jdk6 missed method sun.misc.Unsafe#copyMemory(Object, long, Object, long, long)

[Andrew Hughes]

----- Original Message -----
> Hello,
> 
> Method sun.misc.Unsafe#copyMemory(Object,long,Object,long,long) is
> used
> in popular Snappy codec implementation [1, 2].
> 
> It's present in openjdk-7 and in late updates of Oracle jdk6. But
> it's
> missed in openjdk-6. Its native implementation is available in jdk6
> hostspot [3], though. As far as I understood, it was removed from
> jdk6
> codebase during preparation to first jdk6 release [4]. I tried to
> restore it in jdk6 sources (left hotspot untouched) and it seems to
> work
> well.
> 
> Can someone clarify, whether it's safe to patch sun.misc.Unsafe and
> use
> this method in jdk6?
> 
> 
> [1] https://github.com/dain/snappy#snappy-in-java
> [2]
> https://github.com/dain/snappy/blob/01f0a37ca40196e08336532ea6d328eb3ed22b67/src/main/java/org/iq80/snappy/UnsafeMemory.java#L101
> [3]
> http://hg.openjdk.java.net/jdk6/jdk6/hotspot/file/cd74fab0a5e3/src/share/vm/prims/unsafe.cpp
> [4]
> http://hg.openjdk.java.net/jdk6/jdk6/jdk/diff/39e8fe7a0af1/src/share/classes/sun/misc/Unsafe.java
> 
> --
> Regards,
> Alex Kasko
> 

It will be in HotSpot because the same HotSpot releases are shared between
6 & 7 (well, they were until 6 stopped at hs20).  Support for features in 8
will likewise appear in 7's HotSpot.

I can't see any reason why it couldn't be backported, but presumably there
was some reason it was removed.
-- 
Andrew :)

Free Java Software Engineer
Red Hat, Inc. (http://www.redhat.com)

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