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Draft: gh-123471: Make concurrent iteration over itertools.pairwise safe under free-threading #125417

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Draft: gh-123471: Make concurrent iteration over itertools.pairwise safe under free-threading #125417

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d7cbe16
Make pairwise_next safe for free-threading
eendebakpt Oct 13, 2024
c7ffc4f
refactor
eendebakpt Oct 14, 2024
fdc7b01
📜🤖 Added by blurb_it.
blurb-it[bot] Oct 14, 2024
e111e10
Merge branch 'main' into pairwise_v2
eendebakpt Oct 14, 2024
d6c48fc
Merge branch 'main' into pairwise_v2
eendebakpt Jan 28, 2025
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Make pairwise_next safe for free-threading
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@eendebakpt
eendebakpt committed Oct 13, 2024
commit d7cbe1695b607b8a5bd06dacb46af9268033252e
27 changes: 17 additions & 10 deletions Modules/itertoolsmodule.c
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Original file line number Diff line number Diff line change
Expand Up @@ -327,37 +327,43 @@ pairwise_traverse(pairwiseobject *po, visitproc visit, void *arg)
static PyObject *
pairwise_next(pairwiseobject *po)
{
PyObject *it = po->it;
PyObject *old = po->old;
PyObject *new, *result;

PyObject *it = Py_XNewRef(po->it);
if (it == NULL) {
return NULL;
}

PyObject *old = Py_XNewRef(po->old);
PyObject *new, *result;

if (old == NULL) {
old = (*Py_TYPE(it)->tp_iternext)(it);
Py_XSETREF(po->old, old);
if (old == NULL) {
Py_CLEAR(po->it);
Py_DECREF(it);
return NULL;
}
it = po->it;
if (it == NULL) {
Py_XSETREF(po->old, Py_NewRef(old));
if (po->it == NULL) {
// for re-entrant calls to pairwise next. the actual behavior is not important and this does not avoid any bugs (or does it?)
// the reason for having it is to make the behaviour equal to the python implementation behavior
Py_CLEAR(po->old);
Py_DECREF(old);
Py_DECREF(it);
return NULL;
}
}
Py_INCREF(old);

new = (*Py_TYPE(it)->tp_iternext)(it);
if (new == NULL) {
Py_CLEAR(po->it);
Py_CLEAR(po->old);
Py_DECREF(it);
Py_DECREF(old);
return NULL;
}

result = po->result;
if (Py_REFCNT(result) == 1) {
if (_PyObject_IsUniquelyReferenced(result)) {
Py_INCREF(result);
PyObject *last_old = PyTuple_GET_ITEM(result, 0);
PyObject *last_new = PyTuple_GET_ITEM(result, 1);
Expand All @@ -380,7 +386,8 @@ pairwise_next(pairwiseobject *po)
}

Py_XSETREF(po->old, new);
Py_DECREF(old);
Py_DECREF(old); // instead of the decref here we could borrow the reference above
Py_DECREF(it);
return result;
}

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