Multiple KJS & Static Varibles

Hi
We have an application running on iAS6.0 SP3 on Solaris Box with 4 KJS
processes. We have a Java Class which have static varibles in it. When we
access the class, the class is getting loaded 4 times, one on each KJS
process which is causing 4 copies of the static data. So, each time we hit a
new KJS our previous values are lost. Are we doing some thing wrong and this
is the expected behavious. If so how do we go about finding an alternate
way?
Thanks in advance,
Bhamu
Eclipse Networks Inc.

Yes, this is expected behavior. (And is true in any multi-JVM
environment, not just iAS.)
Generally, you should avoid having one variable that must remain unique
in an entire cluster. By definition, this will limit your scalability.
That said, you could consider storing the information in a
ServletContext attribute. iAS will automagically distribute the value to
all of the KJS engines (assuming that you are using DSYNC). It will
perform some caching of the attribute so that you will minimize the
affect on your application.
David
Bhamu wrote:
Hi
We have an application running on iAS6.0 SP3 on Solaris Box with 4 KJS
processes. We have a Java Class which have static varibles in it. When we
access the class, the class is getting loaded 4 times, one on each KJS
process which is causing 4 copies of the static data. So, each time we hit a
new KJS our previous values are lost. Are we doing some thing wrong and this
is the expected behavious. If so how do we go about finding an alternate
way?
Thanks in advance,
Bhamu
Eclipse Networks Inc.

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(1) Thread A read counter from Database as 0
(2) Thread A increment counter to 1
(3) Thread B read counter from Database as 0
(4) Thread A write counter as 1 to database
(5) Thread B increment counter to 1
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What I wish is
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(2) Thread A increment counter to 1
(4) Thread A write counter as 1 to database
(3) Thread B read counter from Database as 1
(5) Thread B increment counter to 2
(6) Thread B write counter as 2 to database
Thanks you.
Edited by: yccheok on Oct 27, 2009 8:39 PM

This is my understanding of the issue (you should research it further on you own to get a better understanding):
I suggest you use local variables (ie, defined within a function), and keep away from static variables. Those local variables are thread safe. If you call functions within functions, its still thread safe. If you read or write to one record in a database using sql, its thread safe (you dont need a transaction). If you read/write to multiple tables and/or records, you probably need a transaction. Servlets are thread safe. You usually dont need the 'synchronized' word anywhere unless you have a function updating/reading a static variable and therefore want to ensure only one user is accessing the static varible at a time. Also do so if you are writing to some resource (such as a file, a variable in applicaton scope, session scope, or resource that everyone uses such as email server). You dont want more than one person at a time to write to it). Note the database is one of of those resources that is handled by transactions rather than the the synchronized keyword (the synchronized keyword is applied to your application only (not other applications that someone is running), whereas the transaction ensures all applications are locked out while you update those records in the database).
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