----- Original Message -----
Sent: Wednesday, June 13, 2001 10:06
AM
Subject: RE: static,synchronized and
classloaders
That is what I am seeing with my servlets. I have the same
class file in each context's web-inf/classes directory and it is keeping the
static members independent from the other context. I have a static instance of
a helper class in my servlet that wraps a properties file. I wanted to make
the helper class's members static so I could share them between servlets when
I thought of this possible issue - but I didn't realize that by making a
static variable in my servlet was testing the same issue in a different way,
hence the lightbulb as I was typing my reply.
So I would assume that the web-inf/lib classes would work the
same way, since they are loaded by the webapp's classloader.
Charlie
-----Original
Message-----
From: Jeff Trent [mailto:[EMAIL PROTECTED]]
Sent: Wednesday, June 13, 2001 9:41 AM
To: [EMAIL PROTECTED]
Subject: Re:
static,synchronized and classloaders
Are you saying that I don't need different JVMs to handle each
of my webapps if I move the JAR files that I have in my classpath down into
the lib directory of the webapp? I have a problem in that this JAR I'm
using in several of my webapp contexts uses static class members to carry
configuration information that gets corrupted by the very next webapp that
initializes the same shared library with different configuration
information.
thanks,
jeff
----- Original Message -----
From:
Cox, Charlie
To: '[EMAIL PROTECTED]'
Sent: Wednesday, June 13, 2001 8:40 AM
Subject: RE: static,synchronized and classloaders
I'm not sure what you mean by abc.MyClass and xyz.MyClass as
the class in question is in the same package in both contexts.
This archive link from Craig McClanahan(thank you Craig) gives
a good explaination of classloaders:
http://www.mail-archive.com/[email protected]/msg13260.html
Based upon this, the
individual web app classloader does not know about the other webapp
classloaders or the classes that they have loaded. That's why I think MyObject
is treated as two classes since it is loaded by two different loaders at the
same level in the class-loader heirarchy. I am currently using the same
servlet class under two class loaders. It is not throwing any errors. The
difference in my contexts is in my properties file that is context-specific
and loaded by the servlet.
Actually now that I think about it, I do have a static field
that is remaining context-specific in my servlet, therefore it must be two
different Class objects representing my class; therefore two different
instances of my static members(confusing isn't it?).
I guess I answered my own question. ;) And since I already
typed this email, I'll send it anyway and hopefully someone else will find it
useful.
you can synchonize on the class by using the 'this' object(I
am doing it). I'm just not sure if 'this' is available for static classes.I
would think that it is.
Charlie
-----Original Message-----
From: Luba Powell [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, June 12, 2001 3:50 PM
To: [EMAIL PROTECTED]
Subject: Re:
static,synchronized and classloaders(was:Java Question)
Also, look if identical files are generated based on 2
different context:
abc.MyClass is not the same as
xyx.MyClass. If 2 class loaders
load from
identical class files - JVM verifier should throw the exception
before a second object is created. If this doesn't
happen - this is a
serious bug.
Also it is not possible to synchronize
on the class - only on the method
and a variable that
is an object
----- Original Message -----
From: Cox, Charlie
To:
'[EMAIL PROTECTED]'
Sent: Tuesday, June
12, 2001 3:35 PM
Subject: RE: static,synchronized and
classloaders(was:Java Question)
Now is this true for when I have multiple contexts mapped to
the same docbase? I have seen on this list that Tomcat loads the
classes(in web-inf/classes) independently for each context and passing
MyObject class instance between contexts is not the same 'MyObject' class in
the second context even though it is the same code. Since it is not the same
class I would assume that I would have two instances of a static method/field.
And if it is synchronized on a static member(or the class itself) it would
only be synchonized for this context.
I'm really not sure what I would have if the class is static.
Thoughts?
Charlie
-----Original Message-----
From: Pae Choi [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, June 12, 2001 2:42 PM
To: [EMAIL PROTECTED]
Subject: Re:
Java Question
When you access the 'synchronized' static method, it locks its
class.
so this will ensure the thread-safe access.
Otherwise, the result is
unknown.
Pae
> I have looked all over and can't find the answer to this
simple question.
> If you use a static method, do
you have to synchronize it in case other
> people
may access it at the same time. For example, I have a static Utility
> class to do date calculations. The method
Utility.getMonth(String date)
> takes in a full
date string, parses it, and returns just the month value.
> If 5 different people all using the website attempt to use
> Utility.getMonth(String date) at the same time
for different dates, will it
> return the right
results? If not, do I have to synchronize it or something
> in case multiple users attempt to access it?
>
> I know this is not
really related to tomcat, but since I am using tomcat,
> and everyone else using tomcat is also a java developer, I figured
this is
> the best place I can ask.
>
> Thanks for any
help!!!
>
> Brandon
>
