Filter not returning from chain.doFilter

[benstarr]

I have a filter that is designed to count the number of current requests being handle by Tomcat. The doFilter method looks something like:

public void doFilter(...) throws ... {
 // increment count here

 try {
 chain.doFilter(request, response);
 }
 finally {
 // decrement count here
 }
}

The calls to increment and decrement are synchronized. However, when the server is idle the count does not return to zero. This leads me to believe that either:

a) The chain.doFilter method is never returning for some reason
b) The thread is being terminated in the chain.doFilter method

I can't think of a reason why a) would ever be the case. Does anyone know whether the container (Tomcat 4.1.x) will do b) in any scenario? I can't seem to correlate it to the user hitting the stop button in the browser or being redirected within the chain.doFilter method and I can't see why this would stop the method returning anyway. Any help would be appreciated.

[benstarr]

Obviously the other alternative is that the increment code is throwing an exception but I can't find anything in the logs to indicate this and there is nothing particular in that code that throws any exceptions...

[benstarr]

I have found the problem. I had accidentally synchronized the toString method of my counter object. This was causing some threads to deadlock resulting in the counter not returning to zero.