[concurrency-interest] DirectByteBuffers and reachabilityFence

Justin Sampson jsampson at guidewire.com
Wed Dec 9 21:54:38 EST 2015

Vitaly Davidovich wrote:

> I've seen happens-before defined as writes happen before reads and
> say nothing about reads before writes or reads before reads. All
> I'm saying is that full clarity is warranted so we don't need to
> have debates like this.

"A set of actions A is happens-before consistent if for all reads r
in A, where W(r) is the write action seen by r, it is not the case
that either hb(r, W(r)) or that there exists a write w in A such
that w.v = r.v and hb(W(r), w) and hb(w, r)."


The prohibition of reads seeing writes that occur later in the
happens-before ordering is the very first clause ("it is not the
case that either hb(r, W(r)) or ...") of the definition of
happens-before consistency.


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