Java多线程与并发 --- notify 和 notifyall 的区别

冷不防 2022-02-04 13:41 222阅读 0赞

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3hpbmJ1bWk_size_16_color_FFFFFF_t_70][]

notify 和 notifyall  唤醒锁

notify 和 notifyall  的区别

先明白两个概念：

锁池：EntryList

等待池：WaitSet

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3hpbmJ1bWk_size_16_color_FFFFFF_t_70 1][]

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3hpbmJ1bWk_size_16_color_FFFFFF_t_70 2][] 这个时候 再来看 notify 和 notifyall  的区别：

notifyall ： 会让所有处于等待池的线程全部进入锁池去竞争获取锁的机会

notify ： 只会随机选取一个处于等待池中的线程进入锁池中去竞争获取锁的机会

1.  public class NotificationDemo \{
2.  private volatile boolean go = false;
3.   
4.  public static void main(String args\[\]) throws InterruptedException \{
5.  final NotificationDemo test = new NotificationDemo();
6.   
7.  Runnable waitTask = new Runnable()\{
8.   
9.  @Override
10. public void run()\{
11. try \{
12. test.shouldGo();
13. \} catch (InterruptedException e) \{
14. e.printStackTrace();
15. \}
16. System.out.println(Thread.currentThread().getName() + " finished Execution");
17. \}
18. \};
19.  
20. Runnable notifyTask = new Runnable()\{
21.  
22. @Override
23. public void run()\{
24. test.go();
25. System.out.println(Thread.currentThread().getName() + " finished Execution");
26. \}
27. \};
28.  
29. Thread t1 = new Thread(waitTask, "WT1"); //will wait
30. Thread t2 = new Thread(waitTask, "WT2"); //will wait
31. Thread t3 = new Thread(waitTask, "WT3"); //will wait
32. Thread t4 = new Thread(notifyTask,"NT1"); //will notify
33.  
34. //starting all waiting thread
35. t1.start();
36. t2.start();
37. t3.start();
38.  
39. //pause to ensure all waiting thread started successfully
40. Thread.sleep(200);
41.  
42. //starting notifying thread
43. t4.start();
44.  
45. \}
46. /\*
47. \* wait and notify can only be called from synchronized method or bock
48. \*/
49. private synchronized void shouldGo() throws InterruptedException \{
50. while(go != true)\{
51. System.out.println(Thread.currentThread()
52. \+ " is going to wait on this object");
53. wait(); //release lock and reacquires on wakeup
54. System.out.println(Thread.currentThread() + " is woken up");
55. \}
56. go = false; //resetting condition
57. \}
58.  
59. /\*
60. \* both shouldGo() and go() are locked on current object referenced by "this" keyword
61. \*/
62. private synchronized void go() \{
63. while (go == false)\{
64. System.out.println(Thread.currentThread()
65. \+ " is going to notify all or one thread waiting on this object");
66.  
67. go = true; //making condition true for waiting thread
68. //notify(); // only one out of three waiting thread WT1, WT2,WT3 will woke up
69. notifyAll(); // all waiting thread WT1, WT2,WT3 will woke up
70. \}
71.  
72. \}
73. \}

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