What's the difference between isThreadSafe set to true / false ?

Question

I wrote a jsp that contains the following snippet:
<%@page isThreadSafe="false" language="java" %>
<%! int count = 0; %>
<% count++; %>
<% Thread.sleep(5000); %>
You are visitor number <%= count %>
I test this by running 2 browsers at the same time, but I found there's no
difference between that isThreadSafe set to true/false in the result, and I
found there's no difference in the generated servlets' code. Will the servlet
implements the SingleThreadModel interface if the isThreadSafe is false in the
jsp? I'm using jakarta-tomcat-4.1.18-LE-jdk14.

Answer 1

Your idea about implementing SingleThreadModel is ok, though Tomcat 4.1.18 for my version also does not make any difference in generated servlet with isThreadSafe value.
However, one thing is important to remember that isThreadSafe is not a panacea to make JSPs thread safe. It actually depends on the type of variables/values u r changing.
Any local varible under _jspService is thread-safe, as all requests are unique.
For the same reason, request attributes are always thread-safe.
Class/member varibales in JSP/Servlet are not thread-safe also. From your code count is not thread safe.
Session attributes are not thread-safe, as you can access and change them using multiple browser windows from different JSPs. If u do not do that they are safe.
Application/context attributes are not thread-safe also. They can be accessed by multiple users at the same time.
However, I do not why generated servlet is not different for this version of Tomcat. May be they can tell.
Thanks.
Hafizur Rahman
SCJP