when using the filter you might want to cache multiple patterns.
e.g.:
pattern1: /upload/*
pattern2: *.gif

in such a configuration requesting a resource like /upload/test.gif will cause a deed-lock

here is why:
- pattern1 is invoked
- pattern1 holds a monitor telling it's going to cache the resource
- pattern1 tells the filter-chain to produce the content
- pattern2 is invoked
- pattern2 finds the object already being cached
- pattern2 being wait on the monitor
- a dead-lock is born

basically the monitor should avoid quick-flooding by placing multiple parallel requests in a queue, however in this case both the callers come from the same request and thus should now block eachother