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0 pointshinkley6y ago0 comments

If memory serves, the new one uses an extra object header that points from the old object to the new one during move operations, and any reads of the old object get forwarded to the new one.

I'm pretty sure that would have not performed well without the aggressive prediction logic in modern processors.

Java 1's object accesses always read through an indirect pointer, but that went away in the name of performance, either when Hotspot was introduced, or on the next round of GC impromevents.

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_old_dude_6y ago

They are two new GCs Shenandoah and ZGC.

Indirect pointers or Brooks pointers has it is called were used in Shenandoah v1 to allow an application thread that perform a read to not move the object during the evacuation phase. This strategy has been removed in Shenandoah v2 to have a better throughput so now both read and write by the application move the object during the evacuation phase.

ZGC has never used Brooks pointers.

MaxBarraclough6y ago

I had to look up 'Brooks pointers'. For anyone else in this position, these two blog posts seem a good place to start: https://rkennke.wordpress.com/2013/10/23/shenandoah-gc-brook... , https://blog.plan99.net/modern-garbage-collection-part-2-1c8...

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