RFR JDK-7143928 : (coll) Optimize for Empty ArrayList and HashMap (original) (raw)

Laurent Bourgès bourges.laurent at gmail.com
Tue Apr 2 07:27:01 UTC 2013

---

604 Arrays.fill(elementData, newSize, size, null); In performance-critical code I would avoid Arrays.fill because it adds a bit of overhead (unless it's intrinsified, which I don't think it is).

Last week, I sent few benchmarks I did on array cleaning (zero fill) comparing Arrays.fill, System.arraycopy, Unsafe.setMemory ... Arrays.fill is the winner (always faster than arraycopy which use native code) by 10 - 20% ! I suspect aggressive hotspot optimizations (native code ?) because I agree Arrays.fill looks like a stupid for-loop !

Does somebody have clues explaining the Arrays.fill performance ?

Is there an alternative way to clear an array giving the best possible performance (like c memset) ? it could be useful to have in JDK a native array fill implementation (System.fill ?) if it gives better performance.

Laurent

More information about the core-libs-dev mailing list