Brett, I have not followed everything here but I have no problem with tweaks at this level as long as you are happy with it.
--Guido (mobile) On Sep 3, 2016 5:39 PM, "Brett Cannon" <br...@python.org> wrote: > > > On Sat, 3 Sep 2016 at 17:27 Yury Selivanov <yselivanov...@gmail.com> > wrote: > >> >> On 2016-09-03 5:19 PM, Brett Cannon wrote: >> > >> > >> > On Sat, 3 Sep 2016 at 16:43 Yury Selivanov <yselivanov...@gmail.com >> > <mailto:yselivanov...@gmail.com>> wrote: >> > >> > >> > >> > On 2016-09-03 4:15 PM, Christian Heimes wrote: >> > > On 2016-09-04 00:03, Yury Selivanov wrote: >> > >> >> > >> On 2016-09-03 12:27 PM, Brett Cannon wrote: >> > >>> Below is the `co_extra` section of PEP 523 with the update >> > saying that >> > >>> users are expected to put a tuple in the field for easier >> > simultaneous >> > >>> use of the field. >> > >>> >> > >>> Since the `co_extra` discussions do not affect CPython itself >> I'm >> > >>> planning on landing the changes stemming from the PEP probably >> > on Monday. >> > >> Tuples are immutable. If you have multiple co_extra users then >> > they >> > >> will have to either mutate tuple (which isn't always possible, >> for >> > >> instance, you can't increase size), or to replace it with >> > another tuple. >> > >> >> > >> Creating lists is a bit more expensive, but item access speed >> > should be >> > >> in the same ballpark. >> > >> >> > >> Another question -- sorry if this was discussed before -- why >> > do we want >> > >> a PyObject* there at all? I.e. why don't we create a dedicated >> > struct >> > >> CoExtraContainer to manage the stuff in co_extra? My >> > understanding is >> > >> that the users of co_extra are C-level python optimizers and >> > profilers, >> > >> which don't need the overhead of CPython API. >> > >> > >> > As Chris pointed out in another email, the overhead is only in the >> > allocation, not the iteration/access if you use the PyTuple macros to >> > get the size and index into the tuple the overhead is negligible. >> >> Yes, my point was that it's as cheap to use a list as a tuple for >> co_extra. If we decide to store PyObject in co_extra. >> >> > >> >> > >> This way my work to add an extra caching layer (which I'm very >> much >> > >> willing to continue to work on) wouldn't require another set of >> > extra >> > >> fields for code objects. >> > > Quick idea before I go to bed: >> > > >> > > You could adopt a similar API to OpenSSL's >> CRYPTO_get_ex_new_index() >> > > API, >> > > >> > https://www.openssl.org/docs/manmaster/crypto/CRYPTO_get_ >> ex_new_index.html >> > > >> > > >> > > static int code_index = 0; >> > > >> > > int PyCodeObject_NewIndex() { >> > > return code_index++; >> > > } >> > > >> > > A library like Pyjion has to acquire an index first. In further >> > calls it >> > > uses the index as offset into the new co_extra field. Libraries >> > don't >> > > have to hard-code their offset and two libraries will never >> > conflict. >> > > PyCode_New() can pre-populate co_extra with a PyTuple of size >> > > code_index. This avoids most resizes if you load Pyjion early. For >> > > code_index == 0 leaf the field NULL. >> > >> > Sounds like a very good idea! >> > >> > >> > The problem with this is the pre-population. If you don't get your >> > index assigned before the very first code object is allocated then you >> > still have to manage the size of the tuple in co_extra. So what this >> > would do is avoid the iteration but not the allocation overhead. >> > >> > If we open up the can of worms in terms of custom functions for this >> > (which I was trying to avoid), then you end up with Py_ssize_t >> > _PyCode_ExtraIndex(), PyObject * >> > _PyCode_GetExtra(PyCodeObject *code, Py_ssize_t index), and int >> > _PyCode_SetExtra(PyCodeObject *code, Py_ssize_t index, PyObject *data) >> > which does all the right things for creating or resizing the tuple as >> > necessary and which I think matches mostly what Nick had proposed >> > earlier. But the pseudo-code for _PyCode_GetExtra() would be:: >> > >> > if co_extra is None: >> > co_extra = (None,) * _next_extra_index; >> > return None >> > elif len(co_extra) < index - 1: >> > ... pad out tuple >> > return None >> > else: >> > return co_extra[index] >> > >> > Is that going to save us enough to want to have a custom API for this? >> >> But without that new API (basically what Christian proposed) you'd need >> to iterate over the list in order to find the object that belongs to >> Pyjion. > > > Yes. > > >> If we manage to implement my opcode caching idea, we'll have at >> least two known users of co_extra. Without a way to claim a particular >> index in co_extra you will have some overhead to locate your objects. >> > > Two things. One, I would want any new API to start with an underscore so > people know we can and will change its semantics as necessary. Two, Guido > would have to re-accept the PEP as this is a shift in the use of the field > if this is how people want to go. > > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > https://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: https://mail.python.org/mailman/options/python-dev/ > guido%40python.org > >
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