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.
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.
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?
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.
line 249 of rest.cc [...]
SCM m = brew_internal_stencil (me, false);
and then run make check.
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