Re: Simultaneous destructors

Benjamin Smedberg wrote:
> On 11/9/09 6:36 PM, Chris Jones wrote:
> 
>>> Um, that /is/ the additional complexity :)   Yes, it sounds like
>>> nothing much in
>>> theory, but it's certainly going to be more work, and might be subtle
>>> (we
>>> currently report to listeners when OnDataAvailable is fired:  would we
>>> consolidate the notifications, too?  Firebug might get less accurate
>>> info about
>>> network activity this way, for instance).
>>>
>> I can't really comment on this because know very little about Necko
>> code.  bsmedberg?
> 
> It seems desirable to me that we do not require acknowledging every message:
> when the channel has data available, it sends that data along and doesn't
> cache it.
> 

Hmm, OK.  From my limited perspective of not knowing necko code, I still 
think that the burden of queueing DataAvailable() favors well against 
relaxing IPDL checks.  But if we really want them to be immediately 
forwarded, we'll need either |discard| or divergent state, see below.

> I slightly prefer the divergent-path approach rather than the discard
> approach, for one main reason: it means that we don't have to implement
> special handling for actors which have already been "destructed" but are
> still receiving messages.
> 

You mean for stateless protocols?  We don't need this special handling 
for necko channels, the destruction sequence isn't racy with both 
explicit ACK and |discard|.

> I don't think my opinion is strong enough to *insist* on the divergent-path
> approach, though. If we do go with the discard-bad-messages approach, I'd
> like a very solid approach torwards zombie actor IDs.
> 

Divergent state doesn't help inherently racy protocols, because by 
definition those are stateless protocols.  I haven't fully worked out 
the details of keep-alive for stateless protocols, but the basic idea 
would be to keep the actor alive on the side(s) sending __delete__ until 
the other side ACKs the delete, regardless of async/sync/RPC __delete__. 
  (The ACK is the part I haven't fully worked out.)

Cheers,
Chris