NAME

Paranoid::Process - Process Management Functions

MODULE VERSION

$Id: Process.pm,v 0.8 2008/08/28 06:22:51 acorliss Exp $

SYNOPSIS

use Paranoid::Process;

MAXCHILDREN = 100;

$SIG{CHLD} = \&sigchld;
$count = childrenCount();
installChldHandler($sub);
$rv = pfork();

$uid = ptranslateUser("foo");
$gid = ptranslateGroup("foo");
$rv = switchUser($user, $group);

$rv = pcapture($cmd, \$crv, \$out);

REQUIREMENTS

o

Paranoid

o

Paranoid::Debug

o

POSIX

DESCRIPTION

This module provides a few functions meant to make life easier when managing processes. The following export targets are provided:

all               All functions within this module
pfork             All child management functions

Only the function switchUser is currently exported by default.

VARIABLES

MAXCHILDREN

Setting this variable sets a limit to how many children will be forked at a time by pfork. The default is zero, which allows unlimited children. Once the limit is met pfork becomes a blocking call until a child exits so the new one can be spawned.

FUNCTIONS

childrenCount

$count = childrenCount();

This function returns the current number of children spawned by pfork.

installChldHandler

installChldHandler($sub);

This function takes a reference to a subroutine. If used the subroutine will be called every time a child exits. That subroutine will be called with the child's PID and exit value as arguments.

sigchld

$SIG{CHLD} = \&sigchld;

This function decrements the child counter necessary for pfork's operation, as well as calling the user's signal handler with each child's PID and exit value.

pfork

$rv = pfork();

This function should be used in lieu of Perl's fork if you want to take advantage of a blocking fork call that respects the MAXCHILDREN limit. Use of this function, however, also assumes the use of sigchld as the signal handler for SIGCHLD.

ptranslateUser

$uid = ptranslateUser("foo");

This function takes a username and returns the corresponding UID as returned by getpwent. If no match is found it returns undef.

ptranslateGroup

$gid = ptranslateGroup("foo");

This function takes a group name and returns the corresponding GID as returned by getgrent. If no match is found it returns undef.

ptranslateGroup

switchUser

$rv = switchUser($user, $group);

This function can be fed one or two arguments, both either named user or group, or UID or GID. The group argument is optional, but you can pass undef as the user to only switch the group.

pcapture

$rv = pcapture($cmd, \$crv, \$out);

This function executes the passed shell command and returns one of the following three values:

RV    Description
=======================================================
-1    Command failed to execute or died with signal
 0    Command executed but exited with a non-0 RV
 1    Command executed and exited with a 0 RV

The actual return value is populated in the passed scalar reference, while all STDERR/STDOUT output is stored in the last scalar reference. Any errors executing the command will have the error string stored in Paranoid::ERROR.

If the command exited cleanly it will automatically be bit shifted eight bits.

NOTE: Unlike many other functions in this suite it is up to you to detaint the command passed to this function yourself. There's simply no way for me to know ahead of time what kind of convoluted arguments you might be handing this call before system is called. Failing to detaint that argument will cause your script to exit under taint mode.

EXAMPLES

pfork

This following example caps the number of children processes to three at a time:

$SIG{CHLD}  = \&sigchld;
MAXCHILDREN = 3;
for (1 .. 5) {

  # Only the children execute the following block
  unless ($pid = pfork()) {
    # ....
    exit 0;
  }
}

You can also install a child-exit routine to be called by sigchld. For instance, to track the children's history in the parent:

sub recordChild ($$) {
  my ($cpid, $cexit) = @_;

  push(@chistory, [$cpid, $cexit]);
}

installChldHandler(\&recordChild);
for (1 .. 5) {
  unless ($pid = pfork()) {
    # ....
    exit $rv;
  }
}

# Prints the child process history
foreach (@chistory) { print "PID: $$_[0] EXIT: $$_[1]\n" };

HISTORY

None as of yet.

AUTHOR/COPYRIGHT

(c) 2005 Arthur Corliss (corliss@digitalmages.com)

cpanm Paranoid

perl -MCPAN -e shell
install Paranoid