could not acquire lock

[ajanz]

sometimes i got following error message

Caused by java.lang.IllegalStateException with message: "could not acquire lock on @Synchronized component: MyBean"

code is

@Stateful
@Name("MyBean")
@Scope(value = ScopeType.SESSION)
public class MyClass implements MyBean{

what is the problem? what can i do?

[lvdberg]

Sascha,

could you provide some more information. It seems that you want to do something with MyBean on a session level. The reason you want a lock is that because of a using different winodws/frames or ajax requests?

Leo

[sherkan777]

Sometimes I get same exception mostly on ajax requests to my SFSB.

I've resolvet this by adding synchronisation to bean class.

@Name("myBeanAction")
@Scope(ScopeType.SESSION)
@Synchronized(timeout=10000)

[lvdberg]

Although the Seam documentation states that aceesing session scoped components are protected from concurerent access, I've found that adding Ajax requests sometimes makes it a bit more complex than you think.

You should try to solve this first at the source;  meaning add a queue to your pages and if that not sufficient or doesn't work, start synchronizing your beans. Especially run-time errors in synchronised beans can give you a lot of headaches (I found that out myself....)

This is what I have in every page with forms/partial updates/rich components

<a4j:queue requestDelay="500" sizeExceededBehavior="dropNew"
               ignoreDupResponce="true" size="10" id="inputQueue" name="inputQueue" timeout="10000" /> 

All a4j:support tags, push etc. refer to this queue. Works for me !

Leo

[sherkan777]

Yes, this is right idea, also for

 a4j:commandButton/a4j:form

etc., try to add

queue="queueName"

.

Use same queue name for each request to this one SFSB, but this exception can be thrown in pure Seam ajax request for js/Seam remoting.

What about then? Only way is to catch concurrent requests by adding @Synchronised.

see this:

However, you can force a serialized threading model on any session bean or JavaBean component by adding the @Synchronized annotation.

This concurrency model means that AJAX clients can safely use volatile session and conversational state, without the need for any special work on the part of the developer.

[lvdberg]

Hi Sherkan,

Off course you should add @Synchronized when you're using Seam remoting, but synchronizing your ajax page requests with a queue saves you a lot of additional problems. The browser is not really a multi-threding wonder and I personally find debugging client side requests not the most exiting part of my job. ;-)