Revert "used ReentrantLock instead of synchronized blocks"

This reverts commit 824ccec79a7c0c3359a24be7d40bb26d2cf3b6c6.
Revert "fix for UDIG-1931 (synchonized access on blackboard HashMap)"

This reverts commit c33431055da8054116a3be455778a550ee595e5b.