Changed simple synchronization to ReentrantReadWriteLock

[LupusMKW]

Due to 4f33be6 our application does no longer work.

The commit improved the situation with respect to concurrent mutability of the Services array. Previously, it was possible to read the array while it was being modified concurrently.
Unfortunately, it can now happen that Tomcat runs into a deadlock if a starting application attempts to gather information from the Services array (which all our applications do).

The proposed change replaces the simple lock with a ReentrantReaderWriter lock, so that readers can read the Services array and only writers are blocked.

[ChristopherSchultz]

Thank you for this PR, though I was already working on a patch and the unit tests pass, so I'm going to commit my patch instead of yours. I will credit you for the idea in the changelog, however.

I like my patch better than yours primarily because you are placing the call to lock.lock() within the try block, and it should be placed before the try block instead. Also, I use two separate Lock objects instead of calling ReentrantReadWriteLock.writeLock() or .readLock() each time, which makes it easier to read the code to see that the correct lock is being used.

I could just add commits to your PR to make it work, but the work is already done on my end so I'm gonna commit mine.