[PEAK] A few issues and suggestions

[Phillip J. Eby]

At 04:37 PM 11/5/2008 +0200, Sergey Schetinin wrote:
>One more issue:
>
>   File "c:\files\checkouts\trellis\peak\events\stm.py", line 470, 
> in atomically
>     return super(Controller,self).atomically(self._process, func, args, kw)
>   File "c:\files\checkouts\trellis\peak\events\stm.py", line 186, 
> in atomically
>     self.cleanup(*sys.exc_info())
>   File "c:\files\checkouts\trellis\peak\events\stm.py", line 182, 
> in atomically
>     retval = func(*args, **kw)
>   File "c:\files\checkouts\trellis\peak\events\stm.py", line 486, in _process
>     self.run_rule(listener)
>   File "c:\files\checkouts\trellis\peak\events\stm.py", line 364, in run_rule
>     listener.run()
>   File "c:\files\checkouts\trellis\peak\events\trellis.py", line 559, in run
>     raise AssertionError("This should never happen!", self)
>AssertionError: ('This should never happen!', Cell(<bound method
>VPanel._minh of <gui5.models.VPanel object at 0x00C8CBB0>>, 0))
>
>
>
>And the rule for which that happens looks like this:
>
>     @maintain(initially=0)
>     def _minh(self):
>         prev = self._minh
>         if prev == 0 and self.live:
>             return self.height
>         return prev

Unfortunately, the rule itself will give us no clue of what 
happened.  Basically, it looks like for this to have happened, the 
cell had to have been assigned to between the time it was scheduled, 
and the time it was run.  I suspect it could be triggered by a sequence like:

cell A depends on B and C
B depends on C
C triggers a change in B
B sets a value in A

Probably, setting a value should cancel the scheduled rule if it 
doesn't need initialization.  I suggest adding an "else: 
cancel(self)" to the "if self._needs_init:" block in 
Cell.set_value.  If that makes the problem go away, the above 
hypotheses are probably correct.