Products.cron4plone 1.1.1

Cron4Plone can do scheduled tasks in Plone

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:[e-mail]
"Kim Chee Leong", mailto:[e-mail]

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
=========

1.1.2
-----
* Fixed bug, missing 'ConflictError' import

1.1.1
-----
* share locks with memcached

1.0 - Unreleased
----------------

* Initial release