Comments on: Measuring Execution Time in Nanoseconds in Java http://www.robertpeaslee.com/index.php/measuring-execution-time-in-nanoseconds-in-java/ Tales of rugged geek adventures, complete with traps. Sun, 22 Aug 2010 21:18:55 -0400 http://wordpress.org/?v=2.8.3 hourly 1 By: peasleer http://www.robertpeaslee.com/index.php/measuring-execution-time-in-nanoseconds-in-java/comment-page-1/#comment-394 peasleer Wed, 11 Feb 2009 03:58:08 +0000 http://www.robertpeaslee.com/index.php/measuring-execution-time-in-nanoseconds-in-java/#comment-394 Good tips, thanks for sharing. Yes, for the record, I was using them responsibly (difference of times only, no comparisons, and I was aware that their precision was limited by the most precise clock available). I hadn't read the bug report though, which is also good information to have. Thanks again Dave :) Good tips, thanks for sharing. Yes, for the record, I was using them responsibly (difference of times only, no comparisons, and I was aware that their precision was limited by the most precise clock available). I hadn’t read the bug report though, which is also good information to have. Thanks again Dave :)

]]> By: David Brenner http://www.robertpeaslee.com/index.php/measuring-execution-time-in-nanoseconds-in-java/comment-page-1/#comment-393 David Brenner Tue, 10 Feb 2009 19:46:49 +0000 http://www.robertpeaslee.com/index.php/measuring-execution-time-in-nanoseconds-in-java/#comment-393 Though I'm sure you're using this method responsibly, it is important to note the inherent issues with using such a function to measure time. This bug report, specifically the Sun Developer's evaluation, addresses the most important issues (quoted from: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6519418): - only use nanoTime values to compare against other nanoTime values obtained from within the same VM - resolution (ie the smallest observable update) is dependent on OS and hardware platform but is never worse than currentTimeMillis(). I don't think giving examples is appropriate, but something like "on an operating system with good hardware support a resolution on the order of tens of microseconds is not uncommon" I also think it is worth pointing out that to compare two nanoTime values, long t0 = System.nanoTime(); ... long t1 = System.nanoTime(); one should not do t0 < t1 but instead do t1 - t0 < 0 because of overflow Though I’m sure you’re using this method responsibly, it is important to note the inherent issues with using such a function to measure time. This bug report, specifically the Sun Developer’s evaluation, addresses the most important issues (quoted from: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6519418):

- only use nanoTime values to compare against other nanoTime values obtained from within the same VM
- resolution (ie the smallest observable update) is dependent on OS and hardware platform but is never worse than currentTimeMillis(). I don’t think giving examples is appropriate, but something like “on an operating system with good hardware support a resolution on the order of tens of microseconds is not uncommon”

I also think it is worth pointing out that to compare two nanoTime values,
long t0 = System.nanoTime();
…
long t1 = System.nanoTime();

one should not do
t0 < t1
but instead do
t1 – t0 < 0
because of overflow

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