今天默写售票程序,不加锁时多条线程都执行了,
但当我加上锁后,每次执行都只是其中一条执行,部分运行结果如下 :
Thread-0......ticket.....420
Thread-0......ticket.....419
Thread-0......ticket.....418
Thread-0......ticket.....417
Thread-0......ticket.....416
Thread-0......ticket.....415
Thread-0......ticket.....414
Thread-0......ticket.....413
Thread-0......ticket.....412
Thread-0......ticket.....411
Thread-0......ticket.....410
Thread-0......ticket.....409
Thread-0......ticket.....408
Thread-0......ticket.....407
Thread-0......ticket.....406

我的代码如下,为什么只有一条线程执行?脑子进死胡同了,百思不得其解,求解答............

1. class Ticket implements Runnable
   
2. {
   
3.         private int num=500;
   
4.         private Object obj=new Object();
   
5.         public  void run()
   
6.         {
   
7.                
   
8.                 while(true)
   
9.                 {
   
10.                         synchronized(obj)
    
11.                         {
    
12.                                 show();
    
13.                         }
    
14.                 }
    
15. 
    
16.         }               
    
17.         public void show()
    
18.                 {
    
19.                                 if(num>0)
    
20.                                         {
    
21.                                                 try{Thread.sleep(100);}catch(InterruptedException e){}
    
22.                                                 System.out.println(Thread.currentThread().getName()+"......ticket....."+num--);
    
23.                                         }
    
24.                 }
    
25. }
    
26. 
    
27. class TicketDemo5
    
28. {
    
29.         public static void main(String[] args)
    
30.         {
    
31.                 Ticket t=new Ticket();
    
32.                 Thread t1=new Thread(t);
    
33.                 Thread t2=new Thread(t);
    
34.                 Thread t3=new Thread(t);
    
35.                 Thread t4=new Thread(t);
    
36.                 t1.start();
    
37.                 t2.start();
    
38.                 t3.start();
    
39.                 t4.start();
    
40.         }
    
41. }

复制代码

运行没问题啊
Thread-0......ticket.....500
Thread-0......ticket.....499
Thread-3......ticket.....498
Thread-2......ticket.....497
Thread-2......ticket.....496
Thread-2......ticket.....495
Thread-2......ticket.....494
Thread-2......ticket.....493
Thread-2......ticket.....492
Thread-2......ticket.....491
Thread-1......ticket.....490
Thread-2......ticket.....489
Thread-2......ticket.....488
Thread-2......ticket.....487
Thread-2......ticket.....486
Thread-2......ticket.....485
Thread-3......ticket.....484
Thread-0......ticket.....483
Thread-0......ticket.....482
Thread-3......ticket.....481
Thread-3......ticket.....480
Thread-2......ticket.....479

我运行了一下你的代码！这是我的运行结果，请查收

Thread-2......ticket.....100
Thread-3......ticket.....99
Thread-0......ticket.....98
Thread-0......ticket.....97
Thread-3......ticket.....96
Thread-3......ticket.....95
Thread-3......ticket.....94
Thread-2......ticket.....93
Thread-2......ticket.....92
Thread-1......ticket.....91
Thread-1......ticket.....90
Thread-2......ticket.....89
Thread-2......ticket.....88
Thread-2......ticket.....87
Thread-2......ticket.....86
Thread-2......ticket.....85
Thread-2......ticket.....84
Thread-3......ticket.....83
Thread-3......ticket.....82
Thread-0......ticket.....81
Thread-0......ticket.....80
Thread-0......ticket.....79
Thread-0......ticket.....78
Thread-3......ticket.....77
Thread-3......ticket.....76
Thread-3......ticket.....75
Thread-3......ticket.....74
Thread-2......ticket.....73
Thread-1......ticket.....72
Thread-1......ticket.....71
Thread-1......ticket.....70
Thread-1......ticket.....69
Thread-2......ticket.....68
Thread-3......ticket.....67
Thread-0......ticket.....66
Thread-0......ticket.....65
Thread-3......ticket.....64
Thread-2......ticket.....63
Thread-2......ticket.....62
Thread-2......ticket.....61
Thread-2......ticket.....60
Thread-2......ticket.....59
Thread-1......ticket.....58
Thread-2......ticket.....57
Thread-2......ticket.....56
Thread-2......ticket.....55
Thread-2......ticket.....54
Thread-2......ticket.....53
Thread-2......ticket.....52
Thread-2......ticket.....51
Thread-3......ticket.....50
Thread-3......ticket.....49
Thread-0......ticket.....48
Thread-0......ticket.....47
Thread-0......ticket.....46
Thread-3......ticket.....45
Thread-3......ticket.....44
Thread-2......ticket.....43
Thread-2......ticket.....42
Thread-1......ticket.....41
Thread-2......ticket.....40
Thread-2......ticket.....39
Thread-2......ticket.....38
Thread-2......ticket.....37
Thread-2......ticket.....36
Thread-2......ticket.....35
Thread-3......ticket.....34
Thread-3......ticket.....33
Thread-3......ticket.....32
Thread-3......ticket.....31
Thread-3......ticket.....30
Thread-0......ticket.....29
Thread-3......ticket.....28
Thread-2......ticket.....27
Thread-2......ticket.....26
Thread-2......ticket.....25
Thread-2......ticket.....24
Thread-2......ticket.....23
Thread-2......ticket.....22
Thread-2......ticket.....21
Thread-1......ticket.....20
Thread-1......ticket.....19
Thread-2......ticket.....18
Thread-2......ticket.....17
Thread-3......ticket.....16
Thread-3......ticket.....15
Thread-0......ticket.....14
Thread-0......ticket.....13
Thread-0......ticket.....12
Thread-0......ticket.....11
Thread-3......ticket.....10
Thread-3......ticket.....9
Thread-3......ticket.....8
Thread-3......ticket.....7
Thread-2......ticket.....6
Thread-2......ticket.....5
Thread-2......ticket.....4
Thread-2......ticket.....3
Thread-2......ticket.....2
Thread-2......ticket.....1

没有任何的问题，估计是你的电脑CPU的问题，你多运行几次应该就可以看到其他线程了

梁志冰 发表于 2012-9-25 19:33
没有任何的问题，估计是你的电脑CPU的问题，你多运行几次应该就可以看到其他线程了 ...

class Ticket implements Runnable
{
private int num = 500;
private Object obj = new Object();
public void run()
{
  while(true)
  {
   synchronized(obj
   {
    if(num>0)
    {
     try{Thread.sleep(10);}catch(InterruptedException e){}
     System.out.println(Thread.currentThread().getName()+"......ticket....."+num--);
    }
   }
  }
}
}
class TicketDemo5
{
public static void main(String[] args)
{
  Ticket t = new Ticket();
  Thread t1 = new Thread(t);
  Thread t2 = new Thread(t);
  Thread t3 = new Thread(t);
  Thread t4 = new Thread(t);
  t1.start();
  t2.start();
  t3.start();
  t4.start();
}
}

那你把show()方法的代码直接放到同步中试试

sleep(100),卖10万张火车票.第800多张票看到其它线程执行.
Thread-0......ticket.....99249
Thread-0......ticket.....99248
Thread-0......ticket.....99247
Thread-0......ticket.....99246
Thread-0......ticket.....99245
Thread-0......ticket.....99244
Thread-0......ticket.....99243
Thread-0......ticket.....99242
Thread-0......ticket.....99241
Thread-0......ticket.....99240
Thread-0......ticket.....99239
Thread-0......ticket.....99238
Thread-0......ticket.....99237
Thread-0......ticket.....99236
Thread-0......ticket.....99235
Thread-0......ticket.....99234
Thread-0......ticket.....99233
Thread-0......ticket.....99232
Thread-0......ticket.....99231
Thread-0......ticket.....99230
Thread-0......ticket.....99229
Thread-0......ticket.....99228
Thread-0......ticket.....99227
Thread-0......ticket.....99226
Thread-0......ticket.....99225
Thread-0......ticket.....99224
Thread-0......ticket.....99223
Thread-0......ticket.....99222
Thread-0......ticket.....99221
Thread-0......ticket.....99220
Thread-0......ticket.....99219
Thread-0......ticket.....99218
Thread-0......ticket.....99217
Thread-0......ticket.....99216
Thread-0......ticket.....99215
Thread-0......ticket.....99214
Thread-0......ticket.....99213
Thread-0......ticket.....99212
Thread-0......ticket.....99211
Thread-3......ticket.....99210
Thread-3......ticket.....99209
Thread-3......ticket.....99208
Thread-3......ticket.....99207