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The moose likes Threads and Synchronization and the fly likes SIngleThreadModel Big Moose Saloon
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Dean Jones

Joined: Jun 18, 2002
Posts: 24
what is the SIngleThreadModel in the servlets
does it mean that our servlet will be from any knd of synchronizartion problems

Dean Jones
Roy Ben Ami
Ranch Hand

Joined: Jan 13, 2002
Posts: 732
yes you are correct.. but you must realize that it creates an instance of the servlet for every request! so its is very resource consuming servlet... usually i wouldnt recoomend using it.
Jim Yingst

Joined: Jan 30, 2000
Posts: 18671
Also, it doesn't necessarily free you from any synchronization problems. Since as Roy noted you can still have multiple threads active simultaneously (but using different Servlet instances), you must be careful about accessing static members of your Servlet class. Or about accessing any other shared resources outside the Servlet class itself. Really, SingleThreadModel is of very limited use.

"I'm not back." - Bill Harding, Twister
Anthony Villanueva
Ranch Hand

Joined: Mar 22, 2002
Posts: 1055
There is only one servlet instance per registered servlet. Normally, when concurrent requests are handled by the web server, threads are spawned which executes the service() method of the servlet. Instance variables are not thread safe, but local variables within the service() method are. The request object is also "localized" per thread.
According to the Servlet specs, when a servlet implements the SingleThreadModel interface (which is an empty "tag" interface) and concurrent requests are handled by the web server, the container is supposed to create a new servlet instance per request. It is possible that the container will pool these servlet instances. it is also possible that the container will serialize, i.e. queue, the requests per instance. It is possible that the container implementation is a combination of these.
Since there are now multiple servlet instances handling each request, the instance variables are now thread safe.
In either case, however, if any servlet static variables are defined, these will NOT be thread safe unless you explicitly make it so with custom code.
I agree. Here's the link:
subject: SIngleThreadModel
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