I would PERSONALLY recommend that you DON'T go to terracotta just to
get a unique integer sequence :)
ms
On Mar 1, 2007, at 9:35 AM, Jean-François Veillette wrote:
I have never tried but, look at this demo, this look promising !
http://www.terracottatech.com/TC_container.html
- jfv
Le 07-03-01 à 00:55, Mike Schrag a écrit :
In Java, static variables are unique per-class-per-class-loader.
That is, if you have the same class loaded in two separate class
loaders, they will have independent static variables. Likewise,
obviously, if you run two JVM's, the static variables will not be
shared. WO instances each run in their own JVM's, completely
unshared (well, as far as you're concerned at the level you're
writing code). You can NOT count on static variables sharing
across instances. You can only count on static variables being
available in a SINGLE instance, and even then only in a SINGLE
class loader (though it just so happens that your entire app is
loaded in a single class loader, so that part isn't going to get
you). If you're counting on two instances of WO sharing a static
variable, you better start preparing yourself now, because you're
about to have your heart broken. If you need unique IDs across
instances, there are several techniques, but the least pain is to
just use sequence generators from your database and let the
database handle the concurrency and synchronization.
On Feb 28, 2007, at 9:32 PM, Florijan Stamenkovic wrote:
Hi Jerry,
Wow, this concept never really occurred to me. I indeed thought
that static variables ARE shared across applications running in
the same VM. I will have to test this, but supposing it is as you
say it is, I am screwed, because:
I have some code that synchronizes on a statically declared
variable in my SessionWorker class. SessionWorker is a class to
which RMI calls on Session are forwarded to. I use this
synchronization to generate unique numbers that are not keys in
the tables I am generating them in. I can not make keys out of
them due to their specific nature (it is guaranteed that the same
table will contain records with the same values in these fields,
although in another context they are unique). Thus the
synchronization. I am aware that even if my original idea is OK,
and this works across WOApp instances, it would only work on
single machine deployment. This concept starts to melt down.
Any comments or suggestions? Do I have to switch to stored
procedures to accomplish the above???
Singleton... I was so dumb to overlook that.
Many thanks for the info,
Florijan
Hi, Florijan,
The WOApplication class is a singleton for any WebObjects
application. From the first paragraph of the JavaDoc on
WOApplication:
The primary role of the WOApplication class is to
coordinate the
handling of HTTP requests. Each application must have exactly
one WOApplication object. The application object receives...
Honestly, I've never considered the possibility that a static
variable declared for a class in one application is shared with
any other application using that same class within the same Java
Virtual Machine. I don't think this is true, and if it is, there
are a few things about static variables that I will have to
rethink before this bites me. Whether true or not, the variable
wouldn't be shared between JVM's.
That's why Robert Walker was suggesting scheduling outside the
application.
So... has anyone any information on static variables in a class
shared between separate applications on the JVM if two
applications use that same class?
Regards,
Jerry
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