On 17/11/2016 10:00 AM, Peter Levart wrote:
Hi David,
On 11/17/2016 12:35 AM, David Holmes wrote:
Why are we insisting in specifying when it is guaranteed for a Reference
object to *not* be enqueued. This is not very helpful.
I disagree. The whole point of the statement was to make it clear that
for a referent to be enqueued the referee reference type must itself
remain reachable. The problem with the statement was that it could be
misconstrued as indicating when a referent _must_ not be enqueued.
The original text is correct: "If a registered reference becomes
unreachable itself, then it will never be enqueued".
And we must actually read it as "then the reference _must_ not be
enququed".
You are presuming the reader understands precisely what "becomes
unreachable" means. It does not mean "I looked at the source code and at
this point the reference is unused therefore it is unreachable and
therefore the referent must never be enqueued". It means that the VM
detected that the reference was unreachable. Hence the clarification.
David
The transitioning of reachability from unreachable to strongly reachable
is not allowed. If a registered reference becomes unreachable then it
_must_ not be enqueued as enqueueing would transition it to strongly
reachable from unreachable and break the spec.
Regards, Peter
A more helpful information for a programmer would be to specify when a
Reference object is guaranteed to *be* enqueued. Guarantee is given only
if the Reference object is kept strongly reachable. If it ceases to be
strongly reachable, it may never be enqueued, but it is not guaranteed
that it will not be enqueued either.
So this is still my favorite:
"If a registered reference ceases to be strongly reachable for any
period of time, it may become unreachable and never be enqueued. In
order to guarantee for a registered reference to be enqueued, it must be
kept strongly reachable at all times."
That seems redundant to me. Given the reachability definitions it
reduces to "If a registered reference becomes unreachable it may never
be enqueued."
David
