net::server::sig(3)
NAME
Net::Server::SIG - adpf - Safer signal handling
SYNOPSIS
use Net::Server::SIG qw(register_sig check_sigs);
use IO::Select ();
use POSIX qw(WNOHANG);
my $select = IO::Select->new();
register_sig(PIPE => 'IGNORE',
HUP => 'DEFAULT',
USR1 => sub { print "I got a SIG $_[0]0; },
USR2 => sub { print "I got a SIG $_[0]0; },
CHLD => sub { 1 while (waitpid(-1, WNOHANG)
> 0); },
);
### add some handles to the select
$select->add(TDIN);
### loop forever trying to stay alive
while ( 1 ){
### do a timeout to see if any signals got passed us
### while we were processing another signal
my @fh = $select->can_read(10);
my $key;
my $val;
### this is the handler for safe (fine under unsafe
also)
if( &check_sigs() ){
# or my @sigs = &check_sigs();
next unless @fh;
}
my $handle = $fh[@fh];
### do something with the handle
}
DESCRIPTION
Signals in Perl 5 are unsafe. Some future releases may be
able to fix some of this (ie Perl 5.8 or 6.0), but it
would be nice to have some safe, portable signal handling
now. Clarification - much of the time, signals are safe
enough. However, if the program employs forking or
becomes a daemon which can receive many simultaneous sig
nals, then the signal handling of Perl is normally not
sufficient for the task.
Using a property of the select() function,
Net::Server::SIG attempts to fix the unsafe problem. If a
process is blocking on select() any signal will short cir
cuit the select. Using this concept, Net::Server::SIG
does the least work possible (changing one bit from 0 to
1). And depends upon the actual processing of the signals
to take place immediately after the the select call via
the "check_sigs" function. See the example shown above
and also see the sigtest.pl script located in the examples
directory of this distribution.
FUNCTIONS
- "register_sig($SIG => code_ref)"
- Takes key/value pairs where the key is the signal
name, and the argument is either a code ref, or the
words 'DEFAULT' or 'IGNORE'. The function regis
ter_sig must be used in conjuction with check_sigs,
and with a blocking select() function call -- other wise, you will observe the registered signal mysteri
ously vanish. - "unregister_sig($SIG)"
- Takes the name of a signal as an argument. Calls reg
ister_sig with a this signal name and 'DEFAULT' as
arguments (same as register_sig(SIG,'DEFAULT') - "check_sigs()"
- Checks to see if any registered signals have occured.
If so, it will play the registered code ref for that
signal. Return value is array containing any SIGNAL
names that had occured.
AUTHORS
Paul T Seamons (paul@seamons.com)
Rob B Brown (rob@roobik.com) - Provided a sounding board
and feedback in creating Net::Server::SIG and sigtest.pl.
COPYRIGHT
- Copyright (C) 2001, Paul T Seamons
- paul@seamons.com
http://seamons.com/ - This package may be distributed under the terms of ei
- ther the
GNU General Public License - or the
- Perl Artistic License
- All rights reserved.