threading.Condition.wait() is not catching SIGTERM

Ned Deily nad at acm.org
Thu Jul 3 22:13:57 CEST 2014


In article <17F05A1B-44C8-4F25-AFE9-5DBCFFB9982B at gmail.com>,
> I have the following code which when executed waits to be interrupted by 
> SIGINT, SIGTERM or SIGQUIT. When an object is initialized, it creates a 
> threading.Condition() and acquires() it! The program then registers the 
> signal handlers where notify() and release() is called when the above 
> mentioned signals are received. After registering the signal handlers, it 
> calls wait() on the condition variable and block.
> 
> When I tried to stop the program with Ctrl-C, its did not respond. IOW, the 
> _signal_handler() method did not get called.  

I'm not sure what you are trying to do but your test case seems flawed.  
threading.Condition is designed to be used with multiple threads but 
your test doesn't actually use threads.  If you run your test with a 
reasonably current Python 3 (after changing print to print()), you can 
see that it fails (and why it fails) when interrupting with Ctrl-C:

Waiting to be interrupted!
^CReceived terminate request - signal = 2
Traceback (most recent call last):
  File "b.py", line 30, in <module>
    main()
  File "b.py", line 27, in main
    a.register_and_wait()
  File "b.py", line 22, in register_and_wait
    self._termination_signal.wait()      # control blocks here!
  File 
"/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/threadin
g.py", line 289, in wait
    waiter.acquire()
  File "b.py", line 13, in _signal_handler
    self._termination_signal.notify()
  File 
"/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/threadin
g.py", line 339, in notify
    raise RuntimeError("cannot notify on un-acquired lock")
RuntimeError: cannot notify on un-acquired lock

After a quick glance, I'm not sure why Python 2.7 is behaving 
differently, e.g. not raising an error, since both versions of 
Condition.notify have the same test so the difference is elsewhere.  
Feel free to open an issue for not catching the error in 2.7 but you 
should rethink what you are trying to do here.

-- 
 Ned Deily,
 nad at acm.org




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