，同步器；4，可重入锁；5，线程池

二，原子量

　　原子变量主要有AtomicInteger，AtomicLong，AtomicBoolean等，

　　主要实现原理都是底层实现类CAS 即比较并交换，都有get,set,compareAndSet等方法，如++，--等也都是有自带方法实现

　　这些都是线程安全的，保证了多线程访问时候的可见性

　　

 1 import java.util.concurrent.atomic.AtomicLong;
 2 
 3 /**
 4  * StudySjms
 5  * 

 6  * Created by haozb on 2018/3/2.
 7  */
 8 public class AtomicAccount {
 9 
10     AtomicLong account;
11 
12     public AtomicAccount(long money) {
13         this.account = new AtomicLong(money);
14     }
15 
16     public void withDraw(long money,int sleepTime){
17         long oldValue = account.get();
18         if(oldValue >= money){
19             try {
20                 Thread.sleep(sleepTime);
21             } catch (Exception e) {
22 
23             }
24             if(account.compareAndSet(oldValue,oldValue-money)){
25                 System.out.println(Thread.currentThread().getName()+"扣钱成功");
26             }else{
27                 System.out.println(Thread.currentThread().getName()+"扣钱失败");
28             }
29         }else{
30             System.out.println("钱不够了");
31         }
32     }
33 
34     public static void main(String[] args) {
35         final AtomicAccount aa = new AtomicAccount(100);
36 
37         for (int i = 0; i < 2; i++) {
38             new Thread(new Runnable() {
39                 @Override
40                 public void run() {
41                     aa.withDraw(100,1000);
42                 }
43             }).start();
44         }
45     }
46 }

上面这个方法就是利用原子量解决多线程中计数不安全的例子;

三，并发集合

这个包里面有一个阻塞队列的接口BlockingQueue，阻塞的概念就是满了就不会再填充了，空了也不允许再取，

所有实现这个接口的队列都是线程安全的。

主要有ArrayBlockingQueue：一个由数组支持的有界队列

　　　LinkedBlockingQueue：一个由链接节点支持的可选有界队列

　　   PriorityBlockingQueue：一个由优先级堆支持的无界优先级队列

　　　DelayQueue ：一个由优先级堆支持的、基于时间的调度队列

ConcurrentMap 接口，ConcurrentHashMap， 这个实现类的方法是原子的，源代码里面是采用lock住put那一块代码。

CopyOnWriteArrayList，CopyOnWriteArraySet采用copy-on-write 模式

package copyonwrite;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;

public class CopyOnWriteDemo {
    @SuppressWarnings("unchecked")
    public static void main(String args[]) {
        String[] ss = {"aa", "bb", "cc"};
        List list1 = new CopyOnWriteArrayList(Arrays.asList(ss));
        List list2 = new ArrayList(Arrays.asList(ss));
        Iterator itor1 = list1.iterator();
        Iterator itor2 = list2.iterator();
        list1.add("New");
        list2.add("New");
        try {
            printAll(itor1);
        } catch (ConcurrentModificationException e) {
            System.err.println("Shouldn't get here");
        }
        try {
            printAll(itor2);
        } catch (ConcurrentModificationException e) {
            System.err.println("Will gethere.ConcurrentModificationException occurs !");
        }
    }

    @SuppressWarnings("unchecked")
    private static void printAll(Iterator itor) {
        while (itor.hasNext()) {
            System.out.println(itor.next());
        }
    }
}

 

运行结果如下：
Will get here.ConcurrentModificationException occurs!
aa
bb
cc

这个例子很好地说明了。

四，同步器

　　主要有CyclicBarrier：

　　1.它允许在涉及一组固定大小的线程的程序中，这些线程必须不时地互相等待

　　2.重要的属性就是参与者个数，另外最要方法是 await()。当所有线程都调用了 await()后，就表示这些线程都可以继续执行，否则就会等待

 1 package synchronizer;
 2 
 3 import java.text.SimpleDateFormat;
 4 import java.util.Date;
 5 import java.util.concurrent.BrokenBarrierException;
 6 import java.util.concurrent.CyclicBarrier;
 7 import java.util.concurrent.ExecutorService;
 8 import java.util.concurrent.Executors;
 9 
10 public class CyclicBarrierDemo {
11     /* 徒步需要的时间: Shenzhen, Guangzhou, Chongqing */
12     private static int[] timeForWalk = { 5, 8, 15 };
13     /* 自驾游 */
14     private static int[] timeForSelf = { 1, 3, 4 };
15     /* 旅游大巴 */
16     private static int[] timeForBus = { 2, 4, 6 };
17 
18     static String nowTime() /* 时间格式化 */
19     {
20         SimpleDateFormat sdf = new SimpleDateFormat( "HH:mm:ss" );
21         return(sdf.format( new Date() ) + ": ");
22     }
23 
24 
25     static class Tour implements Runnable {
26         private int[]        timeForUse;
27         private CyclicBarrier    barrier;
28         private String        tourName;
29 
30         public Tour( CyclicBarrier barrier, String tourName, int[] timeForUse )
31         {
32             this.timeForUse = timeForUse;
33             this.tourName    = tourName;
34             this.barrier    = barrier;
35         }
36 
37 
38         public void run()
39         {
40             try {
41                 Thread.sleep( timeForUse[0] * 1000 );
42                 System.out.println( nowTime() + tourName + "  ReachedShenenzh " );
43                 barrier.await();        /* 到达中转站后等待其他旅行团 */
44                 Thread.sleep( timeForUse[1] * 1000 );
45                 System.out.println( nowTime() + tourName + "  ReachedGuangzhou" );
46                 barrier.await();        /* 到达中转站后等待其他旅行团 */
47                 Thread.sleep( timeForUse[2] * 1000 );
48                 System.out.println( nowTime() + tourName + "  ReachedChonin" );
49                 barrier.await();        /* 到达中转站后等待其他旅行团 */
50             } catch ( InterruptedException e ) {
51             } catch ( BrokenBarrierException e ) {
52             }
53         }
54     }
55 
56     public static void main( String[] args )
57     {
58         /* 三个旅行团都到到达某一个站点后，执行下面的操作，表示都到齐了。 */
59         Runnable runner = new Runnable()
60         {
61             @Override
62             public void run()
63             {
64                 System.out.println( "we all are here." );
65             }
66         };
67         CyclicBarrier barrier = new CyclicBarrier( 3, runner );
68 /* 使用线程池 */
69         ExecutorService exec = Executors.newFixedThreadPool( 3 );
70         exec.submit( new Tour( barrier, "WalkTour", timeForWalk ) );
71         exec.submit( new Tour( barrier, "SelfTour", timeForSelf ) );
72         exec.submit( new Tour( barrier, "BusTour", timeForBus ) );
73         exec.shutdown();
74     }
75 }

 1 17:13:18: SelfTour Reached Shenzhen
 2 17 3:1 Bus :1 9: Tour Reached Shenzhen
 3 17 3:2 WalkTour Reached Shenzhen  :1 2:
 4 we all are here.
 5 17 3:2 SelfTour Reached Guangzhou  :1 5:
 6 17 3:2 BusTour Reached Guangzhou  :1 6:
 7 17 3:3 WalkTour Reached Guangzhou  :1 0:
 8 we all are here.
 9 17 3:3 SelfTour Reached Ch :1 4:  ongqing
10 17:13:36: BusTour Reached Chongqing
11 17:13:45: WalkTour Reached Chongqing
12 we all are here.

五，Future(接口)和FutureTask(实现类)

　　注：FutureTask实现了Runnable，所以可以通过线程池和Thread执行

　　使用他们的好处是可以获得线程的结果，和抛出异常，这种好处通过Callable的定义就知道了

1 public interface Callable {
2     /**
3      * Computes a result, or throws an exception if unable to do so.
4      *
5      * @return computed result
6      * @throws Exception if unable to compute a result
7      */
8     V call() throws Exception;
9 }

可以通过以下几种方式调用

 1 import java.util.concurrent.ExecutorService;
 2 import java.util.concurrent.Executors;
 3 import java.util.concurrent.Future;
 4 import java.util.concurrent.FutureTask;
 5 
 6 public class CallableTest {
 7 
 8     public static void main(String[] args) {
 9 //      //创建线程池  
10 //      ExecutorService es = Executors.newSingleThreadExecutor();  
11 //      //创建Callable对象任务  
12 //      CallableDemo calTask=new CallableDemo();  
13 //      //提交任务并获取执行结果  
14 //      Future future =es.submit(calTask);  
15 //      //关闭线程池  
16 //      es.shutdown();  
17 
18         //创建线程池  
19         ExecutorService es = Executors.newSingleThreadExecutor();
20         //创建Callable对象任务  
21         CallableDemo calTask=new CallableDemo();
22         //创建FutureTask  
23         FutureTask futureTask=new FutureTask(calTask);
24         //执行任务  
25         es.submit(futureTask);
26         //关闭线程池  
27         es.shutdown();
28         try {
29             Thread.sleep(2000);
30             System.out.println("主线程在执行其他任务");
31 
32             if(futureTask.get()!=null){
33                 //输出获取到的结果  
34                 System.out.println("futureTask.get()-->"+futureTask.get());
35             }else{
36                 //输出获取到的结果  
37                 System.out.println("futureTask.get()未获取到结果");
38             }
39 
40         } catch (Exception e) {
41             e.printStackTrace();
42         }
43         System.out.println("主线程在执行完成");
44     }
45 }  

六，ReentrantLock显示锁 也叫可重入锁; 必须在finally里面释放锁

　　实现方式：

1 Lock lock=new ReentrantLock();
2 lock.lock();
3 try{
4 // 更新对象状态
5 }
6 finally{
7 lock.unlock();
8 }

new的时候，有个参数，true或者false 决定了是不是公平锁，正常上不公平锁的性能比较好！

线程之间的交互，有一个类叫Condition：Condition 的方法与 wait 、notify 和 notifyAll 方法类似，分别命名为 await 、 signal 和 signalAll

后面会详细的介绍

 

七，ReadWriteLock

ReadWriteLock 维护了一对相关的锁，一个用于只读操作，另一个用于写入操作。只要没有 writer，读取锁可以由多个 reader 线程同时保持。写入锁是独占的

这个锁比互斥锁的性能上应该好些（读的频率大于写的频率）

  1 import java.util.Calendar;
  2 import java.util.Map;
  3 import java.util.TreeMap;
  4 import java.util.concurrent.locks.Lock;
  5 import java.util.concurrent.locks.ReentrantReadWriteLock;
  6 
  7 /**
  8  * StudySjms
  9  * 

 10  * Created by haozb on 2018/3/2.
 11  */
 12 public class ReadWriteLockDemo {
 13     private ReentrantReadWriteLock lock = null;
 14     private Lock readLock = null;// 读锁
 15     private Lock writeLock = null;// 写锁
 16     public int key = 100;
 17     public int index = 100;
 18     public Map dataMap = null;// 线程共享数据
 19 
 20     public ReadWriteLockDemo() {
 21         lock = new ReentrantReadWriteLock(true);
 22         readLock = lock.readLock();
 23         writeLock = lock.writeLock();
 24         dataMap = new TreeMap();
 25     }
 26 
 27     public static void main(String[] args) {
 28         ReadWriteLockDemo tester = new ReadWriteLockDemo();
 29 // 第一次获取锁
 30         tester.writeLock.lock();
 31         System.out
 32                 .println(Thread.currentThread().getName() + " get writeLock.");
 33 // 第二次获取锁，应为是可重入锁
 34         tester.writeLock.lock();
 35         System.out
 36                 .println(Thread.currentThread().getName() + " get writeLock.");
 37         tester.readLock.lock();
 38         System.out.println(Thread.currentThread().getName() + " get readLock");
 39         tester.readLock.lock();
 40         System.out.println(Thread.currentThread().getName() + " get readLock");
 41         tester.readLock.unlock();
 42         tester.readLock.unlock();
 43         tester.writeLock.unlock();
 44         tester.writeLock.unlock();
 45         tester.test();
 46     }
 47 
 48     public void test() {
 49 // 读线程比写线程多
 50         for (int i = 0; i < 10; i++) {
 51             new Thread(new reader(this)).start();
 52         }
 53         for (int i = 0; i < 3; i++) {
 54             new Thread(new writer(this)).start();
 55         }
 56     }
 57 
 58     public void read() {
 59 // 获取锁
 60         readLock.lock();
 61         try {
 62             if (dataMap.isEmpty()) {
 63                 Calendar now = Calendar.getInstance();
 64                 System.out.println(now.getTime().getTime() + " R "
 65                         + Thread.currentThread().getName()
 66                         + " get key, but map is empty.");
 67             }
 68             String value = dataMap.get(index);
 69             Calendar now = Calendar.getInstance();
 70             System.out.println(now.getTime().getTime() + " R "
 71                     + Thread.currentThread().getName() + " key = " + index
 72                     + " value = " + value + " map size = " + dataMap.size());
 73             if (value != null) {
 74                 index++;
 75             }
 76         } finally {
 77 // 释放锁
 78             readLock.unlock();
 79         }
 80         try {
 81             Thread.sleep(3000);
 82         } catch (Exception e) {
 83 
 84         }
 85     }
 86 
 87     public void write() {
 88         writeLock.lock();
 89         try {
 90             String value = "value" + key;
 91             dataMap.put(new Integer(key), value);
 92             Calendar now = Calendar.getInstance();
 93             System.out.println(now.getTime().getTime() + " W "
 94                     + Thread.currentThread().getName() + " key = " + key
 95                     + " value = " + value + " map size = " + dataMap.size());
 96             key++;
 97             try {
 98                 Thread.sleep(500);
 99             } catch (InterruptedException e) {
100                 e.printStackTrace();
101             }
102         } finally {
103             writeLock.unlock();
104         }
105     }
106 }
107 
108 class reader implements Runnable {
109     private ReadWriteLockDemo tester = null;
110 
111     public reader(ReadWriteLockDemo tester) {
112         this.tester = tester;
113     }
114 
115     @Override
116     public void run() {
117         Calendar now = Calendar.getInstance();
118         System.out.println(now.getTime().getTime() + " R "
119                 + Thread.currentThread().getName() + " started");
120         for (int i = 0; i < 10; i++) {
121             tester.read();
122         }
123     }
124 }
125 
126 class writer implements Runnable {
127     private ReadWriteLockDemo tester = null;
128 
129     public writer(ReadWriteLockDemo tester) {
130         this.tester = tester;
131     }
132 
133     @Override
134     public void run() {
135         Calendar now = Calendar.getInstance();
136         System.out.println(now.getTime().getTime() + " W "
137                 + Thread.currentThread().getName() + " started");
138         for (int i = 0; i < 10; i++) {
139             tester.write();
140         }
141     }
142 }

 

转载于:https://www.cnblogs.com/haoerlv/p/8494379.html