Sounds interesting, but there is no attachment ?
-Ulf
Am 18.11.2011 20:35, schrieb Jeff Hain:
Hi.
I've had the same need (or desire), and made a ThinTime class for it (attached).
Returned time :
- is not much more inaccurate than System.currentTimeMillis(),
- is always ahead of System.currentTimeMillis(),
- is monotonic (unless System.currentTimeMillis() jumps backward),
- should change way more often than System.currentTimeMillis().
NB: It makes use of "raw" AtomicXXX classes, without cache line padding,
so there is room for optimization here, but maybe you are like me and
prefer to wait on @Contended annotation arrival than plague your code
with unreliable padding magic :)
-Jeff
________________________________
De : Weijun Wang<weijun.w...@oracle.com>
À : David Holmes<david.hol...@oracle.com>
Cc : core-libs-dev<core-libs-dev@openjdk.java.net>
Envoyé le : Mercredi 16 Novembre 2011 9h09
Objet : Re: what is the most precise time I can get in JDK?
Hi Davis
Yes, I know nanoTime() is precise, but how can I get a clock time from
it? I have tried to record a currentTimeMillis() value when the program
starts and then use the elapse of the nanaTime() to get a current time.
This will break if the user adjusts the system clock during the program
execution.
One solution is to keep tracking the changing of both
currentTimeMillis() and nanoTime(). If the change of one has a
difference (say,> 1 sec) from the other one, it means a system clock
change and I can quickly reset my time to currentTimeMillis().
Thanks
Max
On 11/16/2011 03:23 PM, David Holmes wrote:
Hi Max,
On 16/11/2011 2:55 PM, Weijun Wang wrote:
I need a precise time, and is currently using java.util.Date, which knows
about milliseconds, but unfortunately the precision is only 10-15
milliseconds on a Windows.
In fact, I don't really need it to be so correct. My requirements are:
1. It's enough correct, say, at least as correct as Date.
2. It's precise in a relative sense, i.e. it changes fast
3. It should be monotonic, i.e. it grows, unless the user adjusts the
system
clock
There are only two time source available:
1. The time-of-day clock
This is what Date reports and is also what System.currentTimeMillis
reports. It only has millisecond precision. It's rate of update is
dependent on the OS - for Windows that is typically every 10ms or every
15ms depending on version.
2. The high resolution time source
This is what System.nanoTime reports. It has nanosecond precision, but
again depending on the OS it's resolution (update rate) will vary. The
update rate should easily be in the tens of microseconds. It should be
monotonic non-decreasing but it is not connected to the time-of-day
clock (and so should not be affected by any changes therein).
I have an old blog entry on this:
http://blogs.oracle.com/dholmes/entry/inside_the_hotspot_vm_clocks
David
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