Products.cron4plone 1.1.3

Product description

Cron4Plone can do scheduled tasks in Plone, in a syntax very like *NIX systems’ cron daemon. It plugs into Zope’s ClockServer machinery.

optionally cron4plone also uses unimr.memcachedlock to make sure that only one task is running at a time, even when using a distributed environment like multiple zeo clients on multiple machines.

Installation

1. Configure the ticker in the buildout (or zope.conf):

   [instance]
   ...
   eggs =
       Products.cron4plone
   
   zope-conf-additional =
     <clock-server>
         method /<your-plone-site>/@@cron-tick
         period 60
     </clock-server>

1.1 Optionally use memcached server(s) to share locks:

[instance]
...
eggs =
    Products.cron4plone
    unimr.memcachedlock


you can specify where you are running your memcached servers in the
MEMCACHEDLOCK_SERVERS environment variable, e.g.:

zope-conf-additional =
  <environment>
      MEMCACHEDLOCK_SERVERS <ip/hostname of host1>:<port>,<ip/hostname of host2>:<port>
  </environment>

1.2 Optionally install memcached from buildout

A memcached server is a standalone server process which you can either get via your favourite package manager (for debian / ubuntu: apt-get install memcached)

but you can also build it from a buildout:

parts +=
    memcached
    memcached-ctl
    supervisor

[memcached]
recipe = zc.recipe.cmmi
url = http://memcached.googlecode.com/files/memcached-1.4.0.tar.gz
extra_options = --with-libevent=${libevent:location}

[memcached-ctl]
recipe = ore.recipe.fs:mkfile
path = ${buildout:bin-directory}/memcached
mode = 0755
content =
 #!/bin/sh
 PIDFILE=${memcached:location}/memcached.pid
    case "$1" in
      start)
       ${memcached:location}/bin/memcached -d -P $PIDFILE
        ;;
      stop)
        kill `cat $PIDFILE`
        ;;
      restart|force-reload)
        $0 stop
        sleep 1
        $0 start
        ;;
      *)
        echo "Usage: $SCRIPTNAME {start|stop|restart}" >&2
        exit 1
        ;;
    esac

You need to have the libevent development libraries (apt-get install libevent-dev) or in buildout:

[libevent] recipe = zc.recipe.cmmi url = http://www.monkey.org/~provos/libevent-1.3b.tar.gz

Make sure that the libevent.so (shared object) file is in your LD_LIBRARY_PATH before you start the memcached server if you build the libevent library from the buildout.

If you use supervisor, you can add a line like this to start the memcached server: 10 memcached ${buildout:directory}/parts/memcached/bin/memcached

2. Configure the scheduled tasks

   In the Plone site setup, go to the cron4plone configuration. This form can be used to enter cron-like jobs.

   The cron job should have 5 elements: minute, hour, day_of_month, month and command expression. For the command python and tal expression can be used.

   definition: m h dom m command

   Examples: * 11 * * portal/@@run_me 15,30 * * * python: portal.my_tool.runThis()

3. Wait and see

   In the ZMI, go to the CronTool. If a cronjob has run the history is shown.

4

Rationale

Cron4plone uses the clockserver and allows advanced taask scheduling:

• scheduled tasks at scheduled times. E.g. I want to perform a certain task at 3 AM at the first day of the month.

• single thread running the task: We don’t want 2 threads running the same task at the same time. With only using clock server this might happen if a task takes longer than the tick period.

TODO

• Day of week is missing in cron-like syntax, add it.

• Improve doc test, currently test has basic coverage.

• Perhaps make a configuration form that allows users without cron syntax knowledge to enter jobs.

License and credits

Authors: “Huub Bouma”, mailto:bouma@gw20e.com

“Kim Chee Leong”, mailto:leong@gw20e.com

License: This product is licensed under the GNU Public License version 2. See the file LICENSE included in this product.

Parts of the code were taken from “PloneMaintenance”, http://plone.org/products/plonemaintenance by “Ingeniweb”, http://www.ingeniweb.com/. “unimr.memcachedlock”

Changelog