NAME¶
Proc::Reliable -- Run external processes reliably with many options.
SYNOPSIS¶
use Proc::Reliable;
Create a new process object
$myproc = Proc::Reliable->new();
Run a subprocess and collect its output
$output = $myproc->run("/bin/ls -l");
Check for problems
if($myproc->status()) {
print("problem!\n");
}
Run another subprocess, keeping stdout and stderr separated. Also, send the
subprocess some data on stdin.
$msg = "Hello World\n");
$p->want_single_list(0);
$stdout = $p->run("/usr/bin/fastmail - foo@bar.com", $msg);
if($p->status()) {
print("problem: ", $p->stderr(), "\n");
}
Another way to get output
($stdout, $stderr, $status, $msg) = $p->run("/bin/ls -l");
OPTIONS¶
Run Modes
$p->run("shell-command-line"); # Launch a shell process
$p->run("cmdline", "data"); # Launch a shell process with stdin data
$p->run(["cmd", "arg1", ...]); # Bypass shell processing of arguments
$p->run(sub { ... }); # Launch a perl subroutine
$p->run(\&subroutine); # Launch a perl subroutine
Option settings below represent defaults
$p->num_tries(1); # execute the program only once
$p->time_per_try(60); # time per try 60 sec
$p->maxtime(60); # set overall timeout
$p->time_btw_tries(5); # time between tries 5 sec
$p->want_single_list(); # return STDOUT and STDERR together
$p->accept_no_error(); # Re-try if any STDERR output
$p->pattern_stdout($pat); # require STDOUT to match regex $pat
$p->pattern_stderr($pat); # require STDERR to match regex $pat
$p->allow_shell(1); # allowed to use shell for operation
$p->child_exit_time(1.0); # timeout for child to exit after it closes stdout
$p->sigterm_exit_time(0.5); # timeout for child to exit after sigterm
$p->sigkill_exit_time(0.5); # timeout for child to exit after sigkill
$p->input_chunking(0); # feed stdin data line-by-line to subprocess
$p->stdin_error_ok(0); # ok if child exits without reading all stdin
$p->stdout_cb(undef); # callback function for line-by-line stdout
$p->stderr_cb(undef); # callback function for line-by-line stderr
Getting output
$out = $p->stdout(); # stdout produced by last run()
$err = $p->stderr(); # stderr produced by last run()
$stat = $p->status(); # exit code produced by last run()
$msg = $p->msg(); # module messages produced by last run()
Debug
Proc::Reliable::debug($level); # Turn debug on
OVERVIEW¶
Proc::Reliable is a class for simple, reliable and configurable subprocess
execution in perl. In particular, it is especially useful for managing the
execution of 'problem' programs which are likely to fail, hang, or otherwise
behave in an unruly manner.
Proc::Reliable includes all the functionality of the backticks operator and
system() functions, plus many common uses of
fork() and
exec(),
open2() and
open3(). Proc::Reliable incorporates
a number of options, including sending data to the subprocess on STDIN,
collecting STDOUT and STDERR separately or together, killing hung processes,
timouts and automatic retries.
DESCRIPTION¶
A new process object is created by
$myproc = Proc::Reliable->new();
The default will run a subprocess only once with a 60-second timeout. Either
shell-like command lines or references to perl subroutines can be specified
for launching a process in background. A simple list process, for example, can
be started via the shell as
$out = $myproc->run("ls");
To separate stdout, stderr, and exit status:
($out, $err, $status, $msg) = $myproc->run("ls");
The output data is also stored within the $myproc object for later retrieval.
You can also run a perl subroutine in a subprocess, with
$myproc->run(sub { return <*>; });
The
run Method will try to run the named process. If the process times
out (after
time_per_try seconds) or has an error defined as
unacceptable and you would like to re-run it, you can use the
num_tries
option. Use the
time_btw_tries option to set the number of seconds
between runs. This can repeat until
maxtime seconds have elapsed.
When using
num_tries, the user can specify what constitutes an
unacceptable error of STDOUT or STDERR output -- i.e. demanding a retry. One
common shorthand is to have the
run method retry if there is any return
from STDERR.
$myproc->accept_no_error(); # Re-try if any STDERR
$myproc->pattern_stdout($pat); # require STDOUT to match regex $pat
$myproc->pattern_stderr($pat); # require STDERR to match regex $pat
Subprocess completion is detected when the process closes all filehandles. The
process must then exit before child_exit_time expires, or it will be killed.
If the subprocess does not exit, it is sent a TERM signal unless
sigterm_exit_time is 0. then if it does not exit before sigterm_exit_time
expires, it is sent a KILL signal unless sigkill_exit_time is 0. then if it
does not exit before sigkill_exit_time expires an error is generated. waiting
is done in 0.01 second increments.
Proc::Reliable is not MT-Safe due to signals usage.
METHODS¶
The following methods are available:
- new (Constructor)
- Create a new instance of this class by writing either
$proc = new Proc::Reliable; or $proc = Proc::Reliable->new();
The new method accepts any valid configuration options:
$proc = Proc::Reliable->new('maxtime' => 200, 'num_tries' => 3);
- run
- Run a new process and collect the standard output and standard error via
separate pipes.
$out = $proc->run("program-name");
($out, $err, $status, $msg) = $proc->run("program-name");
by default with a single return value, stdout and stderr are combined to a
single stream and returned. with 4 return values, stdout and stderr are
separated, and the program exit status is also returned. $msg contains
messages from Proc::Reliable when errors occur. Set
want_single_list(1) to force stdout and stderr to be combined, and
want_single_list(0) to force them separated. The results from
run() are stored as member data also:
$proc->want_single_list(0);
$proc->run("program");
if($proc->status) {
print($proc->stderr);
exit;
}
else {
print($proc->stdout);
}
Program exit status is returned in the same format as exec(): bits
0-7 set if program exited from a signal, bits 8-15 are the exit status on
a normal program exit.
You can also set up callbacks to run a function of your choice as each line
of stdout and stderr is produced by the child process using the stdout_cb
and stderr_cb options.
There are a number of other options. You can also feed the forked program
data on stdin via a second argument to run():
$myinput = "hello\ntest\n";
$output = $proc->run("program-name", $myinput);
The first option to run() supports three forms: 1) string containing
command string to execute. this incurs shell parsing. 2) arrayref
containing split command string to execute. this bypasses shell parsing.
3) coderef to perl function. The first two options are executed via
exec(), so the specifics of incurring shell parsing are the same.
The second option to run() supports two forms: 1) string containing
data to feed on stdin 2) stringref pointing to data to feed on stdin
You can start execution of an independent Perl function (like
"eval" except with timeout, retries, etc.). Simply provide the
function reference like
$output = $proc->run(\&perl_function);
or supply an unnamed subroutine:
$output = $proc->run( sub { sleep(1) } );
The run Method returns after the the function finishes, one way or
another.
- debug
- Switches debug messages on and off -- Proc::Reliable::debug(1)
switches them on, Proc::Reliable::debug(0) keeps Proc::Reliable
quiet.
- maxtime
- Return or set the maximum time in seconds per run method call.
Default is 300 seconds (i.e. 5 minutes).
- num_tries
- Return or set the maximum number of tries the run method will
attempt an operation if there are unallowed errors. Default is 5.
- time_per_try
- Return or set the maximum time in seconds for each attempt which
run makes of an operation. Multiple tries in case of error can go
longer than this. Default is 30 seconds.
- time_btw_tries
- Return or set the time in seconds between attempted operations in case of
unacceptable error. Default is 5 seconds.
- child_exit_time
- When the subprocess closes stdout, it is assumed to have completed normal
operation. It is expected to exit within the amount of time specified. If
it does not exit, it will be killed (with SIGTERM). This option can be
disabled by setting to '0'. Values are in seconds, with a resolution of
0.01.
- sigterm_exit_time
- If the time_per_try or max_time has been exceeded, or if
child_exit_time action has not succeeded, the subprocess will be
killed with SIGTERM. This option specifies the amount of time to allow the
process to exit after closing stdout. This option can be disabled by
setting to '0'. Values are in seconds, with a resolution of 0.01.
- sigkill_exit_time
- Similar to sigterm_exit_time, but a SIGKILL is sent instead of a
SIGTERM. When both options are enabled, the SIGTERM is sent first and
SIGKILL is then sent after the specified time only if the subprocess is
still alive. This option can be disabled by setting to '0'. Values are in
seconds, with a resolution of 0.01.
- input_chunking
- If data is being written to the subprocess on stdin, this option will
cause the module to split() the input data at linefeeds, and only
feed the subprocess a line at a time. This option typically would be used
when the subprocess is an application with a command prompt and does not
work properly when all the data is fed on stdin at once. The module will
feed the subprocess one line of data on stdin, and will then wait until
some data is produced by the subprocess on stdout or stderr. It will then
feed the next line of data on stdin.
- stdout_cb
- Set up a callback function to get stdout data from the child line-by-line.
The function you supply will be called whenever the child prints a line
onto stdout. This is the only way to get output from the child while it is
still running, the normal method will give you all the output at once
after the child exits.
- stderr_cb
- Similar to stdout_cb for stderr data.
REQUIREMENTS¶
I recommend using at least perl 5.003.
AUTHORS¶
Proc::Reliable by Dan Goldwater <dgold at zblob dot com>
Based on Proc::Short, written by John Hanju Kim <jhkim@fnal.gov>.
Contributions by Stephen Cope and Jason Robertson.
COPYRIGHT¶
Copyright 2001 by Dan Goldwater, all rights reserved. Copyright 1999 by John
Hanju Kim, all rights reserved.
This program is free software, you can redistribute it and/or modify it under
the same terms as Perl itself.