on 1/27/00 12:52 AM, David Warnock <[EMAIL PROTECTED]> wrote:
> I do take your point about dynamically running services and I also have
> read Jon's message that services are not supposed to be singletons. If
> singleton services are not supported then I agree with the -1, otherwise
> I guess we can use the actual service as a proxy onto a singleton that
> does the real work.
No, you don't understand the point of having Services. The services
themselves should not be singletons, the TurbineServices object IS a
singleton...it brokers out other objects that need to act like services.
The reason for creating Services API is that what is happening is that we
are creating many many many singleton's by copying and pasting a similar
chunk of code over and over again to create singletons...
public static TurbineServices getInstance() {
if (instance == null) {
synchronized (TurbineServices.class) {
if (instance == null) {
instance = new TurbineServices();
services = new Hashtable(5);
}
}
}
return instance;
}
There are two way to effectively create a Singleton. The first way is with
the above piece of code, that in my opinion is a true singleton. The second
way is to simply hold on to a reference to an object within a singleton. So,
lets have a simple Singleton who's job it is to load services (this is the
TurbineServices object) and hold those services within a hashtable
(effectively holding on to a reference of an instance of an object).
I could see re-doing all the module/*Loaders to be Services as well since
they are essentially just TurbineServices objects as well.
Brett's suggestions are simply a clarification of what is already there. His
proposals simply fix the issues with casting that we are starting to run
into.
> I do feel myself that singletons are very handy in services for the same
> reasons that servlets run better as singletons with multiple threads.
Right, but a servlet isn't really a singleton. It is simply the second way
(that I described above) for effectively creating the same thing as a
singleton. Essentially, a Service is just the equivalent of a simple servlet
engine.
-jon
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