The document discusses the SingleThreadModel interface in servlets. It is a marker interface with no methods that ensures a servlet can handle only one request at a time. Implementing this interface guarantees that no two threads will concurrently execute the service method of that servlet, as the servlet container will maintain a pool of servlet instances and each request will use a separate instance. This allows servlets to manage stateful information for each user through instance variables without needing synchronization.

1. Single Thread Interface in Servlet
Prof. Neeraj Bhargava
Kapil Chauhan
Department of Computer Science
School of Engineering & Systems Sciences
MDS University, Ajmer

2. Introduction
 The servlet programmer should implement
SingleThreadModel interface to ensure that servlet can
handle only one request at a time.
 It is a marker interface, means have no methods.

3. How Single Thread works

4. Cont..
 A server that loads a SingleThreadModel servlet must
guarantee, according to the Servlet API
documentation, "that no two threads will execute
concurrently the service method of that servlet.“
 To accomplish this, each thread uses a free servlet
instance from the pool.

5. Single Thread working
 A servlet that connects to a database sometimes needs
to perform several database commands atomically as
part of a single transaction.
 Normally, this would require the servlet to
synchronize around the database commands (letting it
manage just one request at a time) or to manage a pool
of database connections where it can "check out" and
"check in" connections (letting it support multiple
concurrent requests).

6. Cont…
 By instead implementing SingleThreadModel and
having one "connection" instance variable per servlet,
a servlet can easily handle concurrent requests by
letting its server manage the servlet instance pool

7. Key Point
 When SingleThreadModel is implemented, the Servlet
container gives guarantee that only one request is
honoured or handled at a time by one servlet object.
 Or to say, no two threads execute concurrently in the
same service() method.
 The interface assures thread-safe servlets.

8. Cont..
 SingleThreadModel means you are making a particular
Servlet not multithreaded.
 Multiple concurrent requests will be executed with one
Servlet instance but in different threads of which only
one is permitted.
 Use SingleThreadModel when the servlet preserves the
state of the client (specific to client) in instance
variables.

9. Assignment
 Explain Single thread Interface in java with suitable
example.