Steven Haryanto

NAME

Process::Govern - Run child process and govern its various aspects

VERSION

version 0.12

SYNOPSIS

To use via command-line (in most cases):

 % govproc \
       --timeout 3600 \
       --log-stderr-dir        /var/log/myapp/ \
       --log-stderr-size       16M \
       --log-stderr-histories  12 \
   /path/to/myapp

To use directly as Perl module:

 use Process::Govern qw(govern_process);
 govern_process(
     name       => 'myapp',
     command    => '/path/to/myapp',
     timeout    => 3600,
     log_stderr => {
         dir       => '/var/log/myapp',
         size      => '16M',
         histories => 12,
     },
 );

DESCRIPTION

Process::Govern is a child process manager. It is meant to be a convenient bundle (a single parent/monitoring process) for functionalities commonly needed when managing a child process. It comes with a command-line interface, govproc.

Background story: I first created this module to record STDERR output of scripts that I run from cron. The scripts already log debugging information using Log::Any to an autorotated log file (using Log::Dispatch::FileRotate, via Log::Any::Adapter::Log4perl, via Log::Any::App). However, when the scripts warn/die, or when the programs that the scripts execute emit messages to STDERR, they do not get recorded. Thus, every script is then run through govproc. From there, govproc naturally gets additional features like timeout, preventing running multiple instances, and so on.

Currently the following governing functionalities are available:

  • logging of STDOUT & STDERR output to an autorotated file

  • execution time limit

  • preventing multiple instances from running simultaneously

  • load watch

  • autorestart

In the future the following features are also planned or contemplated:

  • CPU time limit

  • memory limit

    With an option to autorestart if process' memory size grow out of limit.

  • other resource usage limit

  • fork/start multiple processes

  • set (CPU) nice level

  • set I/O nice level (scheduling priority/class)

  • limit STDIN input, STDOUT/STDERR output?

  • trap/handle some signals for the child process?

  • set UID/GID?

  • provide daemon functionality?

  • provide network server functionality?

    Inspiration: djb's tcpserver.

  • set/clean environment variables

EXIT CODES

Below is the list of exit codes that Process::Govern uses:

  • 124

    Timeout. The exit code is also used by timeout.

  • 202

    Another instance is already running (when single_instance option is true).

FUNCTIONS

govern_process(%args) => INT

Run child process and govern its various aspects. It basically uses IPC::Run and a loop to check various conditions during the lifetime of the child process. Known arguments (required argument is marked with *):

  • command* => STR | ARRAYREF

    Program to run. Passed to IPC::Run's start().

  • name => STRING

    Should match regex /\A\w+\z/. Used in several places, e.g. passed as prefix in File::Write::Rotate's constructor as well as used as name of PID file.

    If not given, will be taken from command.

  • timeout => INT

    Apply execution time limit, in seconds. After this time is reached, process (and all its descendants) are first sent the TERM signal. If after 30 seconds pass some processes still survive, they are sent the KILL signal.

    The killing is implemented using IPC::Run's kill_kill().

    Upon timeout, exit code is set to 124.

  • show_stderr => BOOL (default: 1)

    Can be used to turn off STDERR output. If you turn this off and set log_stderr, STDERR output will still be logged but not displayed to screen.

  • log_stderr => HASH

    Specify logging for STDERR. Logging will be done using File::Write::Rotate. Known hash keys: dir (STR, defaults to /var/log, directory, preferably absolute, where the log file(s) will reside, should already exist and be writable, will be passed to File::Write::Rotate's constructor), size (INT, also passed to File::Write::Rotate's constructor), histories (INT, also passed to File::Write::Rotate's constructor), period (STR, also passed to File::Write::Rotate's constructor).

  • show_stdout => BOOL (default: 1)

    Just like show_stdout, but for STDOUT.

  • log_stdout => HASH

    Just like log_stderr, but for STDOUT.

  • single_instance => BOOL

    If set to true, will prevent running multiple instances simultaneously. Implemented using Proc::PID::File. You will also normally have to set pid_dir, unless your script runs as root, in which case you can use the default /var/run.

  • pid_dir => STR (default: /var/run)

    Directory to put PID file in. Relevant if single is set to true.

  • on_multiple_instance => STR

    Can be set to 'exit' to silently exit when there is already a running instance. Otherwise, will print an error message 'Program <NAME> already running'.

  • load_watch => BOOL (default: 0)

    If set to 1, enable load watching. Program will be suspended when system load is too high and resumed if system load returns to a lower limit.

  • load_high_limit => INT|CODE (default: 1.25)

    Limit above which program should be suspended, if load watching is enabled. If integer, will be compared against Sys::LoadAvg's LOADAVG_1MIN value. Alternatively, you can provide a custom routine here, code should return true if load is considered too high.

  • load_low_limit => INT|CODE (default: 0.25)

    Limit below which program should resume, if load watching is enabled. If integer, will be compared against Sys::LoadAvg's LOADAVG_1MIN value. Alternatively, you can provide a custom routine here, code should return true if load is considered low.

  • load_check_every => INT (default: 10)

    Frequency of load checking, in seconds.

  • restart => BOOL (default: 0)

    If set to true, do restart.

Planned arguments: restart_delay, check_alive.

Return value: command exit code.

govern_process(%args) -> any

Arguments ('*' denotes required arguments):

  • command* => array|str

  • load_check_every => int (default: 10)

  • load_high_limit => code|int

  • load_low_limit => code|int

  • load_watch => bool (default: 0)

  • log_stderr => hash

    Will be passed as arguments to File::Write::Rotate.

  • log_stdout => hash

    Will be passed as arguments to File::Write::Rotate.

  • name => str

  • on_multiple_instance => str

  • restart => bool (default: 1)

  • show_stderr => bool (default: 1)

  • show_stdout => bool (default: 1)

  • single_instance => bool (default: 0)

  • timeout => int

Return value:

FAQ

Why use Process::Govern?

The main feature this module offers is convenience: it creates a single parent process to monitor child process. This fact is more pronounced when you need to monitor lots of child processes. If you use, on the other hand, separate parent/monitoring process for timeout and then a separate one for CPU watching, and so on, there will potentially be a lot more processes running on the system. Compare for example:

 % govproc --timeout 10 --load-watch CMD

which only creates one monitoring process, versus:

 % timeout 10s loadwatch CMD

which will create two parent processes (three actually, loadwatch apparently forks first).

CAVEATS

Not yet tested on Win32.

TODO

  • Govern multiple processes instead of just one

    It's only natural that we expand to this, to reduce the number of monitor process.

    We want to be able to set options for all processes or on a per-process basis. For example: when load watching, all processes can be stopped and resumed using the same high/load criteria, but some processes might want to have a different criteria. The same goes with timeout.

    Some options are for a per-process, e.g. capturing stderr.

    If we support multiple commands, e.g. commands => ['cmd1', ['cmd2', 'arg']] then we'll also need to return exit codes for each command, e.g. [0, 124].

    We should exit only after all child processes terminate. But when a child exits, a hook can be defined e.g. on_child_exit.

  • Allow specifying time point (instead of duration) for timeout?

    For example, we might want to say "this command should not run past midnight".

    In general, we might also want to allow specifying a coderef for flexible timeout criteria?

  • Print messages when stopping/resuming due to load control

    Like loadwatch does:

     Fri Mar 14 16:17:52 2014: load too high, stopping.
     Fri Mar 14 16:18:52 2014: load low, continuing.
  • Option to not use File::Write::Rotate for logging STDOUT/STDERR

    If command is output-heavy, FWR will become a significant overhead.

SEE ALSO

Process::Govern attempts (or will attempt, some day) to provide the functionality (or some of the functionality) of the builtins/modules/programs listed below:

  • Starting/autorestarting

    djb's supervise, http://cr.yp.to/daemontools/supervise.html

  • Pausing under high system load

    loadwatch. This program also has the ability to run N copies of program and interactively control stopping/resuming via Unix socket.

    cPanel also includes a program called cpuwatch.

  • Preventing multiple instances of program running simultaneously

    Proc::PID::File, Sys::RunAlone

  • Execution time limit

    timeout.

    alarm() (but alarm() cannot be used to timeout external programs started by system()/backtick).

    Sys::RunUntil

  • Logging

    djb's multilog, http://cr.yp.to/daemontools/multilog.html

Although not really related, Perinci::Sub::Wrapper. This module also bundles functionalities like timeout, retries, argument validation, etc into a single function wrapper.

HOMEPAGE

Please visit the project's homepage at https://metacpan.org/release/Process-Govern.

SOURCE

Source repository is at https://github.com/sharyanto/perl-Process-Govern.

BUGS

Please report any bugs or feature requests on the bugtracker website https://rt.cpan.org/Public/Dist/Display.html?Name=Process-Govern

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.

AUTHOR

Steven Haryanto <stevenharyanto@gmail.com>

COPYRIGHT AND LICENSE

This software is copyright (c) 2014 by Steven Haryanto.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.




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