Normally in servlet the system makes a single instance of the servlet and then creates a new thread for each user request with multiple concurrent threads running, if a new request comes while a previous request is still executing then multiple threads may access the data simultaneously which may result dirty read in some cases. It can be prevented by implementing SingleThreadModel interface.
Syntax:
Public class myServlet extends HttpServlet implements SingleThreadModel{}
This interface has no methods, it is only for, to tell the container that there is never more than one request thread accessing a single instance of the servlet. It does so by queuing all the requests and passing one at a time to the servlet. By this performance goes down because many times the server remains idle, for example when a request is executing and waiting for an I/O then the server has nothing to do.It is designed to protect the instance variables. It can not help class variables.
Now the SingleThreadModel is deprecated from servlet API.
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