[Python-Dev] pymalloc killer

[Kevin Jacobs]

Some wild-ass thoughts:

On Fri, 29 Mar 2002, Tim Peters wrote:
> A nasty subtlety:  if PyMem_NukeIt is called when the GIL isn't held, it's
> going to take a lot of thought to see whether this can be made safe when
> called simultaneously by multiple threads; e.g., the finger can change
> "mid-stream"

Then make multiple thread-specific fingers, which will presumably result in
higher hit rates due to better locality.  To prevent fingers from being
invalidated, do not remove arenas that are deallocated from the tree -- just
mark them inactive.

> then, and, worse, some thread that *does* hold the GIL may
> legitimately cause a new arena to be allocated midstream, mutating the
> address vector during the search.  This may be intractable enough to kill
> the idea of mapping PyMem_XXX to this.

Why not use a smaller (non-global) lock to protect arena modification and
finger flushing?  Ideally, the lock should be cheap for readers (which I
presume will be the vast majority of accesses) and relatively expensive for
writers (which I assume will occur only when arenas are added or
deactivated).

-Kevin

--
Kevin Jacobs
The OPAL Group - Enterprise Systems Architect
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