multi-core-python Up-to-date TODO list for per-interpreter GIL.

I'm moving the TODO, etc. to https://github.com/ericsnowcurrently/multi-core-python/wiki/0-The-Plan

Here's a rough TODO list, sort of in order (a lot can be done in parallel).

Note that most of these items fall out of Tools/c-analyzer/cpython/globals-to-fix.tsv. (Run ./python Tools/c-analyzer/table-file.py Tools/c-analyzer/cpython/globals-to-fix.tsv to get counts.)

(https://github.com/python/cpython/issues/84692)

Primary Tasks

[x] analysis (summary)
proposal: "A Per-Interpreter GIL"
- [x] initial python-dev discussion
- [x] clarify next steps with the steering council
- [x] write the proposal (PEP 684)
- [ ] accepted
tooling (to identify global variables)
- [x] analyze requirements & make design
- [x] implement the tool (Tools/c-analyzer)
- [ ] re-enable CI check to prevent addition of more globals (may need fixes)
resolve main blockers
- [ ] objects exposed in public C-API (solve with immortal objects)
- [ ] shared vs. per-interpreter allocators (solve with mimalloc)
- [ ] impact on extension maintainers (solve with docs, work with numpy)
implementation
- prerequisites
  - [x] simplify runtime init/fini code (PEP 432, PEP 587)
  - [x] introduce _PyRuntimeState
- consolidate globals (#81057)
  - [x] ... (move a bunch of stuff into _PyRuntimeState)
  - [x] ... (statically init a bunch of global objects)
  - [ ] (maybe?) move some state from PyInterpreterState to _PyRuntimeState
  - [ ] drop _Py_IDENTIFIER() in extensions (or modify it to use a statically initialized str?)
    - [ ] Modules/_asynciomodule.c
    - [ ] Modules/_ctypes/callbacks.c
    - [ ] Modules/_ctypes/callproc.c
    - [ ] Modules/_ctypes/_ctypes.c
    - [ ] Modules/_ctypes/stgdict.c
    - [ ] Modules/_cursesmodule.c
    - [ ] Modules/_datetimemodule.c
    - [ ] Modules/_elementtree.c
    - [ ] Modules/_json.c
    - [ ] Modules/ossaudiodev.c
    - [ ] Modules/_testcapimodule.c
    - [ ] Programs/_testembed.c
  - [x] statically init latin-1 chars
  - [ ] statically init currently cached str objects
  - [ ] deal with PyArg_Parser (#90928, #82322, faster-cpython#281)
  - [ ] pull remaining objects into _PyRuntimeState
  - [ ] pull remaining state into _PyRuntimeState
- prep for per-interpreter state
  - [ ] solve per-interpreter state for core/builtin static types (e.g. dynamic lookup for some attrs)
  - [ ] solve for extensions
  - [ ] make some vars atomic?
  - [ ] convert stdlib extensions to PEP 630 (see bpo-40077, PEP 687 & the SC discussion)
- add new C-API and implement runtime machinery
  - [ ] ...
- move state (incl. GIL) to PyInterpreterState
  - [ ] enforce restrictions on importing extensions...
  - [ ] finally: move some state/objects to PyInterpreterState
  - [ ] 💥 move the GIL to PyInterpreterState 💥

Solutions for Blockers

Immortal Objects:

[x] analysis, design, and initial discussion (bpo-40255)
[x] implement basic solution (gh-19474)
[x] run benchmarks (incl. with all objects immortalized at end of runtime init)
[ ] (maybe?) prepare a contingency plan for if we don't end up with immortal objects
[x] write a proposal (PEP 683)
[x] present at the language summit
[x] enumerate other strategies for getting back to performance neutral
[x] implement them
[ ] PEP accepted
[ ] merge implementation

mimalloc (thread-safe, performant allocator):

[x] get mimalloc working as CPython's allocator (Christian: ...)
[ ] add static analyzer support (ASAN, valgrind) (Daan)
[ ] resolve problem with leaking large blocks (Daan/Christian)
[ ] resolve PGO issues on Windows (Eric: contact MSVC team)
[ ] merge the implementation
[ ] sort out GIL guarantees for allocator API

Reduce Impact on Extension Maintainers:

[ ] add docs (i.e. copy PEP 630)
[ ] (probably) add some new C-API to solve pain points
[ ] work with numpy, specifically, to add support for multiple interpreters
[ ] work with cython

Secondary Tasks

[ ] finish "c-analyzer.py data count"
[ ] fix "c-analyzer.py data check" & add to CI
[ ] statically init other immutables
[ ] ...

Other Related Items

PEP 554 (stdlib module to expose multiple interpreters)
help numpy, cython, etc.
PEP: add Public C-API as replacement for _Py_IDENTIFIER() (@zooba's staticstr?)
"subinterpreters" project: https://github.com/orgs/python/projects/3/views/1

Feb 09 '22 23:02 ericsnowcurrently

FYI, here's a recent breakdown of the remaining globals:

core/builtins (651 total)
- 298 static types (incl. 130 exception types)
- 179 cached objects (e.g. str instances)
- 57 other objects
- 117 non-object (incl. 60 state)
extension modules (605 total)
- 78 static types
- 317 cached objects (e.g. str instances)
- 145 other objects
- 65 non-object (incl. 29 state)

(the detailed breakdown)

./python Tools/c-analyzer/table-file.py Tools/c-analyzer/cpython/globals-to-fix.tsv
 --------------------------------------------------
  (365)       global objects to fix in core code
         119      static types
         130      builtin exception types
           9      singletons
   (98)           cached - initialized once
          39          manually cached PyUnicodeObject
          54          _PyArg_Parser (holds tuple of strings)
           1          holds strings
           4          other
    (9)           other
           7          initialized once
           2          state
 --------------------------------------------------
   (94)       global non-objects to fix in core code
   (29)           initialized/set once
           1          pre-allocated buffer
          13          during init
          15          lazy
   (20)           unlikely to change after init (or main thread)
          11          through C-API
           4          REPL
           5          handling C argv
   (45)           state
          15          allocator
           2          pre-allocated memory
           2          local buffer
           2          linked list
          24          other
 --------------------------------------------------
  (169)       global objects to fix in builtin modules
          22      modules
          49      static types
    (5)           non-static types - initialized once
           3          structseq types
           2          exception types
   (81)           cached - initialized once
          29          manually cached PyUnicodeOjbect
          52          _PyArg_Parser
   (12)           other
           6          initialized once
           6          state
 --------------------------------------------------
   (23)       global non-objects to fix in builtin modules
           8      initialized once
          15      state
 --------------------------------------------------
  (540)       global objects to fix in extension modules
          65      modules
          78      static types
   (34)           non-static types - initialized once
           3          structseq types
           6          heap types
          25          exception types
  (317)           cached - initialized once
          18          _Py_IDENTIFIER (global)
         149          _Py_IDENTIFIER (local)
           1          _Py_static_string
          12          manually cached PyUnicodeOjbect
         124          _PyArg_Parser
          13          other - during module init
   (46)           other
          31          initialized once
          15          state
 --------------------------------------------------
   (65)       global non-objects to fix in extension modules
   (36)           initialized once
           2          pre-allocated buffer
          34          other
          29      state
 --------------------------------------------------
(total: 1256)

Feb 14 '22 19:02 ericsnowcurrently

statically init latin-1 chars is done https://bugs.python.org/issue46881

Mar 12 '22 10:03 kumaraditya303