Re: The Case of the Disappearing Event

[Roger M. Burkhart]

Manor Askenazi reports:

> I think I've stumbled on a reasonably stealthy bug in
> the Swarm scheduling mechanism. My apologies if this
> bug has already been reported - I'm taking the chance
> of repeating a previous report because the bug is
> quite treacherous and will cause programs to misbehave
> in truly scary and unpredictable ways (basically events
> will start disappearing from your schedule).

This is a known bug -- dynamic update of a schedule from anywhere but
within the schedule actually executing will not automatically reschedule
a schedule already pending within a swarm to execute at a more immediately
pending time.  As best as I recall the bug was most recently summarized in:

  http://www.santafe.edu/projects/swarm/archive/list-archive.9702/0270.html

The fix needs more than just some sort of safe index on the updated,
inactive schedule; it needs a custom handler that will reposition the
pending schedule if it is affected by the time of the new action.  The
complications have so far left this bug in the status of a known restriction
on dynamically updated schedules: generally speaking, you should not use one
schedule to update actions in another, independently merged schedule if
the updates are occurring at immediately upcoming times.  (This, of course,
is when updates are often most likely to be occurring.)  The workaround is
to consolidate the dynamic parts of the schedule into one common schedule
and make that self-updating.  With other recent fixes on AutoDrop cleanup
of dynamic schedules there are enough important fixes in the activity
library that I hope we can get them into a release relatively soon.

Roger


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