[Zope3-dev] Zope3 LifeCycle Events

[Ulrich Eck]

About Implementing LifeCycle Events for Z3


While prototyping a Task Schedule for Zope3 i thought about 
LifeCycle Events for Z3. Right now there is no way for any 
component to find out when zope starts or stops.

For a Task Schedule there needs to be some Thread that 
takes care about executing Tasks when their time is come.

Our first approach was to start a TimeEventProducer that 
publishes an ITimeEvent every n sec/min/hour. Guido mentioned
that this would be ineffective for sites that schedule events
only sometimes - i have a new solution for this. To publish the
TimeEvent we need a Path to a local EventService 
(we were talking about requiring an EventService in the RootFolder 
and therefore create it automatically).
We can then send a TimeEvent to the persistently subscribed
Schedules whose process there effective Tasks then.
The TimeEventProducer runs in a seperate Thread or from 
outside Zope3.

This is really a messy implementation i think.

Things would be much easier if there where LifeCycle Events 
for Zope3 e.g.:

  * ZopeStartupEvent: Is published after all setup is done when 
    starting a Zope-Instance

  * ZopeRefreshEvent: Is publish when the modules should be reloaded
    This could help to implement some equivalent to Refresh in Z2

  * ZopeShutdownEvent: Is published before any shutdownprocess begins
    (probably hooks into shutdown and signals)

When a Zope3-Instance process is started the EventService in the 
RootFolder is connected and a ZopeStartupEvent is published.
All persistently subscribed Components are "woken-up" and allowed
to e.g. register themself within a global service or do some
work that is needed at startup (e.g. start a Thread for the Scheduler)

When shutting down Zope via Web or CTRL-C the ZopeShutdownEvent is
published and all "active" components can cleanup before the
process finishes.

This would generalize the approach i needed to work out
for every component that is interested in the LifeCycle of
a Zope-Process.

What do others thing about that ??

Should i go on and try to prototype this one ??

thanks for your comments,

Ulrich Eck