trusty (3) Paranoid::Process.3pm.gz
NAME
Paranoid::Process - Process Management Functions
VERSION
$Id: Process.pm,v 1.01 2010/05/10 04:55:07 acorliss Exp $
SYNOPSIS
use Paranoid::Process;
$rv = daemonize();
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);
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 functions switchUser and daemonize are currently exported by default.
SUBROUTINES/METHODS
MAXCHILDREN
Setting this lvalue subroutine 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.
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.
daemonize
$rv = daemonize();
This function forks a child who reopens all STD* filehandles on /dev/null and starts a new process group.
The parent exits cleanly. If the fork fails for any reason it returns a false value. The child will
also change its directory to /.
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.
switchUser
$rv = switchUser($user, $group);
This function can be fed one or two arguments, both either named user or group, or UID or GID. Both user
and group arguments are optional as long as the other is called. In other words, you can pass undef for
one of the arguments, but not for both. If you're only switching the user you can pass only the user
argument.
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.
DEPENDENCIES
o Paranoid
o Paranoid::Debug
o POSIX
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" };
BUGS AND LIMITATIONS
There's a bug in an current versions of Perl where ptranslateGroup can return negative numbers instead
the actual GID. This is due to the platform supporting unsigned integers for the GID, but Perl was
casting it as a signed integer. A patch has been submitted to blead-perl.
On Solaris pcapture doesn't return a -1 for non-existant commands, but a 0. On Linux this appears to
work as intended.
AUTHOR
Arthur Corliss (corliss@digitalmages.com)
LICENSE AND COPYRIGHT
This software is licensed under the same terms as Perl, itself. Please see http://dev.perl.org/licenses/ for more information. (c) 2005, Arthur Corliss (corliss@digitalmages.com)