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Cowns: Fix Cown switch to be owned by GC #67

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Merged
xFrednet merged 2 commits into from
Feb 17, 2026
Merged

Cowns: Fix Cown switch to be owned by GC #67

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5b25e0c
fixup! Cowns: Add option to acquire a cown for the GC
kulisak12 Feb 3, 2026
f000cfc
fixup! Cowns: Allow switching owner to IP and back to GC
kulisak12 Feb 17, 2026
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12 changes: 7 additions & 5 deletions Objects/cownobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -618,7 +618,7 @@ int _PyCown_AcquireGC(_PyCownObject *self, Py_region_t *region) {

// The cown was snatched up by something else. This is fine for
// the GC
if (res != COWN_ACQUIRE_FAIL) {
if (res == COWN_ACQUIRE_FAIL) {
return 0;
}
assert(res == COWN_ACQUIRE_SUCCESS);
Expand All @@ -633,7 +633,7 @@ int _PyCown_SwitchFromGcToIp(_PyCownObject *self) {

_PyCown_ipid_t ipid = _PyCown_ThisInterpreterId();
_PyCown_ipid_t gcid = GC_IPID;
if (_Py_atomic_compare_exchange_uint64(&self->owning_ip, &gcid, ipid)) {
if (!_Py_atomic_compare_exchange_uint64(&self->owning_ip, &gcid, ipid)) {
return -1;
}

Expand All @@ -653,12 +653,12 @@ int _PyCown_SwitchFromIpToGc(_PyCownObject *self, Py_region_t *contained_region)
BAIL_UNLESS_OWNED_BY(self, ipid, -1);

PyObject *value = self->value;
Py_region_t value_region = _PyRegion_Get(value);
*contained_region = value_region;

// Cowns holding cowns or immutable objects can be released without any
// restrictions
Py_region_t value_region = _PyRegion_Get(value);
if (value_region == _Py_COWN_REGION || value_region == _Py_IMMUTABLE_REGION) {
*contained_region = value_region;
return cown_release_unchecked(self, ipid);
}

Expand All @@ -675,10 +675,12 @@ int _PyCown_SwitchFromIpToGc(_PyCownObject *self, Py_region_t *contained_region)

// A closed region is safe to release
if (_PyRegion_IsOpen(_PyRegion_Get(self->value))) {
*contained_region = NULL_REGION;
return 1;
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@xFrednet xFrednet Feb 17, 2026

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Suggested change
return 1;
*contained_region = NULL_REGION;
return 1;

}

if (_Py_atomic_compare_exchange_uint64(&self->owning_ip, &ipid, GC_IPID)) {
if (!_Py_atomic_compare_exchange_uint64(&self->owning_ip, &ipid, GC_IPID)) {
*contained_region = NULL_REGION;
return -1;
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@xFrednet xFrednet Feb 17, 2026

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Suggested change
return -1;
*contained_region = NULL_REGION;
return -1;

}
return 0;
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