> Are there any examples online to see the synchronization done in servlet?
A better strategy would be to take a class or read a book on proper
concurrency control. I can recommend "Concurrent Programming in Java" 2nd ed
by Doug Lea. This book is fairly difficult, but if you can get past the
chapter 1 (out of 4), then you will have a very good understanding of the
issues of multithreading and the parallels with a Web container should be
fairly obvious.
> Singlethreadmodel will give take care of container which has servlet in it.
> that means it will have only 1 thread activating the service() method? if so
> how does the next incoming thread get the service() handle? Please let me
> know exactly what happens with this model? is it internally implemented, or
> we have to write it?
Take my advice and *forget* STM. It is deprecated in the latest servlet
spec and was of debatable value to begin with.
Instead, learn about proper sync. control (as I mentioned above). Here are
a heuristics that I use:
* synchronize only critical code sections of your servlet
Do *not* synchronize the whole service (or doGet, doPost) method.
"Critical code" sections are those that affect (modify) shared data
(instance vars, class vars, Session attrs, and Context attrs).
For example:
public class MyServlet extends HttpServlet {
private int counter;
public void doGet(...) {
... // do some work
// update counter
synchronize (this) {
counter++;
}
... // do more work
}
}
Notice that is very little "critical code". Multiple threads executing
this doGet method will only have to "wait" (if neccessary) to update
the counter variable *not* for the whole method.
* use read-only instance and class variables
The biggest mistake novice servlet developers make is to have lots of
instance variables that store "state". Sometimes, this is unavoidable.
But consider doing the following: (a) collect these variables into a
single (or a few) objects that the servlet references and make *this*
class thread-safe, (b) only use instance/class vars for read-only
information (such as the servlet init. parameters).
* use immutable objects where appropriate
Immutable objects (such as String and primitive wrappers) are inherantly
thread-safe becuase you cannot change the data (by definition).
* use resources (objects) that are properly designed for multithreading
The perfect example of this is a DB connection pool (or a JDBC DataSource).
CPs must be *built* to be thread-safe because they are will be used
extensively by multiple threads.
This is just a starting point.
HTH,
Bryan
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