[Python-Dev] finalization again

[Barry A. Warsaw]

Okay, I had a flash of inspiration on the way home from my gig
tonight.  Of course, I'm also really tired so I'm sure Tim will shoot
this down in his usual witty but humbling way.  I just had to get this
out or I wouldn't sleep tonight.

What if you timestamp instances when you create them?  Then when you
have trash cycles with finalizers, you sort them and finalize in
chronological order.  The nice thing here is that the user can have
complete control over finalization order by controlling object
creation order.

Some random thoughts:

- Finalization order of cyclic finalizable trash is completely
  deterministic.

- Given sufficient resolution of your system clock, you should never
  have two objects with the same timestamp.

- You could reduce the memory footprint by only including a timestamp
  for objects whose classes have __del__'s at instance creation time.
  Sticking an __del__ into your class dynamically would have no effect
  on objects that are already created (and I wouldn't poke you with a
  pointy stick if even post-twiddle instances didn't get
  timestamped).  Thus, such objects would never be finalized -- tough
  luck.

- FIFO order /seems/ more natural to me than FILO, but then I rarely
  create cyclic objects, and almost never use __del__, so this whole
  argument has been somewhat academic to me :).

- The rule seems easy enough to implement, describe, and understand.

I think I came up with a few more points on the drive home, but my
post jam, post lightbulb endorphodrenalin rush is quickly subsiding,
so I leave the rest until tomorrow.

its-simply-a-matter-of-time-ly y'rs,
-Barry