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Re^4: TSHARK Child: Windows open2 non-blocking read, or redesign?

by afoken (Chancellor)
on Oct 13, 2010 at 08:59 UTC ( [id://865049]=note: print w/replies, xml ) Need Help??


in reply to Re^3: TSHARK Child: Windows open2 non-blocking read, or redesign?
in thread TSHARK Child: Windows open2 non-blocking read, or redesign?

kill works for processes outside of Perl as well on Win32.

... for a very limited definition of "works". You can use kill to terminate other processes, but you can't send them signals, because Windows doesn't implement signals.

Inside a perl.exe process that pseudo-fork()ed a child-pseudo-process, signals may work, but not outside that process.

Simple example:

killme.pl

#!perl use strict; use warnings; $SIG{'HUP'}=sub { print "Got a HUP signal\n"; }; $SIG{'TERM'}=sub { print "Got a TERM signal\n"; }; open my $f,'>','pid.txt' or die "Could not write pid.txt: $!"; print $f "$$\n"; close $f; $|=1; print "Waiting to be killed\n"; while (1) { print '.'; sleep 30; }

killer.pl:

#!perl use warnings; use strict; open my $f,'<','pid.txt' or die "Start killme.pl first"; my $pid=<$f>; close $f; for my $sig (qw( HUP TERM KILL )) { print "Sending $sig ...\n"; kill($sig,$pid); sleep 2; }

Open two terminals on a Linux system, start both scripts (killme.pl first), and you see this:

tty1tty2
/home/foken>perl killme.pl Waiting to be killed .Got a HUP signal .Got a TERM signal .Killed /home/foken>
/home/foken>perl killer.pl Sending HUP ... Sending TERM ... Sending KILL ... /home/foken>

Open two command shells on Windows, start both scripts (again killme.pl first) and you see this:

Shell 1Shell 2
F:\>perl killme.pl Waiting to be killed . F:\>
F:\>perl killer.pl Sending HUP ... Sending TERM ... Sending KILL ... F:\>

Note that sending HUP terminated killme.pl, completely ignoring the fact that it has set up a HUP signal handler.

One could argue that Windows has no HUP signal, so let's remove the relevant code parts and watch again:

Shell 1Shell 2
F:\>perl killme.pl Waiting to be killed . F:\>
F:\>perl killer.pl Sending TERM ... Sending KILL ... F:\>

Ooops, death by SIGTERM, again ignoring the signal handler inside killme.pl.

Alexander

--
Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)

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Re^5: TSHARK Child: Windows open2 non-blocking read, or redesign?
by Corion (Patriarch) on Oct 13, 2010 at 09:03 UTC

    Ah yes - I avoid signals, because as you said, they don't work on Windows. I only use kill to terminate processes, so for that (admittedly very) limited view of things, it works for me.

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