using filedescriptors in SIGINT signal handler

[Bram Stolk]

Hello,

I catch SIGINT signals with a handler.
In the handler, I use fd's to write some data to a child process.

Is this valid?
Because the data never arrives, and I wonder what I'm doing wrong.

Can filedescriptors still be used when you're in the signal
handling of SIGINT?

Thanks,

Bram

[jepler@unpythonic.net]

Re: using filedescriptors in SIGINT signal handler

If you're talking about a Python function registered as a handler by
signal.signal, then there should not be any restrictions on what you do
in that function.

Here's a small program I wrote:
#------------------------------------------------------------------------
import os, signal, time

def h(*args): os.write(fd, "data\n");

print "my pid is", os.getpid()
subproc = os.popen("cat -n", "w")
fd = subproc.fileno( )

signal.signal(s ignal.SIGINT, h)

while 1:
time.sleep(1)
#------------------------------------------------------------------------

I ran this and in another terminal I repeatedly typed 'kill -INT nnnn',
where nnnn is the pid printed by my program. Each time, another line is
output by 'cat'.

When I try to deliver the signal by hitting ctrl-c in that terminal, the
first time nothing happens and the second time I get the message
OSError: [Errno 32] Broken pipe
in this case, I believe that the first signal was delivered to cat,
causing it to exit. The second signal was delivered to the python
program, which obviously couldn't write to the stdin of a process that
had exited.

Jeff

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[Bram Stolk]

Re: using filedescriptors in SIGINT signal handler

jepler@unpython ic.net wrote:[color=blue]
> If you're talking about a Python function registered as a handler by
> signal.signal, then there should not be any restrictions on what you do
> in that function.
>
> Here's a small program I wrote:
> #------------------------------------------------------------------------
> import os, signal, time
>
> def h(*args): os.write(fd, "data\n");
>
> print "my pid is", os.getpid()
> subproc = os.popen("cat -n", "w")
> fd = subproc.fileno( )
>
> signal.signal(s ignal.SIGINT, h)
>
> while 1:
> time.sleep(1)
> #------------------------------------------------------------------------
>
> I ran this and in another terminal I repeatedly typed 'kill -INT nnnn',
> where nnnn is the pid printed by my program. Each time, another line is
> output by 'cat'.
>
> When I try to deliver the signal by hitting ctrl-c in that terminal, the
> first time nothing happens and the second time I get the message
> OSError: [Errno 32] Broken pipe
> in this case, I believe that the first signal was delivered to cat,
> causing it to exit. The second signal was delivered to the python
> program, which obviously couldn't write to the stdin of a process that
> had exited.[/color]

Ah!
ofcourse...

It makes sense now to me.
I, indeed, used Ctrl-C, and assumed it would go to python, not
the child process. Wrong assumption ofcourse.

Thanks.

Bram
[color=blue]
>
> Jeff[/color]