08 September 2008

JavaPerformanceTuning points on java system time

Tips July 2008
# System.currentTimeMillis can have resolution times as bad as 60ms on some systems, and in any case resolution is very system dependent. Don't use it to try to reliably measure short times.
# System.nanoTime returns the number of nanoseconds since some arbitrary offset. It is useful for differential time measurements; Its accuracy and precision should never be worse than System.currentTimeMillis; it can deliver accuracy and precision in the microsecond range on many modern systems.
# ThreadMXBean.getCurrentThreadCpuTime offers the possibility of measuring CPU time used by the current thread. But it may not be available, and may have significant overheads. It should be used carefully.
# On Windows, System.nanoTime involves an OS call that executes in microseconds, so it should not be called more than once every 100 microseconds or so to keep the measurement impact under 1 percent.

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