public void setNumberOfConcurrentRequests(int numberOfConcurrentRequests) {
        // If we reduced the number of concurrent requests and more requests are in-flight
        // than should be, at least log a warning.
        if(numberOfConcurrentRequests < runningRequests.size()) {
            logger.warn("The number of concurrent requests was reduced and currently more requests are in flight.");
        }

        this.numberOfConcurrentRequests = numberOfConcurrentRequests;

        // As we might have increased the number, try to send some more requests.
        processWorkLog();
    }
Important, this is a FIFO Queue for Fairness!
plc4j/spi/src/main/java/org/apache/plc4x/java/spi/transaction/RequestTransactionManager.java