[pypy-dev] Questions for Armin

Bengt Richter bokr at oz.net
Sun Jan 19 08:25:52 CET 2003

At 22:40 2003-01-18 -0600, Edward K. Ream wrote:
>Hello Armin,
>> On Fri, Jan 17, 2003 at 01:08:28PM -0600, Edward K. Ream wrote:
>> > 1.  How often and under what circumstances does psyco_compatible get
>> >
>> > My _guess_ is that it gets called once per every invocation of every
>> > "psycotic" function (function optimized by psyco).  Is this correct?
>> No: psyco_compatible() is only called at compile-time.
>> Only when a new, not-already-seen type appears does it follow the
>> "uncommon_case" branch.  This triggers more compilation, i.e. emission of
>> machine code...
>Many thanks for this most interesting and informative reply.  It clears up a
>lot of my questions.  I feel much more free to focus on the big picture.
>> All your comments about Psyco are founded, but you are focusing too much
>> the "back-end" part...
>Yes.  I have been focusing on an "accounting" question: how often does the
>compiler run?  If the compiler starts from scratch every time a program is
>run, then I gather from your example that the compiler will be called once
>for every type of very argument for every executed function _every time the
>program runs_.  Perhaps you are assuming that the gains from compiling will
>be so large that it doesn't matter how often the compiler runs.

Well, if most everything is written in python, with all  the
libraries etc., I  think there still  is some accounting  to
do. I.e.,  library modules  won't change  much after  having
been exercised a bit. Will this keep updating cached info in
.pyc (or maybe  new .pyp)  files? (BTW, IWT  that makes  for
eventual permissions issues,  if it's  shared libraries.  Do
you just get per-use caches, etc.?) IMO there has to be some
way of not rebuilding the world a lot, even if it's fast ;-)

I'm also  picking this  place  to re-introduce  the  related
"checkpointing" idea, namely some  call into a builtin  that
can act  like  a yield  and  save  all the  state  that  the
compiler/psyco etc have worked up. Perhaps some kind of .pyk
for (python checkpoint)  file that could  resume from  where
the checkpoint call  was. I believe  it can be  done if  the
interpreter stack(s) is/are  able to be  encapsulated and  a
little restart info can be stored statically and the machine
stack can unwind totally out of main and the C runtime exit,
so that coming back into C  main everyting can be picked  up

I don't want to belabor it, but just mention it as something
to  consider,  in  case  it   becomes  easy  when  you   are
redesigning the VM and its environment.

Obviously there has to be some restrictions on state, but  I
think if we could wind up with fast-load application  images
in  the  future  because  you  kept  this  in  mind  in  the
beginning, it could be a benefit.

Bengt Richter
BTW[OT], sorry about the justification. Now I can't get it back
without retyping or writing a re-spacing ragged wrapper.

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