Am 20.03.2019 um 18:02 hat Alberto Garcia geschrieben: > On Wed 20 Mar 2019 10:16:10 AM CET, Kevin Wolf wrote: > >> Oh, I see. Let's use a shorter chain for simplicity: > >> > >> A <- B <- C <- D <- E > > > > Written from right to left, i.e. E being the base and A the top layer? > > We usually write things the other write round, I hope this doesn't get > > too confusing later. > > Oh my... yes, of course you're right, I should have written it the other > way around: > > E <- D <- C <- B <- A > > >> 1) If we stream first from E to C we add a filter F: > >> > >> A <- B <- F <- C <- D <- E > > ( which should have been written E <- D <- C <- F <- B <- A ) > > >> Now we can't stream from C to A because F is on the way, and the F-C > >> link is frozen. > > > > Why is a frozen link a problem? The streaming operation isn't going to > > change this link, it just copies data from the subchain (including F > > and C) to A. This is not something that a frozen link should prevent. > > Not the operation itself, but the first thing that block-stream does is > freeze the chain from top (A) to base (C), so this would fail if there's > already a frozen link on the way (C <- F on this case?).
Oh, I see. I think this is why I suggested a counter originally instead of a bool. > > So it seems frozen links allow the wrong case, but block the correct > > one? :-( > > Yes, we probably need to rethink this scenario a bit. But yes, even with a counter, the other problem would still remain (that the first job can't remove the filter on completion because the second one has frozen its link to the filter). I don't think that's a case we want to just forbid because nobody needs this anyway. It's a sign of a more fundamental problem in our design, and I'm sure it will bite us in other places, too. Kevin