While 循环中的 Thread.sleep()

Question

There is a producer keeps generating files and put them into a special path. The consumer is a using WatchService to monitor the path and pick up any new generated files to work. Usually, the consumer's speed is slower than producer. In rare case, if the consumer finishes all the existing tasks and there is nothing new in the path yet, the consumer needs to hold on for a while.

while(true) {
    // do something...
    if(condition) {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            // handler
        }
    }
}

IDE is complaining that calling to Thread.sleep() in a while loop are indicative of "busy-waiting". Busy-waiting is often inefficient, and may result in unexpected deadlocks as busy-waiting threads do not release locked resources calling to Thread.sleep() in a while loop are indicative of "busy-waiting". Busy-waiting is often inefficient, and may result in unexpected deadlocks as busy-waiting threads do not release locked resources . Ignore this IDE warning will be my last option.

How could I change my code to avoid the above warning architecture wise?

(It seems a scheduled thread pool won't meet my requirement. Please correct me if I'm wrong.)

Thanks for your comments and answers. Buffer events from WatchService to a blocking queue will work.

Answer 1

I completely agree with the IDE. If you use Thread.sleep() you are wrong, most of the time. If you don't know why, then you are wrong all of the time. Yeah I know, it's a strong statement, but in my opinion it should always been kept in mind: in the best case "wrong" means "sub-optimal", in worst cases "wrong" can mean "bad architecture".

In your case, a solution is to use a blocking queue that sends consumer to sleep when the queue is empty and wakes up sleeping consumers when some element arrives.

By the way, I also believe you have the same issue when the queue is full: you may want to pause the producer.

Answer 2

Using Thread.sleep in a real time application is not recommended at all. For your requirement it is recommended to use a scheduler to check up on the path once in a while based on the your application traffic. Any cron job would also help.