ReentrantLock使用详解(3)之测试锁与超时

我在上面的这篇博客中，曾经写到过线程在获取锁的过程中是无法中断的。

但是ReentrantLock提供了tryLock()、tryLock(long timeout, TimeUnit unit)、lock.lockInterruptibly()

tryLock() 方法试图申请一个锁，在成功获得锁后返回true，否则，立即返回false,而且线程可以立即离开去做其他的事情。

tryLock(long timeout, TimeUnit unit) 是一个具有超时参数的尝试申请锁的方法，阻塞时间不会超过给定的值；如果成功则返回true

lockInterruptibly() 获得锁，但是会不确定地发生阻塞。如果线程被中断，抛出一个InterruptedException异常。

如果当前获得锁的线程在做大量耗时的工作，使用lock.lock()方法申请锁的线程会一直阻塞，这样就降低了多线程的效率。而使用tryLock()方法申请锁，如果锁不可用则线程不会阻塞，转而可以去做其他工作。代码实例如下：

[java] view plain copy print?

1. public class ReentrantLockTest4 {  
2.   
3.     private ReentrantLock lock = new ReentrantLock();  
4.       
5.     public void tryLockTest() throws InterruptedException {  
6.           
7.         long beginTime = System.currentTimeMillis();  
8.         while(System.currentTimeMillis() - beginTime <100) {}  
9.         // 当前线程尝试获得锁，如果获得锁返回true，否则返回false  
10.         if(lock.tryLock()) {  
11.             try{  
12.                 System.out.println(Thread.currentThread().getName() + " tryLock get lock");  
13.             } finally {  
14.                 lock.unlock();  
15.                 System.out.println(Thread.currentThread().getName() + " tryLock release lock");  
16.             }  
17.         } else {  
18.             System.out.println(Thread.currentThread().getName() + " tryLock can not get lock");  
19.         }  
20.           
21.     }  
22.       
23.       
24.     public void lockTest() {  
25.         try{  
26.             // 当前线程在锁可用时直接获得锁，锁不可用时阻塞当前线程  
27.             lock.lock();  
28.             System.out.println(Thread.currentThread().getName() + " lock get lock");  
29.             long beginTime = System.currentTimeMillis();  
30.             while(System.currentTimeMillis() - beginTime <1000) {}  
31.         } finally {  
32.             lock.unlock();  
33.             System.out.println(Thread.currentThread().getName() + " lock release lock");  
34.         }  
35.   
36.     }  
37.       
38.     public static void main(String[] args) {  
39.         // TODO Auto-generated method stub  
40.         final ReentrantLockTest4 test = new ReentrantLockTest4();  
41.         Thread tryLock = new Thread(new Runnable() {  
42.             public void run() {  
43.                 try {  
44.                     test.tryLockTest();  
45.                 } catch (InterruptedException e) {  
46.                     // TODO Auto-generated catch block  
47.                     e.printStackTrace();  
48.                 }  
49.             }  
50.         },"tryLock_thread");  
51.           
52.         Thread lock = new Thread(new Runnable() {  
53.             public void run() {  
54.                 test.lockTest();  
55.             }  
56.         },"lock_thread");  
57.           
58.         tryLock.start();  
59.         lock.start();  
60.     }  
61.   
62. }  
63.   
64. 输出结果：  
65. lock_thread lock get lock  
66. tryLock_thread tryLock can not get lock  
67. lock_thread lock release lock  

public class ReentrantLockTest4 {private ReentrantLock lock = new ReentrantLock();public void tryLockTest() throws InterruptedException {long beginTime = System.currentTimeMillis();while(System.currentTimeMillis() - beginTime <100) {}// 当前线程尝试获得锁，如果获得锁返回true，否则返回falseif(lock.tryLock()) {try{System.out.println(Thread.currentThread().getName() + " tryLock get lock");} finally {lock.unlock();System.out.println(Thread.currentThread().getName() + " tryLock release lock");}} else {System.out.println(Thread.currentThread().getName() + " tryLock can not get lock");}}public void lockTest() {try{// 当前线程在锁可用时直接获得锁，锁不可用时阻塞当前线程lock.lock();System.out.println(Thread.currentThread().getName() + " lock get lock");long beginTime = System.currentTimeMillis();while(System.currentTimeMillis() - beginTime <1000) {}} finally {lock.unlock();System.out.println(Thread.currentThread().getName() + " lock release lock");}}public static void main(String[] args) {// TODO Auto-generated method stubfinal ReentrantLockTest4 test = new ReentrantLockTest4();Thread tryLock = new Thread(new Runnable() {public void run() {try {test.tryLockTest();} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}}},"tryLock_thread");Thread lock = new Thread(new Runnable() {public void run() {test.lockTest();}},"lock_thread");tryLock.start();lock.start();}}输出结果：lock_thread lock get locktryLock_thread tryLock can not get locklock_thread lock release lock

lock方法不能被中断。如果一个线程在等待获得一个锁时被中断，中断线程在获得锁之前会一直处于 阻塞状态。如果出现死锁，那么lock方法就无法被终止。但是tryLock和lockInterruptibly方法在申请锁的过程中是可以被中断的。代码如下

[java] view plain copy print?

1. public class ReentrantLockTest5 {  
2.       
3.     private ReentrantLock lock = new ReentrantLock();  
4.       
5.     public void tryLockInterruptTest() {  
6.         long beginTime = System.currentTimeMillis();  
7.         while(System.currentTimeMillis() - beginTime <100) {}  
8.         try {  
9.             if (lock.tryLock(5000, TimeUnit.MILLISECONDS)) {  
10.                 try{  
11.                     System.out.println(Thread.currentThread().getName() + " tryLock get lock");  
12.                 }finally {  
13.                     lock.unlock();  
14.                 }  
15.             }  
16.         } catch (InterruptedException e) {  
17.             // TODO Auto-generated catch block  
18.             System.out.println(Thread.currentThread().getName() + " was interrupted");  
19.         }  
20.     }  
21.       
22.       
23.     public void lockTest() {  
24.         try{  
25.             // 当前线程在锁可用时直接获得锁，锁不可用时阻塞当前线程  
26.             lock.lock();  
27.             System.out.println(Thread.currentThread().getName() + " lock get lock");  
28.             long beginTime = System.currentTimeMillis();  
29.             while(System.currentTimeMillis() - beginTime <1000) {}  
30.         } finally {  
31.             lock.unlock();  
32.             System.out.println(Thread.currentThread().getName() + " lock release lock");  
33.         }  
34.   
35.     }  
36.       
37.     public static void main(String[] args) {  
38.         // TODO Auto-generated method stub  
39.         final ReentrantLockTest5 test =  new ReentrantLockTest5();  
40.         Thread thread_tryLock = new Thread(new Runnable(){  
41.             @Override  
42.             public void run() {  
43.                 // TODO Auto-generated method stub  
44.                 test.tryLockInterruptTest();  
45.             }  
46.         },"tryLockInterruptTest");  
47.         Thread thread_lock = new Thread(new Runnable(){  
48.             @Override  
49.             public void run() {  
50.                 // TODO Auto-generated method stub  
51.                 test.lockTest();  
52.             }  
53.         },"lockTest");  
54.         thread_tryLock.start();  
55.         thread_lock.start();  
56.         try {  
57.             Thread.sleep(200);  
58.         } catch (InterruptedException e) {  
59.             // TODO Auto-generated catch block  
60.             System.out.println("main thread was interrupted");  
61.         }  
62.         thread_tryLock.interrupt();  
63.     }  
64.   
65. }  
66.   
67.   
68. 输出结果：  
69. lockTest lock get lock  
70. tryLockInterruptTest was interrupted  
71. lockTest lock release lock