GeezerVison is showing github.com — Convert static types to heap types: use PyType_FromSpec() · Issue #84258 · python/cpython
Convert static types to heap types: use PyType_FromSpec() #84258Description
| BPO |
40077 |
| Nosy |
@pitrou, @vstinner, @phsilva, @encukou, @skrah, @ericsnowcurrently, @serhiy-storchaka, @corona10, @pablogsal, @miss-islington, @shihai1991, @erlend-aasland, @h-vetinari, @nw0, @kumaraditya303, @CharlieZhao95 |
| PRs |
bpo-40077: Convert _jsonmodule to use PyType_FromSpec. #19177bpo-40077: Convert _abc module to use PyType_FromSpec() #19202[WIP] bpo-40077: Convert _bz2 extension module to use PyType_FromSpec() #19341bpo-40077: Fix potential refleaks of _json #19344bpo-40077: Remove redundant cast in _json extension module #19438bpo-40077: Convert _bz2 module to use PyType_FromSpec #20960bpo-40077: Convert _csv module to use PyType_FromSpec #20974bpo-40077: Convert _operaator to use PyType_FromSpec #21953bpo-40077: Convert _operator to use PyType_FromSpec #21954bpo-40077: Convert mmap to use heap types #23108bpo-40077: Convert arraymodule to use heap types and establish module state #23124bpo-40077: Convert _queuemodule to use heap types #23136bpo-40077: Convert _elementtree types to heap types #23428bpo-42327: Add PyModule_Add() (smaller). #23443bpo-40077: Fix typo in simplequeue_get_state_by_type() #23975bpo-40077: Convert itertools types to heap types #24065bpo-40077: Add traverse/clear/free to arraymodule #24066bpo-40077: Convert zoneinfo type to heap type #24481bpo-40077: Convert _pickle module to use heap types. #30884 |
| Files |
bench_isinstance_check.pybench_subclass_check.pybench_isinstance_check.py |
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GitHub fields:
assignee = None
closed_at = None
created_at = <Date 2020-03-26.16:04:44.633>
labels = ['extension-modules', 'type-feature', '3.10']
title = 'Convert static types to heap types: use PyType_FromSpec()'
updated_at = <Date 2022-02-02.05:50:10.693>
user = 'https://github.com/corona10' bugs.python.org fields:
activity = <Date 2022-02-02.05:50:10.693>
actor = 'kumaraditya'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Extension Modules']
creation = <Date 2020-03-26.16:04:44.633>
creator = 'corona10'
dependencies = []
files = ['49007', '49008', '49009']
hgrepos = []
issue_num = 40077
keywords = ['patch']
message_count = 47.0
messages = ['365087', '365088', '365117', '365125', '365142', '365145', '365149', '365154', '365205', '365220', '365241', '365242', '365255', '365257', '365317', '365558', '365773', '366024', '366061', '368669', '371120', '371813', '371890', '372073', '372074', '372076', '372326', '375943', '380109', '380267', '380516', '380517', '380518', '383848', '383908', '384228', '384236', '384271', '384272', '384293', '410810', '411630', '411903', '411904', '411907', '411964', '412338']
nosy_count = 16.0
nosy_names = ['pitrou', 'vstinner', 'phsilva', 'petr.viktorin', 'skrah', 'eric.snow', 'serhiy.storchaka', 'corona10', 'pablogsal', 'miss-islington', 'shihai1991', 'erlendaasland', 'h-vetinari', 'nw0', 'kumaraditya', 'CharlieZhao']
pr_nums = ['19177', '19202', '19341', '19344', '19438', '20960', '20974', '21953', '21954', '23108', '23124', '23136', '23428', '23443', '23975', '24065', '24066', '24481', '30884']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue40077'
versions = ['Python 3.10'] Activitycorona10 commented on Mar 26, 2020 Some of modules is not using PyType_FromSpec.
We need to convert them.
This changes can bring
- allow to destroy types at exit!
- allow subinterpreters to have their own "isolated" typ
vstinner commented on Mar 26, 2020
We need to convert them.
Let me elaborate. Static types have multiple issues:
- Their lifetime is not well defined.
- It is not obvious when they are ready to be used.
- They are not destroyed at exit.
- They are incompatible with subinterpreters: each interpreter should have its own copy of a type, rather than static types are shared by all interpreters which cause problems with reference counting (require GIL or atomic operation).
- They are causing issues with stable ABI (limited C API): PEP-384.
pablogsal commented on Mar 26, 2020 Wouldn't having less static types slow down startup time? vstinner commented on Mar 27, 2020 Pablo:
Wouldn't having less static types slow down startup time?
That's possible, even if I only expect a minor or non significant overhead.
But before starting talking about performances, we should focus on the correctness. Static types are causing issues with subinterpreters and the Python finalization. vstinner commented on Mar 27, 2020 skrah commented on Mar 27, 2020 vstinner commented on Mar 27, 2020 In the _json module, PyModule_GetState() (called by get_json_state()) is only used by the garbage collector (traverse function) and to unload the module (clear and free functions). It's not used in "hot code" (let me consider that the GC is not part of the usual "hot code" :-)).
But maybe we should measure the overhead of future changes if PyModule_GetState() starts to be used in "hot code" by running a few microbenchmarks.
--
Stefan Krah:
Yes, and not only startup time:
https://bugs.python.org/issue15722
Aha, that's interesting. I didn't know that it could have an impact on runtime performance as well.
_decimal_pep3121-384_v1.patch attached to bpo-15722 seems to use:
#define _decimal_state_global ((_decimal_state *)PyModule_GetState(PyState_FindModule(&_decimal_module))) whereas the commit 33f15a1 only uses:
static inline _jsonmodulestate*
get_json_state(PyObject *module)
{
void *state = PyModule_GetState(module);
assert(state != NULL);
return (_jsonmodulestate *)state;
}Maybe PyState_FindModule() adds a little overhead, even if this function is simple: in short, it gets the i-th item of a list (from PyInterpreterState.modules_by_index).
PyModule_GetState() function is really simple: it only reads PyModuleObject.md_state attribute.
Or maybe _decimal_state_global was used in "hot code".
If PyState_FindModule() or PyModule_GetState() is the source of the overhead, maybe we could try to optimise these functions, or pass directly the module state to inner functions.
--
PyState_FindModule() doesn't work for a module using PyModuleDef_Init(). The PEP-573 is going to give access to the module state in functions which didn't access to it previsouly.
The commit 33f15a1 removed a few assertions checking that "self" has the expected type. It wasn't possible to get the module state to get the types, because PEP-573 is not implemented yet and PyState_FindModule() doesn't work in _json (which uses PyModuleDef_Init()). I decided that it's ok to remove these assertions: it should not be possible to call these functions with another type in practice.
--
In his PR 19177, Dong-hee started by replacing direct access to PyTypeObject fields, like replacing:
with:
freefunc free_func = PyType_GetSlot(tp, Py_tp_free);
free_func(self);
I asked him to revert these changes.
I'm interested to experiment a few C extension modules of the stdlib using the limited C API (PEP-384, stable ABI), but I don't think that it should done while converting modules to PyType_FromSpec().
We should separate the two changes. And I would prefer to first see the overhead of PyType_FromSpec(), and discuss the advantages and drawbacks. skrah commented on Mar 27, 2020
Or maybe _decimal_state_global was used in "hot code".
Yes, _decimal has problems here that most modules don't have.
Modules like atexit are obviously fine. :)
I just posted it as an example why one should be a bit cautious.
The PEP-573 is going to give access to the module state in functions which didn't access to it previously.
That could help, we'll see. corona10 commented on Mar 28, 2020
And I would prefer to first see the overhead of PyType_FromSpec(), and discuss the advantages and drawbacks.
Should we stop the work until the overhead is measured? vstinner commented on Mar 28, 2020
Should we stop the work until the overhead is measured?
Can you try to measure the _abc._abc_instancecheck() and _abc._abc_subclasscheck() functions performance before/after your change? Functions like register() are rarely call, so I don't care much of their performance (I expect a small overhead or no overhead). corona10 commented on Mar 29, 2020 It shown 1% slower for performance.
+--------------------------+-----------------+----------------------------+
| Benchmark | master-subclass | bpo-40077-subclass |
+==========================+=================+============================+
| bench _abc_subclasscheck | 295 ns | 300 ns: 1.01x slower (+1%) |
+--------------------------+-----------------+----------------------------+
+--------------------------+-------------------+----------------------------+
| Benchmark | master-isinstance | bpo-40077-isinstance |
+==========================+===================+============================+
| bench _abc_instancecheck | 229 ns | 232 ns: 1.01x slower (+1%) |
+--------------------------+-------------------+----------------------------+ vstinner commented on Jan 17, 2022 See also bpo-46417 "[subinterpreters] Clear static types in Py_Finalize()". vstinner commented on Jan 25, 2022 vstinner commented on Jan 27, 2022 I used the following shell command to search remaining static types:
---
grep -E 'static PyTypeObject [a-zA-Z_0-9]+ *(;|= *{|) *$' $(find -name "*.c")
---
I found 86 static types in 17 files:
vstinner commented on Jan 27, 2022 vstinner commented on Jan 27, 2022
And I found 135 more static types with this command
Of these 135 static types, most are cleared since bpo-46417 was implemented:
- 103 types are cleared by _PyTypes_FiniTypes()
- 15 types are cleared by _PyIO_Fini()
- the remaining 17 types are not cleared at Python exit: types of _ctypes, _curses and _multiprocessing extensions
vstinner commented on Jan 28, 2022 I marked bpo-23769 "valgrind reports leaks for test_zipimport" as duplicate of this issue. At exit, Python doesn't clear the static types of the _collections, itertools and _struct extensions:
- itertools.accumulate
- itertools.combinations
- itertools.combinations_with_replacement
- itertools.cycle
- itertools.dropwhile
- itertools.takewhile
- itertools.islice
- itertools.starmap
- itertools.chain
- itertools.compress
- itertools.filterfalse
- itertools.count
- itertools.zip_longest
- itertools.pairwise
- itertools.permutations
- itertools.product
- itertools.repeat
- itertools.groupby
- itertools._grouper
- itertools._tee
- itertools._tee_dataobject
- collections.deque
- _collections._deque_iterator
- _collections._deque_reverse_iterator
- _collections._tuplegetter
- _struct.Struct
- _struct.unpack_iterator
See: https://bugs.python.org/issue23769#msg411963 kumaraditya303 commented on Feb 2, 2022 On Windows PC/winreg.c has PyHKEY_Type static type which isn't cleared at exit too. kumaraditya303 commented on Jun 27, 2022 erlend-aasland commented on Jun 27, 2022
PEP 687 was accepted
Note that this does not imply that all types shall be converted to heap types. This is also mentioned in the PEP; please read it carefully. kumaraditya303 commented on Jun 28, 2022
Note that this does not imply that all types shall be converted to heap types. This is also mentioned in the PEP; please read it carefully.
We are on the same page, every module needs to considered individually and I am against converting any built-in modules or types unless it's necessary. kumaraditya303 commented on May 17, 2023
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