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abnormal behaviour

 
Leandro Oliveira
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I wrote this jsp:
and tested it under tomcat 5.0
<%@page buffer='512kb' isThreadSafe='false'%>
<%!static int qtdInstances=0;%>
<%!static int qtdMortos=0;%>
<%{qtdInstances++;}%>
<br>
quantidade de Instancias:<%=qtdInstances%>
<br>
quantidade de mortos:<%=qtdMortos%>
<%!
public void finalize(){
qtdMortos++;
}
%>
Notice that the number of instances is only increasing, and the number of garbage-collected objects is never decresing, is it normal?? shouldn't tomcat have the instances in a pool?
 
Michael Morris
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It probably does have the instances in a pool, but that doesn't mean that it destroys the instances after each use. The whole point of pooling is to increase performance on servlets that implement SingleThreadModel so that you can use whatever instance is available when multiple requests arrive. Of course you also know that you may be waiting forever for any instance to be GCed and finalized anyway.
 
Nicholas Cheung
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Hi leandro,
One more thing to remember, the specification does not assure that the finalize() method will always be invoked.
Unlike standalone java applications, we cannot relay on the finalize() method to release the resources in Web and Enterprise applications.
Nick.
 
Leandro Oliveira
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guys, I've requested this page many times, and what I could notice was that for each request, tomcat 5.0 created a new instance of this page. Last night I did 4600 requests to this resource and 4600 objects were created, my memory usage increased linearly... I'm afraid of using singleThreadModel in a highly visited aplication, since we may have OutOfMemoryError...
 
Michael Morris
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I'm afraid of using singleThreadModel in a highly visited aplication
And I think that is the whole point. For industrial strength web apps, you should probably never use SingleThreadModel, but design your app so that they are inherently thread safe, no instance or static variables, no mutable context attributes (or synchronize them), etc. From what you say, it would appear that Tomcat 5 doesn't pool at all, but just creates a new instance on each request, that seems wasteful, but would be easier to implement than pooling.
 
Jignesh Malavia
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Originally posted by leandro oliveira:
guys, I've requested this page many times, and what I could notice was that for each request, tomcat 5.0 created a new instance of this page. Last night I did 4600 requests to this resource and 4600 objects were created, my memory usage increased linearly... I'm afraid of using singleThreadModel in a highly visited aplication, since we may have OutOfMemoryError...

Originally posted by leandro oliveira:
guys, I've requested this page many times, and what I could notice was that for each request, tomcat 5.0 created a new instance of this page. Last night I did 4600 requests to this resource and 4600 objects were created, my memory usage increased linearly... I'm afraid of using singleThreadModel in a highly visited aplication, since we may have OutOfMemoryError...

Hi,
I think you wanted to use this construct
<%!{qtdInstances++;}%>
Note the ! in <%! to make it an instance initializer. Without !, it is just a scriplet (part of the _jspService method) that will be executed for each request, hence the high value printed by <%=qtdInstances%>
Also, as Michael suggested, you probably don't want to use isThreadSafe or SingleThreadModel at all. That interface is depricated in the new version of the specs.
 
Leandro Oliveira
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you're right!!
Tomcat is pooling the objtects!!
It was a matter of coding!
Sorry for this mistake guys...
 
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