CODEWITHSUNDEEP
javaservlets
satm12
satm12

Reputation: 60

Synchronized on Servlet service method

I was reading the Servlet Specification and came across this:

For servlets not implementing the SingleThreadModel interface, if the service method (or methods such as doGet or doPost which are dispatched to the service method of the HttpServlet abstract class) has been defined with the synchronized keyword, the servlet container cannot use the instance pool approach, but must serialize requests through it.

I don't understand why the servlet container cannot use the instance pool approach with a synchronized service method. Doesn't the instance pool contain different instances of the servelet so that every instance will use itself to synchronize the method (not blocking each other)?

From what I understand the the synchronize will be useless in this case but it does not stop the servlet container from using an instance pool.

What am I missing?

Thanks.

Upvotes: 1

Views: 819

Answers (1)

tsolakp
tsolakp

Reputation: 5948

What that sentence is saying is that if you dont implement SingleThreadModel then your Servlet instance wont be pooled at all no matter it it uses synchronization or not. The only reason it mentions synchronization is to warn you that Servlet container wont be using multiple instances of your Servlet per VM to allow it to process multiple requests at the same time.

Here is another missing fragment from the spec:

SRV.2.2 Number of Instances

The servlet declaration which is part of the deployment descriptor of the Web application containing the servlet, as described in Chapter SRV.13, “Deployment Descriptor”, controls how the servlet container provides instances of the servlet. For a servlet not hosted in a distributed environment (the default), the servlet container must use only one instance per servlet declaration. However, for a servlet implementing the SingleThreadModel interface, the servlet container may instantiate multiple instances to handle a heavy request load and serialize requests to a particular instance. Servlet Life Cycle 19 In the case where a servlet was deployed as part of an application marked in the deployment descriptor as distributable, a container may have only one instance per servlet declaration per Java Virtual Machine (JVMTM) 1 . However, if the servlet in a distributable application implements the SingleThreadModel interface, the container may instantiate multiple instances of that servlet in each JVM of the container

Upvotes: 3

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