Re : what is the most precise time I can get in JDK?
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 -
Re: Re : what is the most precise time I can get in JDK?
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 Wangweijun.w...@oracle.com À : David Holmesdavid.hol...@oracle.com Cc : core-libs-devcore-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 -
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 -
Re: what is the most precise time I can get in JDK?
On 16/11/2011 6:09 PM, Weijun Wang wrote: 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(). What you have tried is pretty much all you can do. nanoTime is not connected to to the time-of-day. If you need to make a connection then you need to make it and keep it synchronized. David - 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 -
what is the most precise time I can get in JDK?
Hi All 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 Thanks Max
Re: what is the most precise time I can get in JDK?
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 -
