We found a very bad issue which causes the cache to deadlock and completly block access to some resources.
The problem is related to how cache keys are updated,
currently OS-Cache will mark a cache-key as being 'created/updated' and will block all forthcoming requests to that resource until the first request is completed

we however observed the following behaviour:
- Client Thread 1: GET /upload/problem.pdf (which is 200K)
- Client Thread 1: READ 200 Bytes
- OS-Cache Thread 1 (serving Client Thread 1): create cache entry and block resource /upload/problem.pdf
- Client Thread 1: decide that this may be a PDF, spawn Client Thread 2 to try indexing, wait for Thread 2 to complete
- Client Thread 2: GET /upload/problem.pdf
- Client Thread 2: READ 1000 Bytes
- OS-Cache Thread 2 (serving Client Thread 2): wait for OS-Cache Thread 1 to complete

as a result now no one will bne able to access that resource and we'll have lost 2 threads/sockets.
This issue definitively needs to be fixed, owr solution is as follows:

class: com.opensympony.oscache.base.Cache:

/**
     * Simone: check if the entry is being updated
     *
     * @param key
     * @return
     */
    public boolean isUpdatingEntry(String key) {
        EntryUpdateState updateState = getUpdateState(key);
        if (updateState==null)
            return false;
        synchronized (updateState) {
            if (updateState.isUpdating())
                return true;
            else
                return false;
                
}
    }


class: Filter:

added the following code before starting to cache /acntuall within the try block):
            // avoid blocking when 2 clients
            if (cache.isUpdatingEntry(key)) {
                // 1: try delaying the request to allow the other thread to complete
                try {
Thread.sleep(5000 +(System.currentTimeMillis()%4000) );
                } catch (InterruptedException ie) {
                    // that's ok
                }
                
// 2: is still busy bypass the cache
                if (cache.isUpdatingEntry(key)) {
chain.doFilter(request,response);
return;
                }
            }