Propagate system call interruptions in threads

Question

I'm running two python threads (import threading). Both of them are blocked on a open() call; in fact they try to open named pipes in order to write in them, so it's a normal behaviour to block until somebody try to read from the named pipe.

In short, it looks like:

import threading

def f():
    open('pipe2', 'r')

if __name__ == '__main__':
    t = threading.Thread(target=f)
    t.start()
    open('pipe1', 'r')

When I type a ^C, the open() in the main thread is interrupted (raises IOError with errno == 4).

My problem is: the t threads still waits, and I'd like to propagate the interruption behaviour, in order to make it raise IOError too.

What happens if you set daemon=True in the child thread before starting it? — Not_a_Golfer, Apr 11 '12 at 08:59
Nothing more. And, the purpose of my question is not to kill the thread, I'd like him to do some stuff (cleaning) after it receives the signal. — deathiop, Apr 12 '12 at 10:05

Mihai · Answer 1 · 2012-04-11T12:31:35.167

I found this in python docs:
" ... only the main thread can set a new signal handler, and the main thread will be the only one to receive signals (this is enforced by the Python signal module, even if the underlying thread implementation supports sending signals to individual threads). This means that signals can’t be used as a means of inter-thread communication. Use locks instead. "
Maybe you should also check these docs:
exceptions.KeyboardInterrupt

library/signal.html

One other idea is to use select to read the pipe asynchronously in the threads. This works in Linux, not sure about Windows (it's not the cleanest, nor the best implementation):

   #!/usr/bin/python

   import threading
   import os
   import select

   def f():
           f = os.fdopen(os.open('pipe2', os.O_RDONLY|os.O_NONBLOCK))
           finput = [ f ]
           foutput = []
           # here the pipe is scanned and whatever gets in will be printed out
           # ...as long as 'getout' is False
           while finput and not getout:
                   fread, fwrite, fexcep = select.select(finput, foutput, finput)
                   for q in fread:
                           if q in finput:
                                   s = q.read()
                                   if len(s) > 0:
                                           print s

   if __name__ == '__main__':
           getout = False
           t = threading.Thread(target=f)
           t.start()
           try:
                   open('pipe1', 'r')
           except:
                   getout = True

Propagate system call interruptions in threads

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