NAME

Proc::Background - Generic interface to Unix and Win32 background process management

SYNOPSIS

use Proc::Background;
timeout_system($seconds, $path_to_program, $arg1);
timeout_system($seconds, "$path_to_program $arg1");
my $proc1 = Proc::Background->new($path_to_program, $arg1, $arg2);
my $proc2 = Proc::Background->new("$path_to_program $arg1 1>&2");
$proc1->alive;
$proc1->die;
$proc1->wait;
my $time1 = $proc1->start_time;
my $time2 = $proc1->end_time;

DESCRIPTION

This is a generic interface to place programs in background processing on both Unix and Win32 platforms. This class lets you start, kill, wait on, retrieve exit values, and see if background processes are still exist.

METHODS

new path, [arg, [arg, ...]]

new 'path [arg [arg ...]]'

This creates a new background process. As exec or system may be passed an array with a single single string element containing a command to be passed to the shell or an array with more than one element to be run without calling the shell, new has the same behavior.

In certain cases new will attempt to find path on the system and fail if it cannot be found.

For Win32 operating systems:

The Win32::Process module is always used to spawn background
processes on the Win32 platform.  This module always takes a
single string argument containing the executable's name and
any option arguments.  In addition, it requires that the
absolute path to the executable is also passed to it.  If
only a single argument is passed to new, then it is split on
whitespace into an array and the first element of the split
array is used at the executable's name.  If multiple
arguments are passed to new, then the first element is used
as the executable's name.

If the executable's name is an absolute path, then new
checks to see if the executable exists in the given location
or fails otherwise.  If the executable's name is not
absolute, then the executable is searched for using the PATH
environmental variable.  The input executable name is always
replaced with the absolute path determined by this process.

In addition, when searching for the executable, the
executable is searched for using the unchanged executable
name and if that is not found, then it is checked by
appending `.exe' to the name in case the name was passed
without the `.exe' suffix.

Finally, the argument array is placed back into a single
string and passed to Win32::Process::Create.

For non-Win32 operating systems, such as Unix:

If more than one argument is passed to new, then new
assumes that the command will not be passed through the
shell and the first argument is the executable's relative
or absolute path.  If the first argument is an absolute
path, then it is checked to see if it exists and can be
run, otherwise new fails.  If the path is not absolute,
then the PATH environmental variable is checked to see if
the executable can be found.  If the executable cannot be
found, then new fails.  These steps are taking to prevent
exec() from failing after an fork() without the caller of
new knowing that something failed.

If anything fails, then new returns an empty list in a list context, an undefined value in a scalar context, or nothing in a void context.

pid

Returns the process ID of the created process. This value is saved even if the process has already finished.

alive

Return 1 if the process is still active, 0 otherwise.

die

Reliably try to kill the process. Returns 1 if the process no longer exists once die has completed, 0 otherwise. This will also return 1 if the process has already died. On Unix, the following signals are sent to the process in one second intervals until the process dies: HUP, QUIT, INT, KILL.

wait

Wait for the process to exit. Return the exit status of the program as returned by wait() on the system. To get the actual exit value, divide by 256, regardless of the operating system being used. If the process never existed, then return an empty list in a list context, an undefined value in a scalar context, or nothing in a void context. This function may be called multiple times even after the process has exited and it will return the same exit status.

start_time

Return the value that the Perl function time() returned when the process was started.

end_time

Return the value that the Perl function time() returned when the exit status was obtained from the process.

FUNCTIONS

timeout_system timeout, path, [arg, [arg...]]

timeout_system 'timeout path [arg [arg...]]'

Run a command for timeout seconds and if the process did not exit, then kill it. The location of the program must be used passed in path. While the timeout is implemented using sleep(), this function makes sure that the full timeout is reached before killing the process. The return is the exit status returned from the wait() call. To get the actual exit value, divide by 256. If something failed in the creation of the process, it returns an empty list in a list context, an undefined value in a scalar context, or nothing in a void context.

IMPLEMENTATION

Proc::Background comes with two packages, Proc::Background::Unix and Proc::Background::Win32. Currently, on the Unix platform Proc::Background it uses the Proc::Background::Unix class and on the Win32 platform Proc::Win32, which makes use of Win32::Process, is used.

The Proc::Background is package that just assigns to @ISA either Proc::Unix or Proc::Win32, which does the OS dependent work. The OS independent work is done in Proc::Background.

Use two variables to keep track of the process. $self->{_os_obj} contains the operating system object to reference the process. On a Unix systems this is the process id (pid). On Win32, it is an object returned from the Win32::Process class. When $self->{_os_obj} exists, then the program is running. When the program dies, this is recorded by deleting $self->{_os_obj} and saving the exit value $self->{_exit_value}.

Anytime alive() is called, a waitpid() is called on the process and the return status, if any, is gathered and saved for a call to wait(). This module does not install a signal handler for SIGCHLD. If for some reason, the user has installed a signal handler for SIGCHLD, then, then when this module calls waitpid(), the failure will be noticed and taken as the exited child, but it won't be able to gather the exit status. In this case, the exit status will be set to 0.

SEE ALSO

See also the Proc::Background::Unix and Proc::Background::Win32 manual pages.

AUTHOR

Blair Zajac <blair@gps.caltech.edu>

COPYRIGHT

Copyright (C) 1998-2001 Blair Zajac. All rights reserved. This package is free software; you can redistribute it and/or modify it under the same terms as Perl itself.