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gh-112087: Use QSBR technique for list_new/clear for free-thread build #115875

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Merged
merged 10 commits into from
Mar 1, 2024
Merged

gh-112087: Use QSBR technique for list_new/clear for free-thread build #115875

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556c016
gh-112087: Use QSBR technique for list_new/clear for free-thread
corona10 Feb 24, 2024
67a7f32
Replace list_preallocate_exact to list_ensure_capacity
corona10 Feb 24, 2024
6ad0ab4
fix
corona10 Feb 24, 2024
6264094
Update test
corona10 Feb 24, 2024
e514c65
Update list_item
corona10 Feb 24, 2024
df90d37
Revert memory optimization changes
corona10 Feb 28, 2024
e7f3683
Address code review
corona10 Feb 28, 2024
0eb3657
Merge remote-tracking branch 'upstream/main' into gh-115605-qsbr
corona10 Feb 28, 2024
41204cf
Revert list_prealloc
corona10 Mar 1, 2024
9f5d048
nit
corona10 Mar 1, 2024
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35 changes: 29 additions & 6 deletions Objects/listobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -502,7 +502,16 @@ list_item(PyObject *aa, Py_ssize_t i)
PyErr_SetObject(PyExc_IndexError, &_Py_STR(list_err));
return NULL;
}
return Py_NewRef(a->ob_item[i]);
PyObject *item;
Py_BEGIN_CRITICAL_SECTION(a);
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@colesbury colesbury Feb 28, 2024

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We will want the fast path to do this without locking soon.

#ifdef Py_GIL_DISABLED
if (!_Py_IsOwnedByCurrentThread((PyObject *)a) && !_PyObject_GC_IS_SHARED(a)) {
_PyObject_GC_SET_SHARED(a);
}
#endif
item = Py_NewRef(a->ob_item[i]);
Py_END_CRITICAL_SECTION();
return item;
}

static PyObject *
Expand Down Expand Up @@ -658,7 +667,7 @@ list_repeat(PyObject *aa, Py_ssize_t n)
}

static void
list_clear(PyListObject *a)
list_clear_impl(PyListObject *a, bool is_resize)
{
PyObject **items = a->ob_item;
if (items == NULL) {
Expand All @@ -674,17 +683,31 @@ list_clear(PyListObject *a)
while (--i >= 0) {
Py_XDECREF(items[i]);
}
// TODO: Use QSBR technique, if the list is shared between threads,
PyMem_Free(items);

#ifdef Py_GIL_DISABLED
bool use_qsbr = is_resize && _PyObject_GC_IS_SHARED(a);
#else
bool use_qsbr = false;
#endif
if (use_qsbr) {
_PyMem_FreeDelayed(items);
}
else {
PyMem_Free(items);
}
// Note that there is no guarantee that the list is actually empty
// at this point, because XDECREF may have populated it indirectly again!
}

static void
list_clear(PyListObject *a)
{
list_clear_impl(a, true);
}

static int
list_clear_slot(PyObject *self)
{
list_clear((PyListObject *)self);
list_clear_impl((PyListObject *)self, false);
return 0;
}

Expand Down