I know this question should be addressed to Avalon group but I am only cocoon subscriber and feel much safer with you guys :)
How should I write an avalon component that is a pure singleton? The case is I
need a component that has only ONE instance and the access is strictly
synchronized. The component cannot be pooled because AFAIU the pool can grow
over it's maximum size set in cocoon.xconf.
In Cocoon 2.1 and prior you would have your component implement the ThreadSafe interface. In Cocoon 2.2 you would add the @x-avalon.lifstyle type="singleton" meta tag to the JavaDoc for the class.
Normally I would implement a singleton with synchronized methods but I would like to make it cocoon exercise and make this a component with full lifecycle.
You can still use a "strict" singleton if you don't need access to other components, but in servlet environments heavy use of synchronization can limit the scalability of a system. Of course the opposite is also true: insufficient synchronization leads to an unstable system. It is hard to find the right balance, or to limit the points where you *need* synchronization.
--
"They that give up essential liberty to obtain a little temporary safety
deserve neither liberty nor safety."
- Benjamin Franklin