private void endRequest(RequestTransaction transaction) {
        if (!runningRequests.contains(transaction)) {
            throw new IllegalArgumentException("Unknown Transaction or Transaction already finished!");
        }
        runningRequests.remove(transaction);
        // Process the work-log, a slot should be free now
        processWorkLog();
    }
Important, this is a FIFO Queue for Fairness!
plc4j/spi/src/main/java/org/apache/plc4x/java/spi/transaction/RequestTransactionManager.java