Paranoid::Process(3)

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)