presto-raptor-legacy/src/main/java/io/prestosql/plugin/raptor/legacy/util/PrioritizedFifoExecutor.java/PrioritizedFifoExecutor/executeOrMerge
class PrioritizedFifoExecutor:    private void executeOrMerge()
    {
        int size = queueSize.incrementAndGet();
        if (size > maxThreads) {
            return;
        }
        do {
            try {
                queue.poll().run();
            }
            catch (Throwable e) {
                log.error(e, "Task failed");
            }
        }
        while (queueSize.getAndDecrement() > maxThreads);
    }