trylock方法

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();
    }

}

转载于:https://www.cnblogs.com/chinaifae/p/10193929.html