long running application (tail like)

Question

I want to write an tail like app. Now this app, scans a file for changes in the background and fires events in case something changed.

I want to run my application until the user requests to exit it by pressing ctrl + c (working by default). I do not want to create a lot of CPU load just by doing an endless while(true) loop like I'm doing ATM:

try {
        // thread doing the monitoring
        thread.start();

        // forcing the programm not to exit
        while (System.in.available() == 0) {
            Thread.sleep(5000);
        }

    } catch (final IOException e) {
        e.printStackTrace();
    }

Does anyone know a more elegant/the right approach for this?

score 2 · Accepted Answer · answered May 10 '12 at 13:53

2

I'm not sure why you are using a thread in the first place, the 'tail' unix script is simply a while(true) loop with no exit condition. It watches the file and prints changes if any is detected. I think by default it pauses 1 second, so basically:

while(true) {
   // Code goes here. Watch file, System.out.print if it changes

   Thread.sleep(1000);
}

No need for a thread. But to answer the question about the best way to keep your app alive: Simply don't return from the thread's run() method. You don't have to join the thread, the application will stay in the foreground as long as it has one non-daemon running thread.

answered May 10 '12 at 13:53

mprivat

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I thought a while(true) look will cause a lot of unnessesary load to my cpu. – Matthias B May 10 '12 at 14:10
1

That's what the sleep is for. – TaZ May 10 '12 at 14:20
I'll give it a try. I always thougt there is a "better" way :D – Matthias B May 10 '12 at 14:24

Marko Topolnik · Answer 2 · 2012-05-10T14:23:31.503

0

If you want to read the System.in without busy-waiting, that's very easy to achieve. InputStream has blocking semantics so all you need to to is call one of the read methods and it will block until there is input available. If you are scanning text input, I'd advise BufferedReader.readLine. Also, do that on the main thread, no point in starting another one.

edited May 10 '12 at 14:23

answered May 10 '12 at 13:53

Marko Topolnik

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I edited my question, maybe it's more clear now. Why did somebody of you downvote my post? – Matthias B May 10 '12 at 14:16
What do you mean by "somebody of you?" Do you take me personally for a keeper of the entire SO? – Marko Topolnik May 10 '12 at 14:21
Sorry, thought it was you, because you said its unclear what I want. I'm sorry about this imputation! – Matthias B May 10 '12 at 14:23
You should refrain from doing that on SO. If you want to contend a downvote, comment under your question with @downvoter tag. It's not going to notify the downvoter, but at least you're not going to be throwing accusations at people who are actually helping you. There, I upvoted your Q so you don't feel sore about it :) – Marko Topolnik May 10 '12 at 14:25
Thanks, now I now. Next time I will do better! – Matthias B May 10 '12 at 14:28

long running application (tail like)

2 Answers2