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
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
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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(); } } |