多线程例子:wait与notify、sleep
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- 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。
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