Concurrent.java is a simple test of concurrency of enhancements made to RecordManager to help improve performance and test correctness.
Still remaining is improving BTree and testing thread safety of serialization.
I can't promise locking to be 100% correct. There may be many issues.
Patch for JDBM tree
Updated patch with BTree changes
File Added: jdbm-concurrent.diff
Read test for BTree
File Added: ConcurrentBTreeReadTest.java