Net::Server::SIG − adpf − Safer signal handling


  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]\n"; },
               USR2 => sub { print "I got a SIG $_[0]\n"; },
               CHLD => sub { 1 while (waitpid(−1, WNOHANG) > 0); },
  ### add some handles to the select
  ### 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


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 signals, 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 circuit 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 script located in the examples directory of this distribution.


"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 register_sig must be used in conjuction with check_sigs, and with a blocking select() function call -- otherwise, you will observe the registered signal mysteriously vanish.


Takes the name of a signal as an argument. Calls register_sig with a this signal name and ’ DEFAULT ’ as arguments (same as register_sig( SIG ,’ DEFAULT ’)


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.


Paul Seamons (

Rob B Brown ( − Provided a sounding board and feedback in creating Net::Server::SIG and


  This package may be distributed under the terms of either the
  GNU General Public License
    or the
  Perl Artistic License
  All rights reserved.


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