多线程例子：wait与notify、sleep

package sure;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


public class Test {

	private static Logger log = LoggerFactory.getLogger(Test.class);
	
    public static void main(String[] args) throws Exception {  
        final Object lock="";  
        Thread t1=new Thread(){  
            public void run(){  
                try {  
                	log.info("t1 wait begin");  
                    synchronized (lock) {  
                    	log.info("t1 get lock, wait begin");
                        lock.wait();  
                        log.info("t1 wait end,release lock");
                        lock.notifyAll();
                    }  
                    log.info("t1  wait end");  
                } catch (InterruptedException e) {  
                    e.printStackTrace();  
                }  
            }  
        };  
          
        t1.start();  
        log.info("t1 start and sleep");
        for(int i=0;i<10000001;i++){
        	if(i==10000000)
        		log.info("i end");
        }
        Thread.sleep(5000);  
        log.info("sleep(5000) end");
          
        log.info("main lock begin");  
        synchronized (lock) {
        	log.info("main get lock");
            lock.notify();
            log.info("notify");
            Thread.sleep(10000); 
            log.info("sleep 10000 end");
            log.info("main wait begin ");  
            lock.wait();  
            log.info("main wait end");  
        }  
        log.info("main lock end");  
    }  
}

日志信息如下：

2011-11-09 15:44:05,968 INFO [sure.Test] - t1 start and sleep
2011-11-09 15:44:05,968 INFO [sure.Test] - t1 wait begin
2011-11-09 15:44:05,968 INFO [sure.Test] - t1 get lock, wait begin
2011-11-09 15:44:05,984 INFO [sure.Test] - i end
2011-11-09 15:44:10,984 INFO [sure.Test] - sleep(5000) end
2011-11-09 15:44:10,984 INFO [sure.Test] - main lock begin
2011-11-09 15:44:10,984 INFO [sure.Test] - main get lock
2011-11-09 15:44:10,984 INFO [sure.Test] - notify
2011-11-09 15:44:20,984 INFO [sure.Test] - sleep 10000 end
2011-11-09 15:44:20,984 INFO [sure.Test] - main wait begin 
2011-11-09 15:44:20,984 INFO [sure.Test] - t1 wait end,release lock
2011-11-09 15:44:20,984 INFO [sure.Test] - t1  wait end
2011-11-09 15:44:20,984 INFO [sure.Test] - main wait end
2011-11-09 15:44:20,984 INFO [sure.Test] - main lock end

wait，notify，notifyAll必须在当前线程获得监视器时才能调用，即这些方法必须在同步块中才能调用。

被阻塞的线程在被notify之后，并不是马上可以执行，而是“可执行”，要到获得锁之后才能真正开始执行。

从这个例子进行各种修改可以用来加深对线程的理解。

package sure;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


public class Test {

	private static Logger log = LoggerFactory.getLogger(Test.class);
	
    public static void main(String[] args) throws Exception {  
        final Object lock="";  
        Thread t1=new Thread(){  
            public void run(){  
                try {  
                	log.info("t1 wait begin");  
                    synchronized (lock) {  
                    	log.info("t1 get lock, wait begin");
                    	Thread.sleep(5000);
                    	log.info("sleep end");
                        lock.wait();  
                        log.info("t1 wait end,release lock");
                        lock.notifyAll();
                    }  
                    Thread.sleep(5000);
                    log.info("t1  wait end");  
                } catch (InterruptedException e) {  
                    e.printStackTrace();  
                }  
            }  
        };  
          
        t1.start();  
        log.info("t1 start and sleep");
          
        log.info("main lock begin");  
        synchronized (lock) {
        	log.info("main get lock");
            lock.notify();
            log.info("notify");
            Thread.sleep(10000); 
            log.info("sleep 10000 end");
            log.info("main wait begin ");  
            lock.wait();  
            log.info("main wait end");  
        }  
        log.info("main lock end");  
       
    }  

}

日志为：

2011-11-09 16:55:19,031 INFO [sure.Test] - t1 start and sleep
2011-11-09 16:55:19,031 INFO [sure.Test] - main lock begin
2011-11-09 16:55:19,031 INFO [sure.Test] - main get lock
2011-11-09 16:55:19,031 INFO [sure.Test] - notify
2011-11-09 16:55:19,031 INFO [sure.Test] - t1 wait begin
2011-11-09 16:55:29,031 INFO [sure.Test] - sleep 10000 end
2011-11-09 16:55:29,031 INFO [sure.Test] - main wait begin 
2011-11-09 16:55:29,031 INFO [sure.Test] - t1 get lock, wait begin
2011-11-09 16:55:34,031 INFO [sure.Test] - sleep end

然后两个线程都会被阻塞，造成死锁。
这个例子进一步说明了同步的用法，另外也表明了Thread.sleep是针对当前运行线程的。

有趣的是，同样是这个代码，在另一种情况下会出现这种情况：

2011-11-09 22:06:05,930 INFO [sure.Test] - t1 start and sleep
2011-11-09 22:06:05,930 INFO [sure.Test] - t1 wait begin
2011-11-09 22:06:05,930 INFO [sure.Test] - main lock begin
2011-11-09 22:06:05,930 INFO [sure.Test] - t1 get lock, wait begin
2011-11-09 22:06:10,930 INFO [sure.Test] - sleep end
2011-11-09 22:06:10,930 INFO [sure.Test] - main get lock
2011-11-09 22:06:10,930 INFO [sure.Test] - notify
2011-11-09 22:06:20,930 INFO [sure.Test] - sleep 10000 end
2011-11-09 22:06:20,930 INFO [sure.Test] - main wait begin 
2011-11-09 22:06:20,930 INFO [sure.Test] - t1 wait end,release lock
2011-11-09 22:06:20,930 INFO [sure.Test] - main wait end
2011-11-09 22:06:20,930 INFO [sure.Test] - main lock end
2011-11-09 22:06:25,930 INFO [sure.Test] - t1  wait end

这种情况不会造成死锁阻塞。
由于这两个线程都谁都可能先进入同步块中，所以就造成了两个截然不同的情况。但是上面第一种情况就肯定是子进程先进入同步块，因为main进程用sleep拖延了。