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


This document describes MCE::Signal version 1.874


 ## 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 | ./mce_script.pl | head -10

                     This works fine without the -setpgrp option:

                        ./mce_script.pl < 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>