Re: big cpu consumption

From:
Tom Anderson <twic@urchin.earth.li>
Newsgroups:
comp.lang.java.programmer
Date:
Mon, 18 Aug 2008 21:25:38 +0100
Message-ID:
<Pine.LNX.4.64.0808182118090.2932@urchin.earth.li>
On Mon, 18 Aug 2008, EJP wrote:

That's what we call a busy-wait


No it's not.


Well, actually it is, although it's waiting for a condition which will
never occur.

, and it is indeed a very good way to waste all your CPU time.


There is no CPU time being used here at all actually. There is
wall-clock time being spent while the read() method blocks. Not the same
thing.


And also not what the OP reported:

"I have a big problem with cpu usage. when i listen microphone to record
what comes, cpu time is consumed apr. 80% everytime which seems
unnecessary."

Clearly, CPU time *is* being used, and this *is* a busy-wait. But, having
read what you read elsewhere in this thread, i realise my diagnosis (based
not on knowledge of the API, but on inference from what the OP wrote, ie
guesswork - my bad!) was misguided. I thought that read() was returning -1
when there wasn't data available, which is not what the documentation
says. I imagine your suggestion of sorting out start() is the right one.

while ((numBytesRead = line.read(data, 0, bufferLengthInBytes)) == -1) {
    try {
        Thread.sleep(t) ;
    }
    catch (InterruptedException e) {
        // can probably ignore this
    }
}

Where t is a duration in milliseconds. This basically means that your
program will wait for a while before trying to read data again. It
won't be consuming CPU while it waits.


Excuse me but this is all nonsense. The read() will return -1 at the end
of the stream. At this point there will *never* be any more data on the
stream.


Fair enough. If the OP's program is busy-waiting for data which will never
come, my approach will still reduce CPU use, though - it makes the
pointless wait far more efficient!

tom

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