[Numpy-discussion] Handling interrupts in NumPy extensions

[David Cournapeau]

Travis Oliphant wrote:
>
> Right, as long as you know what to do you are O.K.  I was just thinking 
> about a hypothetical situation where the library allocated some 
> temporary memory that it was going to free at the end of the subroutine 
> but then an interrupt jumped out back to your code before it could 
> finish.   In a case like this, you would have to use the "check if 
> interrupt has occurred" approach before and after the library call. 
Indeed.

By the way, I tried something for python.thread + signals. This is posix 
specific, and it works as expected on linux:

 - first, a C extension which implements the signal handling. It has a 
function called hello, which is the entry point of the C module, and 
calls the function process (which does random computation). It checks if 
it got a SIGINT signal, and returns -1 if caught. Returns 0 if no SIGINT 
called:
 - extension compiled into python module (I used boost python because I 
am too lazy to find how to do it in C :) )
 - python script which creates several threads running the hello 
function. They run in parallel, and ctrl+C is correctly handled. I think 
this is signal specific, and this needs to be improved (this is just 
meant as a toy example):

import threading
import hello
import time

class mythread(threading.Thread):
    def __init__(self):
        threading.Thread.__init__(self)
    def run(self):
        print "Starting thread", self.getName()
        st  = 0
        while st == 0:
            st  = hello.foo(self.getName())
            # sleep to force the python interpreter to run
            # other threads if available
            time.sleep(1)
            if st == -1:
                print self.getName() + " got signal"
        print "Ending thread", self.getName()

nthread = 5
t   = [mythread() for i in range(nthread)]
[i.start() for i in t]

Then, you have something like:

tarting thread Thread-1
Thread-1 processing... done
clean called
Starting thread Thread-5
Thread-5 processing... done
clean called
Starting thread Thread-3
Thread-3 processing... done
clean called
Starting thread Thread-2
Thread-2 processing... done
hello.c:hello signal caught line 56 for thread Thread-2
clean called
Thread-1 processing... done
clean called
Starting thread Thread-4
Thread-4 processing... done
clean called
Thread-5 processing... done
clean called
Thread-3 processing... done
hello.c:hello signal caught line 56 for thread Thread-3
clean called
Thread-2 got signal
Ending thread Thread-2
Thread-1 processing... done
clean called
Thread-4 processing... done
clean called
Thread-5 processing... done
clean called
Thread-3 got signal
Ending thread Thread-3
Thread-1 processing... done
hello.c:hello signal caught line 56 for thread Thread-1
clean called
Thread-4 processing... done
clean called
Thread-5 processing... done
hello.c:hello signal caught line 56 for thread Thread-5
clean called
Thread-1 got signal
Ending thread Thread-1
Thread-4 processing... done
clean called
Thread-5 got signal
Ending thread Thread-5
Thread-4 processing... done
clean called
Thread-4 processing... done
clean called
Thread-4 processing... done
hello.c:hello signal caught line 56 for thread Thread-4
clean called
Thread-4 got signal
Ending thread Thread-4

(SIGINT are received when Ctrl+C on linux)

You can find all sources here:

http://www.ar.media.kyoto-u.ac.jp/members/david/numpysig/

Please note that I know almost nothing about all this stuff, I just 
naively implemented from the example of GNU C library, and it always 
worked for me on matlab on my machine. I do not know if this is 
portable, if this can work for other signals, etc...

David