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Java Forum / General / February 2005HP/UX Java 1.3.1.02 date/time differences
Hi! We seem to have differences between the unix system time (coming from an NTP server) and the time our java application has (as it produces timestamps). At the start of the app the time is synchro and after about 2 weeks the time is 20secs ahead of the system time... Does the Java VM calculates the current time by its own (i.e. counting secs from start)? Or should it better get the time (if System.currentTimeMillis() is called) from the host system? Regards, Steffen >We seem to have differences between the unix system time (coming from >an NTP server) and the time our java application has (as it produces >timestamps). >At the start of the app the time is synchro and after about 2 weeks >the time is 20secs ahead of the system time... Keep your machines is sync by having them check in with an NTP server. See http://mindprod.com/jgloss/atomiclock.html PC's have two clocks, an accurate one, and a time of day ticks since midnight that is reset on boot. Modern tick clocks are pretty accurate, but on older machines, they will get out of whack if you don't reboot daily or resync from the clock calendar. Since accessing the tick clock is faster, that's what you normally get from Windows OS. -- Canadian Mind Products, Roedy Green. Coaching, problem solving, economical contract programming. See http://mindprod.com/jgloss/jgloss.html for The Java Glossary. > >We seem to have differences between the unix system time (coming from > >an NTP server) and the time our java application has (as it produces [quoted text clipped - 4 lines] > Keep your machines is sync by having them check in with an NTP server. > See http://mindprod.com/jgloss/atomiclock.html Win XP uses NTP once per week to reset the clock. > PC's have two clocks, an accurate one, and a time of day ticks since > midnight that is reset on boot. Modern tick clocks are pretty [quoted text clipped - 7 lines] > Coaching, problem solving, economical contract programming. > See http://mindprod.com/jgloss/jgloss.html for The Java Glossary. Hi Steffen we have notified the same problem, but with a HP/UX Java 1.4.2 VM. Our timeshift is 5 secs after a couple of weeks. Right at Java VM start we don't see any time shift between System.currentTimeMillis and the system time, just as you noted. Do you have meanwhile an answer to your question, or a workaround? Is this a bug in the Java VM? thank you for your reply Bojan Release notes for HP/Ux Java VM: Since SDK 1.2.2.09 and SDK 1.3.1, there has been a change in the way the HotSpot JVM uses the gettimeofday() system call to obtain date and time information. For performance reasons a new mechanism is used that uses the number of cpu ticks since the application started, to calculate the current time. As a result, changes to the system date or time using date(1), adjtime(2) or time synchronization utilities such as ntp will not be reflected in the date and time that Java returns, until the process is restarted. If your application requires that Java immediately reflects such system time changes, you can use the -XX:+UseGetTimeOfDay option to tell the JVM to use the gettimeofday call instead of the new, lightweight mechanism. However you may notice a drop in performance, Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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