On 7 nov. 2012, at 09:10, Keith OHara <k-ohara5...@oco.net> wrote: > On Mon, 05 Nov 2012 21:52:15 -0800, m...@mikesolomon.org > <m...@mikesolomon.org> wrote: > >> On 6 nov. 2012, at 04:51, Keith OHara <k-ohara5...@oco.net> wrote: >> >>> Just to be clear, rest-collision.cc breaks the circular dependency by >>> setting >>> positioning-done := true, >> >> I'm still not sure how this breaks the dependency. If I look up the extent >> of a rest, this will set 'Y-extent to 'calculation-in-progress for the rest. >> Then, when 'Y-extent is read again in F, it will still be >> 'calculation-in-progress. Setting 'positioning-done to #t only prevents >> calc_positioning_done by being called multiple times (say by other rests) - >> it doesn't fill in the 'calculation-in-progress for 'Y-extent. Or am I >> missing something? >> > > Setting 'positioning-done to #t prevents calc_positioning_done() being called > repeatedly for the same rest in an endless cycle; that is, it breaks the > cycle of dependency. >
Yes, here I agree. > If the process begins with a lookup of Y-extent, then I follow what you say > on how the chain of dependencies could lookup the same Y-extent once again, > before reaching the end of the data-dependency chain. The first lookup of > Y-extent sets a trap intended to detect and stop cyclic dependencies, while > the second lookup activates the trap. > Exactly. > In this case there would be no further lookups of Y-extent on the same rest, > so we could consider this a false-positive activation of the trap. It is > probably wisest to keep the simple trap, even if it can have false-positives. > (I argued before that the calculation-in-progress message should be a > warning, not error.) > > Do you have input that generates the "calculation-in-progress encountered..." > message for rests? > No, but I can make it happen fairly easily from the C++ backend. I'll be posting a patch set later in the week where you'll see an exception that covers this case (there are none other like it in the code base). > Maybe you can arrange to have Rest_collision::force_shift_callback_rest() > called before looking up the Y-extent of a rest. > > Or, maybe we should change calc_positioning_done() to call directly > Rest::generic_extent_callback() rather than going through the symbol lookup. > This way, the C code would assume responsibility for preventing endless data > dependency chains. Your earlier suggestion about having > Rest::generic_extent_callback() consistently ignore ledgers should work fine. This is a good idea except that it'd fail for custom rest stencils. It'd be great if we could drum up a generic solution. Cheers, MS _______________________________________________ lilypond-devel mailing list lilypond-devel@gnu.org https://lists.gnu.org/mailman/listinfo/lilypond-devel
