Precise time measurement in Java

Question

Java gives access to two method to get the current time: System.nanoTime() and System.currentTimeMillis(). The first one gives a result in nanoseconds,

Answer 1

JNI: Create a simple function to access the Intel RDTSC instruction or the PMCCNTR register of co-processor p15 in ARM.

Pure Java: You can possibly get better values if you are willing to delay until a clock tick. You can spin checking System.nanoTime() until the value changes. If you know for instance that the value of System.nanoTime() changes every 10000 loop iterations on your platform by amount DELTA then the actual event time was finalNanoTime-DELTA*ITERATIONS/10000. You will need to "warm-up" the code before taking actual measurements.

Hack (for profiling, etc, only): If garbage collection is throwing you off you could always measure the time using a high-priority thread running in a second jvm which doesn't create objects. Have it spin incrementing a long in shared memory which you use as a clock.