System currentTimeMillis vs System nanoTime

Question

Accuracy Vs  Precision  What I would like to know is whether I should use System currentTimeMillis   or System nanoTime   when updating my object s positions in my game   Their change in movement is directly proportional to the elapsed time since the last call and I want to be as precise as possible   I ve read that there are some serious time-resolution issues between different operating systems  namely that Mac   Linux have an almost 1 ms resolution while Windows has a  50ms resolution      I m primarly running my apps on windows and 50ms resolution seems pretty inaccurate   Are there better options than the two I listed   Any suggestions   comments

User · Answer

System nanoTime   isn t supported in older JVMs   If that is a concern  stick with currentTimeMillis  Regarding accuracy  you are almost correct  On SOME Windows machines  currentTimeMillis   has a resolution of about 10ms  not 50ms   I m not sure why  but some Windows machines are just as accurate as Linux machines   I have used GAGETimer in the past with moderate success

User · Answer

Yes  if such precision is required use System nanoTime    but be aware that you are then requiring a Java 5  JVM   On my XP systems  I see system time reported to at least 100 microseconds 278 nanoseconds using the following code   private void test         System out println  currentTimeMillis    System currentTimeMillis         System out println  nanoTime             System nanoTime         System out println         testNano false                                                                 to sync with currentTimeMillis   timer tick     for int xa 0  xa lt 10  xa              testNano true                    private void testNano boolean shw        long strMS System currentTimeMillis        long strNS System nanoTime        long curMS      while  curMS System currentTimeMillis       strMS            if shw    System out println  Nano     System nanoTime  -strNS                    if shw    System out println  Nano     System nanoTime  -strNS     Milli     curMS-strMS

User · Answer

If you re just looking for extremely precise measurements of elapsed time  use System nanoTime    System currentTimeMillis   will give you the most accurate possible elapsed time in milliseconds since the epoch  but System nanoTime   gives you a nanosecond-precise time  relative to some arbitrary point   From the Java Documentation    public static long nanoTime         Returns the current value of the most precise available system timer  in nanoseconds       This method can only be used to   measure elapsed time and is not   related to any  other notion of system   or wall-clock time  The value returned   represents nanoseconds since some   fixed but arbitrary origin time  perhaps in   the future  so values may be   negative   This method provides   nanosecond precision  but not   necessarily nanosecond accuracy  No   guarantees are made about how   frequently values change  Differences   in successive calls that span greater   than approximately 292 years  263   nanoseconds  will not accurately   compute elapsed time due to numerical   overflow    For example  to measure how long some code takes to execute   long startTime   System nanoTime               the code being measured         long estimatedTime   System nanoTime   - startTime    See also  JavaDoc System nanoTime   and JavaDoc System currentTimeMillis   for more info

User · Answer

If you re just looking for extremely precise measurements of elapsed time  use System nanoTime    System currentTimeMillis   will give you the most accurate possible elapsed time in milliseconds since the epoch  but System nanoTime   gives you a nanosecond-precise time  relative to some arbitrary point   From the Java Documentation    public static long nanoTime         Returns the current value of the most precise available system timer  in nanoseconds       This method can only be used to   measure elapsed time and is not   related to any  other notion of system   or wall-clock time  The value returned   represents nanoseconds since some   fixed but arbitrary origin time  perhaps in   the future  so values may be   negative   This method provides   nanosecond precision  but not   necessarily nanosecond accuracy  No   guarantees are made about how   frequently values change  Differences   in successive calls that span greater   than approximately 292 years  263   nanoseconds  will not accurately   compute elapsed time due to numerical   overflow    For example  to measure how long some code takes to execute   long startTime   System nanoTime               the code being measured         long estimatedTime   System nanoTime   - startTime    See also  JavaDoc System nanoTime   and JavaDoc System currentTimeMillis   for more info

User · Answer

For game graphics  amp  smooth position updates  use System nanoTime   rather than System currentTimeMillis    I switched from currentTimeMillis   to nanoTime   in a game and got a major visual improvement in smoothness of motion   While one millisecond may seem as though it should already be precise  visually it is not  The factors nanoTime   can improve include    accurate pixel positioning below wall-clock resolution ability to anti-alias between pixels  if you want Windows wall-clock inaccuracy clock jitter   inconsistency of when wall-clock actually ticks forward    As other answers suggest  nanoTime does have a performance cost if called repeatedly -- it would be best to call it just once per frame  and use the same value to calculate the entire frame

User · Answer

Update by Arkadiy  I ve observed more correct behavior of System currentTimeMillis   on Windows 7 in Oracle Java 8  The time was returned with 1 millisecond precision  The source code in OpenJDK has not changed  so I do not know what causes the better behavior     David Holmes of Sun posted a blog article a couple years ago that has a very detailed look at the Java timing APIs  in particular System currentTimeMillis   and System nanoTime     when you would want to use which  and how they work internally   Inside the Hotspot VM  Clocks  Timers and Scheduling Events - Part I - Windows  One very interesting aspect of the timer used by Java on Windows for APIs that have a timed wait parameter is that the resolution of the timer can change depending on what other API calls may have been made - system wide  not just in the particular process   He shows an example where using Thread sleep   will cause this resolution change

User · Answer

Update by Arkadiy  I ve observed more correct behavior of System currentTimeMillis   on Windows 7 in Oracle Java 8  The time was returned with 1 millisecond precision  The source code in OpenJDK has not changed  so I do not know what causes the better behavior     David Holmes of Sun posted a blog article a couple years ago that has a very detailed look at the Java timing APIs  in particular System currentTimeMillis   and System nanoTime     when you would want to use which  and how they work internally   Inside the Hotspot VM  Clocks  Timers and Scheduling Events - Part I - Windows  One very interesting aspect of the timer used by Java on Windows for APIs that have a timed wait parameter is that the resolution of the timer can change depending on what other API calls may have been made - system wide  not just in the particular process   He shows an example where using Thread sleep   will cause this resolution change

User · Answer

If you re just looking for extremely precise measurements of elapsed time  use System nanoTime    System currentTimeMillis   will give you the most accurate possible elapsed time in milliseconds since the epoch  but System nanoTime   gives you a nanosecond-precise time  relative to some arbitrary point   From the Java Documentation    public static long nanoTime         Returns the current value of the most precise available system timer  in nanoseconds       This method can only be used to   measure elapsed time and is not   related to any  other notion of system   or wall-clock time  The value returned   represents nanoseconds since some   fixed but arbitrary origin time  perhaps in   the future  so values may be   negative   This method provides   nanosecond precision  but not   necessarily nanosecond accuracy  No   guarantees are made about how   frequently values change  Differences   in successive calls that span greater   than approximately 292 years  263   nanoseconds  will not accurately   compute elapsed time due to numerical   overflow    For example  to measure how long some code takes to execute   long startTime   System nanoTime               the code being measured         long estimatedTime   System nanoTime   - startTime    See also  JavaDoc System nanoTime   and JavaDoc System currentTimeMillis   for more info

User · Answer

Yes  if such precision is required use System nanoTime    but be aware that you are then requiring a Java 5  JVM   On my XP systems  I see system time reported to at least 100 microseconds 278 nanoseconds using the following code   private void test         System out println  currentTimeMillis    System currentTimeMillis         System out println  nanoTime             System nanoTime         System out println         testNano false                                                                 to sync with currentTimeMillis   timer tick     for int xa 0  xa lt 10  xa              testNano true                    private void testNano boolean shw        long strMS System currentTimeMillis        long strNS System nanoTime        long curMS      while  curMS System currentTimeMillis       strMS            if shw    System out println  Nano     System nanoTime  -strNS                    if shw    System out println  Nano     System nanoTime  -strNS     Milli     curMS-strMS

User · Answer

For game graphics  amp  smooth position updates  use System nanoTime   rather than System currentTimeMillis    I switched from currentTimeMillis   to nanoTime   in a game and got a major visual improvement in smoothness of motion   While one millisecond may seem as though it should already be precise  visually it is not  The factors nanoTime   can improve include    accurate pixel positioning below wall-clock resolution ability to anti-alias between pixels  if you want Windows wall-clock inaccuracy clock jitter   inconsistency of when wall-clock actually ticks forward    As other answers suggest  nanoTime does have a performance cost if called repeatedly -- it would be best to call it just once per frame  and use the same value to calculate the entire frame

User · Answer

System nanoTime   isn t supported in older JVMs   If that is a concern  stick with currentTimeMillis  Regarding accuracy  you are almost correct  On SOME Windows machines  currentTimeMillis   has a resolution of about 10ms  not 50ms   I m not sure why  but some Windows machines are just as accurate as Linux machines   I have used GAGETimer in the past with moderate success

User · Answer

one thing here is the inconsistency of the nanoTime method it does not give very consistent values for the same input currentTimeMillis does much better in terms of performance and consistency and also  though not as precise as nanoTime has a lower margin of error and therefore more accuracy in its value  i would therefore suggest that you use currentTimeMillis

User · Answer

Since no one else has mentioned this     It is not safe to compare the results of System nanoTime   calls between different threads  Even if the events of the threads happen in a predictable order  the difference in nanoseconds can be positive or negative   System currentTimeMillis   is safe for use between threads

User · Answer

System currentTimeMillis   is not safe for elapsed time because this method is sensitive to the system realtime clock changes of the system   You should use System nanoTime  Please refer to Java System help   About nanoTime method         This method provides nanosecond precision  but not necessarily   nanosecond resolution  that is  how frequently the value changes  - no   guarantees are made except that the resolution is at least as good as   that of currentTimeMillis       If you use System currentTimeMillis   your elapsed time can be negative  Back  lt -- to the future

User · Answer

Update by Arkadiy  I ve observed more correct behavior of System currentTimeMillis   on Windows 7 in Oracle Java 8  The time was returned with 1 millisecond precision  The source code in OpenJDK has not changed  so I do not know what causes the better behavior     David Holmes of Sun posted a blog article a couple years ago that has a very detailed look at the Java timing APIs  in particular System currentTimeMillis   and System nanoTime     when you would want to use which  and how they work internally   Inside the Hotspot VM  Clocks  Timers and Scheduling Events - Part I - Windows  One very interesting aspect of the timer used by Java on Windows for APIs that have a timed wait parameter is that the resolution of the timer can change depending on what other API calls may have been made - system wide  not just in the particular process   He shows an example where using Thread sleep   will cause this resolution change

User · Answer

System nanoTime   isn t supported in older JVMs   If that is a concern  stick with currentTimeMillis  Regarding accuracy  you are almost correct  On SOME Windows machines  currentTimeMillis   has a resolution of about 10ms  not 50ms   I m not sure why  but some Windows machines are just as accurate as Linux machines   I have used GAGETimer in the past with moderate success

User · Answer

If you re just looking for extremely precise measurements of elapsed time  use System nanoTime    System currentTimeMillis   will give you the most accurate possible elapsed time in milliseconds since the epoch  but System nanoTime   gives you a nanosecond-precise time  relative to some arbitrary point   From the Java Documentation    public static long nanoTime         Returns the current value of the most precise available system timer  in nanoseconds       This method can only be used to   measure elapsed time and is not   related to any  other notion of system   or wall-clock time  The value returned   represents nanoseconds since some   fixed but arbitrary origin time  perhaps in   the future  so values may be   negative   This method provides   nanosecond precision  but not   necessarily nanosecond accuracy  No   guarantees are made about how   frequently values change  Differences   in successive calls that span greater   than approximately 292 years  263   nanoseconds  will not accurately   compute elapsed time due to numerical   overflow    For example  to measure how long some code takes to execute   long startTime   System nanoTime               the code being measured         long estimatedTime   System nanoTime   - startTime    See also  JavaDoc System nanoTime   and JavaDoc System currentTimeMillis   for more info

User · Answer

I ve had good experience with nanotime   It provides wall-clock time as two longs  seconds since the epoch and nanoseconds within that second   using a JNI library   It s available with the JNI part precompiled for both Windows and Linux

User · Answer

System currentTimeMillis   is not safe for elapsed time because this method is sensitive to the system realtime clock changes of the system   You should use System nanoTime  Please refer to Java System help   About nanoTime method         This method provides nanosecond precision  but not necessarily   nanosecond resolution  that is  how frequently the value changes  - no   guarantees are made except that the resolution is at least as good as   that of currentTimeMillis       If you use System currentTimeMillis   your elapsed time can be negative  Back  lt -- to the future

User · Answer

I ve had good experience with nanotime   It provides wall-clock time as two longs  seconds since the epoch and nanoseconds within that second   using a JNI library   It s available with the JNI part precompiled for both Windows and Linux

User · Answer

Since no one else has mentioned this     It is not safe to compare the results of System nanoTime   calls between different threads  Even if the events of the threads happen in a predictable order  the difference in nanoseconds can be positive or negative   System currentTimeMillis   is safe for use between threads

User · Answer

one thing here is the inconsistency of the nanoTime method it does not give very consistent values for the same input currentTimeMillis does much better in terms of performance and consistency and also  though not as precise as nanoTime has a lower margin of error and therefore more accuracy in its value  i would therefore suggest that you use currentTimeMillis

User · Answer

System nanoTime   isn t supported in older JVMs   If that is a concern  stick with currentTimeMillis  Regarding accuracy  you are almost correct  On SOME Windows machines  currentTimeMillis   has a resolution of about 10ms  not 50ms   I m not sure why  but some Windows machines are just as accurate as Linux machines   I have used GAGETimer in the past with moderate success

User · Answer

Update by Arkadiy  I ve observed more correct behavior of System currentTimeMillis   on Windows 7 in Oracle Java 8  The time was returned with 1 millisecond precision  The source code in OpenJDK has not changed  so I do not know what causes the better behavior     David Holmes of Sun posted a blog article a couple years ago that has a very detailed look at the Java timing APIs  in particular System currentTimeMillis   and System nanoTime     when you would want to use which  and how they work internally   Inside the Hotspot VM  Clocks  Timers and Scheduling Events - Part I - Windows  One very interesting aspect of the timer used by Java on Windows for APIs that have a timed wait parameter is that the resolution of the timer can change depending on what other API calls may have been made - system wide  not just in the particular process   He shows an example where using Thread sleep   will cause this resolution change

User · Answer

As others have said  currentTimeMillis is clock time  which changes due to daylight saving time  not  daylight saving  amp  time zone are unrelated to currentTimeMillis  the rest is true   users changing the time settings  leap seconds  and internet time sync  If your app depends on monotonically increasing elapsed time values  you might prefer nanoTime instead  You might think that the players won t be fiddling with the time settings during game play  and maybe you d be right  But don t underestimate the disruption due to internet time sync  or perhaps remote desktop users  The nanoTime API is immune to this kind of disruption  If you want to use clock time  but avoid discontinuities due to internet time sync  you might consider an NTP client such as Meinberg  which  quot tunes quot  the clock rate to zero it in  instead of just resetting the clock periodically  I speak from personal experience  In a weather application that I developed  I was getting randomly occurring wind speed spikes  It took a while for me to realize that my timebase was being disrupted by the behavior of clock time on a typical PC  All my problems disappeared when I started using nanoTime  Consistency  monotonicity  was more important to my application than raw precision or absolute accuracy

User · Answer

As others have said  currentTimeMillis is clock time  which changes due to daylight saving time  not  daylight saving  amp  time zone are unrelated to currentTimeMillis  the rest is true   users changing the time settings  leap seconds  and internet time sync  If your app depends on monotonically increasing elapsed time values  you might prefer nanoTime instead  You might think that the players won t be fiddling with the time settings during game play  and maybe you d be right  But don t underestimate the disruption due to internet time sync  or perhaps remote desktop users  The nanoTime API is immune to this kind of disruption  If you want to use clock time  but avoid discontinuities due to internet time sync  you might consider an NTP client such as Meinberg  which  quot tunes quot  the clock rate to zero it in  instead of just resetting the clock periodically  I speak from personal experience  In a weather application that I developed  I was getting randomly occurring wind speed spikes  It took a while for me to realize that my timebase was being disrupted by the behavior of clock time on a typical PC  All my problems disappeared when I started using nanoTime  Consistency  monotonicity  was more important to my application than raw precision or absolute accuracy

User · Answer

Yes  if such precision is required use System nanoTime    but be aware that you are then requiring a Java 5  JVM   On my XP systems  I see system time reported to at least 100 microseconds 278 nanoseconds using the following code   private void test         System out println  currentTimeMillis    System currentTimeMillis         System out println  nanoTime             System nanoTime         System out println         testNano false                                                                 to sync with currentTimeMillis   timer tick     for int xa 0  xa lt 10  xa              testNano true                    private void testNano boolean shw        long strMS System currentTimeMillis        long strNS System nanoTime        long curMS      while  curMS System currentTimeMillis       strMS            if shw    System out println  Nano     System nanoTime  -strNS                    if shw    System out println  Nano     System nanoTime  -strNS     Milli     curMS-strMS

User · Answer

Yes  if such precision is required use System nanoTime    but be aware that you are then requiring a Java 5  JVM   On my XP systems  I see system time reported to at least 100 microseconds 278 nanoseconds using the following code   private void test         System out println  currentTimeMillis    System currentTimeMillis         System out println  nanoTime             System nanoTime         System out println         testNano false                                                                 to sync with currentTimeMillis   timer tick     for int xa 0  xa lt 10  xa              testNano true                    private void testNano boolean shw        long strMS System currentTimeMillis        long strNS System nanoTime        long curMS      while  curMS System currentTimeMillis       strMS            if shw    System out println  Nano     System nanoTime  -strNS                    if shw    System out println  Nano     System nanoTime  -strNS     Milli     curMS-strMS

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