MCE::Signal - Temporary directory creation/cleanup and signal handling


This document describes MCE::Signal version 1.875


## Creates tmp_dir under $ENV{TEMP} if defined, otherwise /tmp.

use MCE::Signal;

## Attempts to create tmp_dir under /dev/shm if writable.

use MCE::Signal qw( -use_dev_shm );

## Keeps tmp_dir after the script terminates.

use MCE::Signal qw( -keep_tmp_dir );
use MCE::Signal qw( -use_dev_shm -keep_tmp_dir );

## MCE loads MCE::Signal by default when not present.
## Therefore, load MCE::Signal first for options to take effect.

use MCE::Signal qw( -keep_tmp_dir -use_dev_shm );
use MCE;


This package configures $SIG{ HUP, INT, PIPE, QUIT, and TERM } to point to stop_and_exit and creates a temporary directory. The main process and workers receiving said signals call stop_and_exit, which signals all workers to terminate, removes the temporary directory unless -keep_tmp_dir is specified, and terminates itself.

The location of the temp directory resides under $ENV{TEMP} if defined, otherwise /dev/shm if writeable and -use_dev_shm is specified, or /tmp. On Windows, the temp directory is made under $ENV{TEMP}/Perl-MCE/.

As of MCE 1.405, MCE::Signal no longer calls setpgrp by default. Pass the -setpgrp option to MCE::Signal to call setpgrp.

## Running MCE through Daemon::Control requires setpgrp to be called
## for MCE releases 1.511 and below.

use MCE::Signal qw(-setpgrp);   ## Not necessary for MCE 1.512 and above
use MCE;

The following are available options and their meanings.

-keep_tmp_dir     - The temporary directory is not removed during exiting
                    A message is displayed with the location afterwards

-use_dev_shm      - Create the temporary directory under /dev/shm
-no_kill9         - Do not kill -9 after receiving a signal to terminate

-setpgrp          - Calls setpgrp to set the process group for the process
                    This option ensures all workers terminate when reading
                    STDIN for MCE releases 1.511 and below.

                       cat big_input_file | ./ | head -10

                    This works fine without the -setpgrp option:

                       ./ < big_input_file | head -10

Nothing is exported by default. Exportable are 1 variable and 2 subroutines.

use MCE::Signal qw( $tmp_dir stop_and_exit sys_cmd );
use MCE::Signal qw( :all );

$tmp_dir          - Path to the temporary directory.
stop_and_exit     - Described below
sys_cmd           - Described below

stop_and_exit ( [ $exit_status | $signal ] )

Stops execution, removes temp directory, and exits the entire application. Pass 'INT' to terminate a spawned or running MCE session.


sys_cmd ( $command )

The system function in Perl ignores SIGINT and SIGQUIT. These 2 signals are sent to the command being executed via system() but not back to the underlying Perl script. For this reason, sys_cmd was added to MCE::Signal.

## Execute command and return the actual exit status. The perl script
## is also signaled if command caught SIGINT or SIGQUIT.

use MCE::Signal qw(sys_cmd);   ## Include before MCE
use MCE;

my $exit_status = sys_cmd($command);


defer ( $signal )

Returns immediately inside a signal handler if signaled during IPC. The signal is deferred momentarily and re-signaled automatically upon completing IPC. Currently, all IPC related methods in MCE::Shared and one method send2 in MCE::Channel set the flag $MCE::Signal::IPC before initiating IPC.

Current API available since 1.863.

sub sig_handler {
   return MCE::Signal::defer($_[0]) if $MCE::Signal::IPC;

In a nutshell, defer helps safeguard IPC from stalling between workers and the shared manager-process. The following is a demonstration for Unix platforms. Deferring the signal inside the WINCH handler prevents the app from eventually failing while resizing the window.

use strict;
use warnings;

use MCE::Hobo;
use MCE::Shared;
use Time::HiRes 'sleep';

my $count = MCE::Shared->scalar(0);
my $winch = MCE::Shared->scalar(0);
my $done  = MCE::Shared->scalar(0);

$SIG{WINCH} = sub {
   # defer signal if signaled during IPC
   return MCE::Signal::defer($_[0]) if $MCE::Signal::IPC;

   # mask signal handler
   local $SIG{$_[0]} = 'IGNORE';

   printf "inside winch handler %d\n", $winch->incr;

$SIG{INT} = sub {
   # defer signal if signaled during IPC
   return MCE::Signal::defer($_[0]) if $MCE::Signal::IPC;

   # set flag for workers to leave loop

sub task {
   while ( ! $done->get ) {
      sleep 0.03;

print "Resize the terminal window continuously.\n";
print "Press Ctrl-C to stop.\n";

MCE::Hobo->create('task') for 1..8;
sleep 0.015 until $done->get;

printf "\ncount incremented %d times\n\n", $count->get;


MCE, MCE::Core


Mario E. Roy, <marioeroy AT gmail DOT com>