Hello Daniel, this is good news. I do wonder: is there a plan to make this an intrinsic(+vsyscall on Linux) just like System.currentTimeMillis()?
Because using it for high precision timestamps would only make sense if it is similar lightweight. Greetings Bernd Am Fri, 09 Jan 2015 17:56:28 +0100 schrieb Daniel Fuchs <daniel.fu...@oracle.com>: > Hi, > > Please find below a webrev for: > > 8068730: Increase the precision of the implementation > of java.time.Clock.systemUTC() > https://bugs.openjdk.java.net/browse/JDK-8068730 > > The java.time.Clock.system() method (and variants thereof) are > specified to "obtain a clock that returns the current instant > using best available system clock". However the current > implementation of the clock returned is based on > System.currentTimeMillis() whereas the underlying native clock > used by System.currentTimeMillis() has often a greater precision > than milliseconds (for instance, on Linux, System.currentTimeMillis() > is based on gettimeofday, which offers microseconds precision). > > This patch enhances the implementation of the > java.time.Clock.SystemClock, so that it offer at least the > same precision than the underlying clock available on the system. > > There is no change in the public API. > > http://cr.openjdk.java.net/~dfuchs/webrev_8068730/webrev.00/ > > Some more details on the patch: > > native (hotspot) side: > > - adds a new method to the os class: > os::javaTimeSystemUTC(jlong &seconds, jlong &nanos) > which allows to get the time in the form of a number > of seconds and number of nanoseconds > (see os.hpp and various os_<os>.cpp files) > > - adds a JVM_GetNanoTimeAdjustment method, which takes > an offset (in seconds) as parameter and returns a > nano time adjustment compared to the offset. > Calls os::javaTimeSystemUTC to compute the adjustment > (see jvm.cpp) > > java (jdk) side: > > - adds a native sun.misc.VM.getNanoTimeAdjustment method > (which is bound to JVM_GetNanoTimeAdjustment) > (see VM.java and VM.c) > > - modifies java.time.Clock.SystemClock to call the new > sun.misc.VM.getNanoTimeAdjustment instead of > System.currentTimeMillis. > > - fixes java.util.Formatter - which wasn't expecting > greater than millisecond precision. > > testing: > > - A new test is added to test sun.misc.VM.getNanoTimeAdjustment > In particular it checks the edge cases. > - New tests are added to TestClock_System.java to check for > the increased precision. > There is also a test for the edge cases there. > - Some java.time tests where tripped by the increased precision, > and had to be modified to take that into account > > Note: comparing the new os::javaTimeSystemUTC with os::javaTimeMillis > can help in reviewing the changes. > > best regards, > > -- daniel
