信号处理程序延迟执行

winway1988

1. [winway@s208 test]$ cat test.py
   
2. #! /usr/bin/env python
   
3. # -*- coding: utf-8 -*-
   
4. #
   
5. 
   
6. import signal
   
7. import threading
   
8. import os
   
9. import time
   
10. 
    
11. def signal_handler(num, stack):
    
12.     print num, threading.currentThread().name
    
13. 
    
14. signal.signal(signal.SIGALRM, signal_handler)
    
15. 
    
16. def wait_for_signal():
    
17.     print 'wait_for_signal in', threading.currentThread().name
    
18.     time.sleep(10)
    
19.     print 'leave wait_for_signal'
    
20. 
    
21. receiver = threading.Thread(target=wait_for_signal, name='receiver')
    
22. receiver.start()
    
23. time.sleep(1)
    
24. 
    
25. signal.alarm(2)
    
26. receiver.join()
    
27. [winway@s208 test]$ ./test.py
    
28. wait_for_signal in receiver
    
29. leave wait_for_signal
    
30. 14 MainThread

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我的疑问是，为什么SIGALRM信号在receiver.join()返回后才被处理？

winway1988

1. [winway@s208 test]$ cat test.py
   
2. #! /usr/bin/env python
   
3. # -*- coding: utf-8 -*-
   
4. #
   
5. 
   
6. import signal
   
7. import threading
   
8. import os
   
9. import time
   
10. 
    
11. def signal_handler(num, stack):
    
12.     print num, threading.currentThread().name
    
13. 
    
14. #signal.signal(signal.SIGALRM, signal_handler)
    
15. 
    
16. def wait_for_signal():
    
17.     print 'wait_for_signal in', threading.currentThread().name
    
18.     time.sleep(10)
    
19.     print 'leave wait_for_signal'
    
20. 
    
21. receiver = threading.Thread(target=wait_for_signal, name='receiver')
    
22. receiver.start()
    
23. time.sleep(1)
    
24. 
    
25. signal.alarm(2)
    
26. receiver.join()
    
27. [winway@s208 test]$ ./test.py
    
28. wait_for_signal in receiver
    
29. Alarm clock

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如果不改变sigalrm的处理方式，好像signal.alarm(2)就是立即生效的，即2秒后主线程退出。注册了自己的处理函数，就延迟了