presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/util/PrioritizedFifoExecutor.java/PrioritizedFifoExecutor/PrioritizedFifoExecutor
class PrioritizedFifoExecutor:    public PrioritizedFifoExecutor(ExecutorService coreExecutor, int maxThreads, Comparator<T> taskComparator)
    {
        checkArgument(maxThreads > 0, "maxThreads must be greater than zero");

        this.taskComparator = requireNonNull(taskComparator, "taskComparator is null");
        this.executorService = requireNonNull(coreExecutor, "coreExecutor is null");
        this.maxThreads = maxThreads;
        this.queue = new PriorityBlockingQueue<>(maxThreads);
    }