Threads for a servlet

[A Kumar]

Hi,

Since there exists a single instance for a servlet ...and threads are created according to the request for that servlet...

How many threads (Maximum) are allowed for servlet instance....

what if the no of requests exceed this limit...and a new request comes...

what happens to that latest request....

Regards

[David O'Meara]

This is normally a configuration setting for the container. In general are stored ina thread pool and are taken from the pool to serve client requests. In theory it would be possible for all of the threads from the worker thread pool to be accessing the same servlet with no ill effects. Consider the Front Controller pattern, for example.

When the worker threads are all being user, user requests often get held in a queue where they are waiting to be processed but have not yet been processed. This is equivalent to just making the thread sleep till it's turn comes around.

If the queue is also filled then requests just get rejected.

[A Kumar]

Hi David,

Thanks for the prompt reply!!!

Tell me whats would be the size of the request queue..Is it dependent upon the server and can the user confgiure...this....

Coming to the Front controller pattern like in struts,
will the action servlet will have one thread or multiple threads for user requests...

I know there exists only one instance...but how about the threads depending upon the user requests


And finally,
all along i thought that for a single servlet instance, we create thread for a request...but this thread would be Gc'ed once it completes the process of servicing the request.There is no way we are going to reuse the thread...
Then how come we have thread pool...Can you tell me where i am going off track about this...

Tx in advance
Regards
Probably need to revisit the servlets concepts...

[William Brogden]

The thing that is confusing you is:

we create thread for a request

In the servlet environment, the servlet engine is responsible for managing the threads that are assigned to requests. In the Tomcat configuration file we find these typical settings for a given connector:

     maxThreads="150" minSpareThreads="25" maxSpareThreads="75"   

The server starts 25 Threads initially for the request Thread pool, can create as many as 150, if the usage falls to the point where 75 threads are not in use, it will destroy some to recover resources.
Bill

[A Kumar]

Thanks William,
So the container creates CERTAIN no of threads for each servlet instance when it is deployed ...

This is pooled together in thread pool...

Is the above inference correct!!!

Tx

[Pradeep bhatt]

Originally posted by A Kumar:
Thanks William,
So the container creates CERTAIN no of threads for each servlet instance when it is deployed ...

This is pooled together in thread pool...

Is the above inference correct!!!

Tx

It is not certain number of threads for each servlets.It is the number of threads for requests for all servlets/JSPs.

[A Kumar]

Hi Pradeip,

According to Williams post..

In the servlet environment, the servlet engine is responsible for managing the threads that are assigned to requests. In the Tomcat configuration file we find these typical settings for a given connector:

code:

maxThreads="150" minSpareThreads="25" maxSpareThreads="75"

The server starts 25 Threads initially for the request Thread pool, can create as many as 150, if the usage falls to the point where 75 threads are not in use, it will destroy some to recover resources.

And according to your post

It is not certain number of threads for each servlets.It is the number of threads for requests for all servlets/JSPs.

Do you mean that 25 is the min threads for requests for all the servlets/JSPs in a single web application...

So how will the 25 threads limit be decided...?

[Pradeep bhatt]

The thread count is for the whole Tomcat.

[A Kumar]

Thanks Pradip!!!

But still i have one doubt...

threads are created when the user sends a request for a particular servlet...(first time - instance is created..later same servlet instance services)

Then how that is pooled..i mean a min limit..
[ May 30, 2006: Message edited by: A Kumar ]

[Pradeep bhatt]

You can read this article for an sample implementation of thread pools
http://www-128.ibm.com/developerworks/java/library/j-jtp0730.html

Java 5 has a ThreadPoolExecutor can pool threads. I am not sure about the timeout value for the Tomcat threads.

[William Brogden]

threads are created when the user sends a request for a particular servlet

Where did you get that idea?

In Tomcat the initial Thread pool with the minimum number of Threads is created immediately on startup. The idea being that when the first request appears, an existing Thread will be assigned.

You can verify this with Tomcat's Management application. I have been watching the Thread pool in my public server regularly. Immediately on restart it had 25 Threads - after a couple of days it was running with 50 threads in the pool.

Bill