python线程问题

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python线程的又一细节


　　首先，在python的线程中，任何在run函数中调用的代码，都是运行在新线程中。
　　其他的实例方法，全部运行在主线程中。
　　上代码：





1 #!/usr/bin/python
2 # -- coding: utf-8 --
3
4 import threading
5 import signal
6 import time
7
8 # 注意：run函数中执行的代码都是在新线程中
9 # 而hander方法在主线程中，可以查看它们的thread id
10
11 def thread_sig():
12     # 在子线程中发送信号
13     signal.alarm(3)
14
15 class ihander(threading.Thread):
16     def __init__(self):
17         super(ihander, self).__init__()
18         print threading.currentThread(), " in __init__"
19         signal.signal(signal.SIGALRM, self.handler)
20     
21     def run(self):
22         print threading.currentThread(), " in run"
23         time.sleep(10)
24     
25     def handler(self, signum, frame):
26         print threading.currentThread(), " in handler"
27         print 'signal: ', signum
28
29 h = ihander()
30 h.start()
31
32 t = threading.Thread(target=thread_sig, args=())
33 t.start()

　　执行结果：



  in __init__
  in run
  in handler
signal:  14
　　
　　我们如果把signal.signal放在其他线程中，就会出错：





1 def thread_sig():
2     # 在子线程中发送信号
3     signal.alarm(3)
4     signal.signal(signal.SIGALRM, h.handler)
5
6 class ihander(threading.Thread):
7     def __init__(self):
8         super(ihander, self).__init__()
9         print threading.currentThread(), " in __init__"
10     
11     def run(self):
12         print threading.currentThread(), " in run"
13         time.sleep(10)
14     
15     def handler(self, signum, frame):
16         print threading.currentThread(), " in handler"
17         print 'signal: ', signum

　　执行结果是：





Exception in thread Thread-2:
Traceback (most recent call last):
File "/usr/lib/python2.7/threading.py", line 551, in __bootstrap_inner
self.run()
File "/usr/lib/python2.7/threading.py", line 504, in run
self.__target(*self.__args, **self.__kwargs)
File "/data/tornado_analyst/test_signal.py", line 14, in thread_sig
signal.signal(signal.SIGALRM, h.handler)
ValueError: signal only works in main thread

　　python报告说，signal只能工作在主线程中。
　　
　　下面是一些关于python中信号的注意点：





/*
NOTES ON THE INTERACTION BETWEEN SIGNALS AND THREADS
When threads are supported, we want the following semantics:
- only the main thread can set a signal handler
- any thread can get a signal handler
- signals are only delivered to the main thread
I.e. we don't support "synchronous signals" like SIGFPE (catching
this doesn't make much sense in Python anyway) nor do we support
signals as a means of inter-thread communication, since not all
thread implementations support that (at least our thread library
doesn't).
We still have the problem that in some implementations signals
generated by the keyboard (e.g. SIGINT) are delivered to all
threads (e.g. SGI), while in others (e.g. Solaris) such signals are
delivered to one random thread (an intermediate possibility would
be to deliver it to the main thread -- POSIX?).  For now, we have
a working implementation that works in all three cases -- the
handler ignores signals if getpid() isn't the same as in the main
thread.  XXX This is a hack.
GNU pth is a user-space threading library, and as such, all threads
run within the same process. In this case, if the currently running
thread is not the main_thread, send the signal to the main_thread.
*/



分类: Python