is abstract class instance variable in servlet container - thread-safe

[Amy Saari]

Hi All

I need some help if you have a minute. We have an app in production that's behaving poorly. We know we have a NOT thread safe condition where two threads running through the same servlet are looking at the same value in an instance variable (userName in the example below). So, for example, two threads in the class first are looking at a single copy of userName.

But what about this - can one thread in first and one thread in second be looking at the same instance of userName? if baseclass is abstract, then are there two instances of userName? one when new is called for class first and one when new is called for class second by the servlet container? know what i mean?

Here's some simple pseudo code to illustrate :

    
class baseclass extends Action // struts Action extends servlet so this is a servlet

	String userName;

	execute () {
		userName = some_value_take_off_request;
		domyexecute();
	}

	String getUserName() {
		return userName;
	}

	abstract domyexecute() {}
}

class first extends baseclass 

	domyexecute() {

		String i_see_this_user_name = getUserName();
	}
}

class second extends baseclass 

	domyexcute() {
	
		String i_see_this_user_name = getUserName();
	}
}

thanks for any thoughts,
amy

[Bear Bibeault]

Please be sure to ask Struts questions in the Struts forum. I have moved this post there for you.

[Bear Bibeault]

If the class is a servlet there will be only one instance shared across all threads and there will be trouble. Write servlets in a thread-safe manner always.

[Amy Saari]

Hi Bear,

I wish you had not moved this to Struts - it doesn't have anything to do with Struts (I should have just left the Action off and put in HttpServlet). Can you / would you move it back perhaps?

We know it's not thread safe. The question is this:

If two classes extend an abstract class that extends HttpServlet - how many instance of an instance variable in the abstract class exist? One or two?

Thanks,
Amy

[Bear Bibeault]

There will be one instance of the variable per instance of the class. The fact that it was declared in an abstract superclass is moot.

[David Newton]

Which version of Struts are you using where Action extends HttpServlet?

[shivendra tripathi]

Hi Amy,
Just to correct you on your thoughts,
ActionServet is the only action which is servlet among all the action classes struts provide.