tryLock(long time, TimeUnit unit) 的作用在给定等待时长内锁没有被另外的线程持有，并且当前线程也没有被中断,则获得该锁，通过该方法可以实现锁对象的限时等待。
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package com.wkcto.lock.reentrant;
import java.util.concurrent.TimeUnit; import java.util.concurrent.locks.ReentrantLock;
/** *tryLock(long time, TimeUnit unit) 的基本使用 */ public class Test07 { static class TimeLock implements Runnable{ private static ReentrantLock lock = new ReentrantLock(); //定义锁对象
@Override public void run() { try { if ( lock.tryLock( 3 , TimeUnit.SECONDS) ){ //获得锁返回true System.out.println(Thread.currentThread().getName() + "获得锁,执行耗时任务" ); // Thread.sleep(4000); //假设Thread-0线程先持有锁,完成任务需要4秒钟,Thread-1线程尝试获得锁,Thread-1线程在3秒内还没有获得锁的话,Thread-1线程会放弃 Thread.sleep( 2000 ); //假设Thread-0线程先持有锁,完成任务需要2秒钟,Thread-1线程尝试获得锁,Thread-1线程会一直尝试,在它约定尝试的3秒内可以获得锁对象 } else { //没有获得锁 System.out.println(Thread.currentThread().getName() + "没有获得锁" ); } } catch (InterruptedException e) { e.printStackTrace(); } finally { if (lock.isHeldByCurrentThread()){ lock.unlock(); } } } }
public static void main(String[] args) { TimeLock timeLock = new TimeLock();
Thread t1 = new Thread(timeLock); Thread t2 = new Thread(timeLock); t1.start(); t2.start(); } } |
tryLock()仅在调用时锁定未被其他线程持有的锁，如果调用方法时，锁对象对其他线程持有，则放弃，调用方法尝试获得没，如果该锁没有被其他线程占用则返回true表示锁定成功; 如果锁被其他线程占用则返回false,不等待。
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package com.wkcto.lock.reentrant;
import java.util.concurrent.locks.ReentrantLock;
/** *tryLock() * 当锁对象没有被其他线程持有的情况下才会获得该锁定 */ public class Test08 { static class Service{ private ReentrantLock lock = new ReentrantLock(); public void serviceMethod(){ try { if (lock.tryLock()){ System.out.println(Thread.currentThread().getName() + "获得锁定" ); Thread.sleep( 3000 ); //模拟执行任务的时长 } else { System.out.println(Thread.currentThread().getName() + "没有获得锁定" ); } } catch (InterruptedException e) { e.printStackTrace(); } finally { if (lock.isHeldByCurrentThread()){ lock.unlock(); } } } }
public static void main(String[] args) throws InterruptedException { Service service = new Service(); Runnable r = new Runnable() { @Override public void run() { service.serviceMethod(); } };
Thread t1 = new Thread(r); t1.start(); Thread.sleep( 50 ); //睡眠50毫秒,确保t1线程锁定 Thread t2 = new Thread(r); t2.start(); } } |
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package com.wkcto.lock.reentrant;
import java.util.Random; import java.util.concurrent.locks.ReentrantLock;
/** * 使用tryLock()可以避免死锁 */ public class Test09 { static class IntLock implements Runnable{ private static ReentrantLock lock1 = new ReentrantLock(); private static ReentrantLock lock2 = new ReentrantLock(); private int lockNum; //用于控制锁的顺序
public IntLock( int lockNum) { this .lockNum = lockNum; }
@Override public void run() { if ( lockNum % 2 == 0 ){ //偶数先锁1,再锁2 while ( true ){ try { if (lock1.tryLock()){ System.out.println(Thread.currentThread().getName() + "获得锁1, 还想获得锁2" ); Thread.sleep( new Random().nextInt( 100 ));
try { if (lock2.tryLock()){ System.out.println(Thread.currentThread().getName() + "同时获得锁1与锁2 ----完成任务了" ); return ; //结束run()方法执行,即当前线程结束 } } finally { if (lock2.isHeldByCurrentThread()){ lock2.unlock(); } } } } catch (InterruptedException e) { e.printStackTrace(); } finally { if (lock1.isHeldByCurrentThread()){ lock1.unlock(); } } } } else { //奇数就先锁2,再锁1 while ( true ){ try { if (lock2.tryLock()){ System.out.println(Thread.currentThread().getName() + "获得锁2, 还想获得锁1" ); Thread.sleep( new Random().nextInt( 100 ));
try { if (lock1.tryLock()){ System.out.println(Thread.currentThread().getName() + "同时获得锁1与锁2 ----完成任务了" ); return ; //结束run()方法执行,即当前线程结束 } } finally { if (lock1.isHeldByCurrentThread()){ lock1.unlock(); } } } } catch (InterruptedException e) { e.printStackTrace(); } finally { if (lock2.isHeldByCurrentThread()){ lock2.unlock(); } } } } } } public static void main(String[] args) { IntLock intLock1 = new IntLock( 11 ); IntLock intLock2 = new IntLock( 22 ); Thread t1 = new Thread(intLock1); Thread t2 = new Thread(intLock2); t1.start(); t2.start(); //运行后,使用tryLock()尝试获得锁,不会傻傻的等待,通过循环不停的再次尝试,如果等待的时间足够长,线程总是会获得想要的资源 } } |
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