Add API to allow extensions to set callback function on creation and destruction of PyCodeObject

[mpage]

BPO	46898
Nosy	@carljm, @DinoV, @itamaro, @mpage

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2022-03-01.22:20:58.520>
labels = ['expert-C-API', 'type-feature', '3.11']
title = 'Add API to allow extensions to set callback function on creation and destruction of PyCodeObject'
updated_at = <Date 2022-03-01.22:20:58.520>
user = 'https://github.com/mpage'

bugs.python.org fields:

activity = <Date 2022-03-01.22:20:58.520>
actor = 'mpage'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['C API']
creation = <Date 2022-03-01.22:20:58.520>
creator = 'mpage'
dependencies = []
files = []
hgrepos = []
issue_num = 46898
keywords = []
message_count = 1.0
messages = ['414309']
nosy_count = 4.0
nosy_names = ['carljm', 'dino.viehland', 'itamaro', 'mpage']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue46898'
versions = ['Python 3.11']

Linked PRs

• gh-91054: Add code object watchers API #99859
• gh-91054: Revert "gh-91054: Add code object watchers API" #99976
• GH-91054: Reset static events counts in code watchers tests #99978
• gh-91054: make code watcher tests resilient to other watchers #107821
• [3.12] gh-91054: make code watcher tests resilient to other watchers (GH-107821) #107835

[mpage]

CPython extensions providing optimized execution of Python bytecode (e.g. the Cinder JIT) may need to hook into the lifecycle of code objects to determine what to optimize or to free resources allocated for code objects that no longer exist. We propose adding an API to allow extensions to set callbacks that will be invoked whenever code objects are created or destroyed.

Proposed API:

typedef enum {
 PYCODE_LCEVT_CREATED,
 PYCODE_LCEVT_DESTROYED
} PyCode_LifecycleEvent;

// A callback to be called when a code object is created or about to be destroyed.
typedef void(*PyCode_LifecycleCallback)(
 PyCode_LifecycleEvent event,
 PyCodeObject* code);

void PyCode_SetLifecycleCallback(PyCode_LifecycleCallback callback);
PyCode_LifecycleCallback PyCode_GetLifecycleCallback();

[gvanrossum]

In which header file would you put that? Maybe this is simple enough that you should just submit a PR?

[itamaro]

In which header file would you put that?

would Include/cpython/code.h make sense for this API?

Maybe this is simple enough that you should just submit a PR?

hopefully yes, we intend to do that for 3.12.
does the proposed API look reasonable?

[gvanrossum]

The API looks reasonable -- I'd spell LifeCycle with two capital letters (though Wikipedia seems divided on this), and I'd start the enum values with PY_CODE, similar to _PyCodeLocationInfoKind in the same file. The implementation would seem straightforward, and code objects aren't created or destroyed at a monstrous rate (it might be worth seeing if this slows down unmarshalling noticeably, but I doubt it). The callback should probably be stored in the per-interpreter state.