On Wed, Apr 3, 2013 at 1:10 PM, David Bruant <[email protected]> wrote:
> Le 03/04/2013 21:18, Mark S. Miller a écrit : > > > Do languages which added WeakRefs have a form of revokable reference >> too? What difference would it make? >> > > E has both. In practice, my sense is that their use cases are disjoint, > and that both are needed. > > Do you have examples of use? May be links to E code. > > In what way is the GC-notification mechanism really necessary? (that's the > part that I'm personally annoyed with most). > I would be much less bothered if weakrefs were in essence revocable > references for which only the GC has the revoke function (called on GC of > the underlying target). > It seems it would already solve the use cases exposed on the list which > (my summary) Kevin expressed as "A core part of the problem here is that > the distinction between an 'important' reference - one that must keep an > object alive - and an 'incidental' reference, that only need exist as long > as it target does" > > Whatever final form is chosen (and even if weakrefs are only for ES7), > would it make sense to unify what a revoked proxy and a dead weakref look > like? > Both look very close in what they are. > The main use of weakrefs in E is indeed related to proxies, but not in the way you may expect. Weakrefs are used to implement CapTP's distributed acyclic garbage collector. An E remote-reference-proxy is used as the local representative of a remote object. Though such E proxies are more like Q/ES7 promises than like ES6 proxies. A weakref is used to determine when there is no longer any local need for a reference to that remote object. When this is detected, the local vat sends a message (GCExportOp and GCAnswerOP at <http://erights.org/elib/distrib/captp/DeliverOp.html#step9>) to the remote vat so the remote vat can clean up its corresponding incoming tables. A captp-like protocol for distributed Q should make use of the same technique, but won't be able to until we add weakrefs to ES7. Until then, Q will leak a tremendous amount of distributed acyclic cross-vat garbage. > > > David > -- Cheers, --MarkM
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