@Override
        public void close() {
            Objects.requireNonNull(writeTxnSupplier, "Transaction has already been closed");
            try {
                try {
                    if (writeTxn != null) {
                        writeTxn.close();
                    }
                } finally {
                    writeTxn = null;
                    writeTxnSupplier = null;
                }
            } finally {
                // whatever happens we must release the lock
                if (writeLock != null) {
                    writeLock.unlock();
                    writeLock = null;
                }
            }
        }
Closes the txn and releases the single write lock
stroom-lmdb/src/main/java/stroom/lmdb/LmdbEnv.java