RFR (S) 8031818: Experimental VM flag for enforcing safe object construction (original) (raw)

Remi Forax forax at univ-mlv.fr
Wed Jan 22 00:44:13 PST 2014

On 01/21/2014 11:47 PM, Aleksey Shipilev wrote:

Hi,

Please review the experimental patch for switching the research VM mode which unconditionally emits the memory barrier at the end of constructor: http://cr.openjdk.java.net/~shade/8031818/webrev.00/ https://bugs.openjdk.java.net/browse/JDK-8031818 This would be convenient to have in mainline, because it will also propagate to another arch ports (notably PPC C2 port), and will ease the performance research for the upcoming JMM update. Thanks, -Aleksey.

My mail is a little OT but anyway, Aleksey, I don't understand why the performance are not mostly identical. Correct me if I'm wrong, for TSO architecture, you basically do nothing so no impact. For ARM or PPC, you need a barrier but anyway you need to emit a barrier when you store the class pointer in the header of the object, so it should not perf at all the JIT is able to see that the class pointer is not read in the constructor (if 'this' doesn't escape and no invokevirtual/invokeinterface/instanceof etc).

cheers, Rémi

More information about the hotspot-compiler-dev mailing list