trylock方法

最新推荐文章于 2025-07-16 10:09:26 发布

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最新推荐文章于 2025-07-16 10:09:26 发布

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文章标签： java

原文链接：http://www.cnblogs.com/chinaifae/p/10193929.html

本文通过实例对比了Java中synchronized关键字与Lock接口的tryLock方法在并发控制上的不同。synchronized会持续尝试获取锁直至成功，而tryLock则在指定时间内尝试获取锁，超时未获取则放弃。文章详细展示了两个线程尝试获取同一把锁的场景，揭示了两种同步机制的行为差异。

synchronized 是不占用到手不罢休的，会一直试图占用下去。

与 synchronized 的钻牛角尖不一样，Lock接口还提供了一个trylock方法。
trylock会在指定时间范围内试图占用，占成功了，就啪啪啪。如果时间到了，还占用不成功，扭头就走~

注意：因为使用trylock有可能成功，有可能失败，所以后面unlock释放锁的时候，需要判断是否占用成功了，如果没占用成功也unlock,就会抛出异常

package multiplethread;
 
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
 
public class TestThread {
 
    public static String now() {
        return new SimpleDateFormat("HH:mm:ss").format(new Date());
    }
 
    public static void log(String msg) {
        System.out.printf("%s %s %s %n", now() , Thread.currentThread().getName() , msg);
    }
 
    public static void main(String[] args) {
        final Lock lock = new ReentrantLock();
 
        Thread t1 = new Thread() {
            public void run() {
                boolean locked = false;
                try {
                    log("线程启动");
                    log("试图占有对象：lock");
 
                    locked = lock.tryLock(1,TimeUnit.SECONDS);
                    if(locked){
                        log("占有对象：lock");
                        log("进行5秒的业务操作");
                        Thread.sleep(5000);
                    }
                    else{
                        log("经过1秒钟的努力，还没有占有对象，放弃占有");
                    }
 
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                     
                    if(locked){
                        log("释放对象：lock");
                        lock.unlock();
                    }
                }
                log("线程结束");
            }
        };
        t1.setName("t1");
        t1.start();
        try {
            //先让t1飞2秒
            Thread.sleep(2000);
        } catch (InterruptedException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }
        Thread t2 = new Thread() {
 
            public void run() {
                boolean locked = false;
                try {
                    log("线程启动");
                    log("试图占有对象：lock");
 
                    locked = lock.tryLock(1,TimeUnit.SECONDS);
                    if(locked){
                        log("占有对象：lock");
                        log("进行5秒的业务操作");
                        Thread.sleep(5000);
                    }
                    else{
                        log("经过1秒钟的努力，还没有占有对象，放弃占有");
                    }
 
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                     
                    if(locked){
                        log("释放对象：lock");
                        lock.unlock();
                    }
                }
                log("线程结束");
            }
        };
        t2.setName("t2");
        t2.start();
    }
 
}