Re: multiple servlet instances?

[Nick Wesselman]

the book was actually referring to the case where isThreadSafe="false" ... it uses misleading wording, however.

"... you also need to be aware that, even if a JSP page sets the isThreadSafe attribute to false, JSP implementations are still permitted to create multiple instances of the corresponding servlet..." (my emph)

"Web Development with Java Server Pages" by Duane Fields and Mark Kolb ... p. 62 ... I just got a fax of the page in reference to a question from a client. Thanks for your help!

Nick

On Monday, October 21, 2002, at 05:22 PM, Craig R. McClanahan wrote:

On Mon, 21 Oct 2002, Nick Wesselman wrote:

Date: Mon, 21 Oct 2002 16:49:18 -0500
From: Nick Wesselman <[EMAIL PROTECTED]>
Reply-To: Tomcat Users List <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Subject: multiple servlet instances?

I was reading in a book today that "JSP implementations are still
permitted to create multiple instances of the ... servlet in order to
provide improved performance." Does Tomcat/Jasper do this? Might there
be multiple instances of a servlet (JSP-generated or otherwise) in my
JVM?

You might want to be cautious believing anything that book says about any
topic, unless it correctly explains what is really going on. What book
said this?

For anything from Servlet 2.2 on (that's quite a long while back), it is
not legal for the container to create more than one instance of a
particular servlet definition *unless* that servlet implements the
SingleThreadModel interface (or the JSP page has the
isThreadSafe="false" attribute on its <%@ page %> directive).

The other thing to note is that doing this would not improve performance
-- at best, it will have zero impact, but it's actually pretty likely to
be negative (because the container is going to have to manage the multiple
instances, because the maximum number of simultaneous requests to that
servlet is now limited to the pool size you've configured, and because
they take up more memory space).

The only reason that SingleThreadModel exists is to allow you to create a
servlet or JSP page that stores per-request state information in instance
variables of the underlying class. This is not a good programming
practice -- you should instead use local variables only, so that a single
instance of your servlet or JSP page can handle any number of simultaneous
requests.

Thanks,
Nick

Craig McClanahan


--
To unsubscribe, e-mail: <mailto:tomcat-user-unsubscribe@;jakarta.apache.org>
For additional commands, e-mail: <mailto:tomcat-user-help@;jakarta.apache.org>