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gh-112075: Add try-incref functions from nogil branch for use in dict thread safety #114512

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merged 3 commits into from
Jan 25, 2024

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@DinoV DinoV commented Jan 24, 2024

The NoGIL branch has functions for attempting to do an incref on an object which may or may not be in flight. This just brings those functions over so that they will be usable from in the dict implementation to get items w/o holding a lock.

There's a handful of small simple modifications:

  1. Adding inline to the force inline functions to avoid a warning, and switching from _Py_ALWAYS_INLINE to Py_ALWAYS_INLINE as that's available
  2. Remove _Py_REF_LOCAL_SHIFT as it doesn't exist yet (and is currently 0 in the 3.12 nogil branch anyway)
  3. ob_ref_shared is currently Py_ssize_t and not uint32_t, so use that
  4. _PY_LIKELY doesn't exist, so drop it
  5. _Py_ThreadLocal becomes _Py_IsOwnedByCurrentThread
  6. Add '_PyInterpreterState_GET()' to _Py_IncRefTotal calls.

@DinoV DinoV force-pushed the nogil_tryincref branch 4 times, most recently from 9318df9 to 818fc5f Compare January 24, 2024 18:52
@DinoV DinoV requested a review from colesbury January 24, 2024 19:10
@DinoV DinoV marked this pull request as ready for review January 24, 2024 19:25
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/* Tries to incref the object op and ensures that *src still points to it. */
static inline int
_Py_TryAcquireObject(PyObject **src, PyObject *op)
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I don't love this name, but I don't know what it should be called.

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I don't really have a better name either :P

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Maybe just _Py_TryIncref()? Also maybe rename src to ptr for consistency with the other functions here.

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A few minor suggestions, but otherwise LGTM.

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/* Tries to incref the object op and ensures that *src still points to it. */
static inline int
_Py_TryAcquireObject(PyObject **src, PyObject *op)
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Maybe just _Py_TryIncref()? Also maybe rename src to ptr for consistency with the other functions here.

@DinoV DinoV merged commit 4850410 into python:main Jan 25, 2024
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aisk pushed a commit to aisk/cpython that referenced this pull request Feb 11, 2024
…n dict thread safety (python#114512)

* Bring in a subset of biased reference counting:
colesbury/nogil@b6b12a9a94e

The NoGIL branch has functions for attempting to do an incref on an object which may or may not be in flight. This just brings those functions over so that they will be usable from in the dict implementation to get items w/o holding a lock.

There's a handful of small simple modifications:

    Adding inline to the force inline functions to avoid a warning, and switching from _Py_ALWAYS_INLINE to Py_ALWAYS_INLINE as that's available
    Remove _Py_REF_LOCAL_SHIFT as it doesn't exist yet (and is currently 0 in the 3.12 nogil branch anyway)
    ob_ref_shared is currently Py_ssize_t and not uint32_t, so use that
    _PY_LIKELY doesn't exist, so drop it
    _Py_ThreadLocal becomes _Py_IsOwnedByCurrentThread
    Add '_PyInterpreterState_GET()' to _Py_IncRefTotal calls.


Co-Authored-By: Sam Gross <[email protected]>
Glyphack pushed a commit to Glyphack/cpython that referenced this pull request Sep 2, 2024
…n dict thread safety (python#114512)

* Bring in a subset of biased reference counting:
colesbury/nogil@b6b12a9a94e

The NoGIL branch has functions for attempting to do an incref on an object which may or may not be in flight. This just brings those functions over so that they will be usable from in the dict implementation to get items w/o holding a lock.

There's a handful of small simple modifications:

    Adding inline to the force inline functions to avoid a warning, and switching from _Py_ALWAYS_INLINE to Py_ALWAYS_INLINE as that's available
    Remove _Py_REF_LOCAL_SHIFT as it doesn't exist yet (and is currently 0 in the 3.12 nogil branch anyway)
    ob_ref_shared is currently Py_ssize_t and not uint32_t, so use that
    _PY_LIKELY doesn't exist, so drop it
    _Py_ThreadLocal becomes _Py_IsOwnedByCurrentThread
    Add '_PyInterpreterState_GET()' to _Py_IncRefTotal calls.


Co-Authored-By: Sam Gross <[email protected]>
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