[concurrency-interest] Garbage First vs a counting collector

Florian Weimer fw at deneb.enyo.de
Thu Mar 26 17:20:54 EDT 2009


* Jeremy Manson:

> 3) In the case where you are writing to a region you haven't already
> written, it is 2) plus a memory write to record the fact that you are
> writing to another region.

> Even 3) is orders of magnitude cheaper than a CAS.  I'm not sure how
> expensive 4) is, but it doesn't happen all that often.

Depends on the CAS implementation.  CAS (and presumably atomic
increment/decrement on x86) on non-shared cache lines can be made
quite cheap.

One thing to consider is that reference counting only solves the
problem of reachability (ignoring cycles).  It does not help with
fragmentation.


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