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Commitc44469c

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Add PyUnstable_TryIncref() and PyUnstable_EnableTryIncRef() (#159)
Co-authored-by: Victor Stinner <vstinner@python.org>
1 parente510a7b commitc44469c

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‎pythoncapi_compat.h‎

Lines changed: 75 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2231,6 +2231,81 @@ static inline int PyUnstable_Object_IsUniquelyReferenced(PyObject *obj)
22312231
}
22322232
#endif
22332233

2234+
// gh-128926 added PyUnstable_TryIncRef() and PyUnstable_EnableTryIncRef() to
2235+
// Python 3.14.0a5. Adapted from _Py_TryIncref() and _PyObject_SetMaybeWeakref().
2236+
#if PY_VERSION_HEX < 0x030E00A5
2237+
staticinlineintPyUnstable_TryIncRef(PyObject *op)
2238+
{
2239+
#ifndef Py_GIL_DISABLED
2240+
if (Py_REFCNT(op) >0) {
2241+
Py_INCREF(op);
2242+
return1;
2243+
}
2244+
return0;
2245+
#else
2246+
// _Py_TryIncrefFast()
2247+
uint32_t local =_Py_atomic_load_uint32_relaxed(&op->ob_ref_local);
2248+
local +=1;
2249+
if (local ==0) {
2250+
// immortal
2251+
return1;
2252+
}
2253+
if (_Py_IsOwnedByCurrentThread(op)) {
2254+
_Py_INCREF_STAT_INC();
2255+
_Py_atomic_store_uint32_relaxed(&op->ob_ref_local, local);
2256+
#ifdef Py_REF_DEBUG
2257+
_Py_INCREF_IncRefTotal();
2258+
#endif
2259+
return1;
2260+
}
2261+
2262+
// _Py_TryIncRefShared()
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Py_ssize_t shared =_Py_atomic_load_ssize_relaxed(&op->ob_ref_shared);
2264+
for (;;) {
2265+
// If the shared refcount is zero and the object is either merged
2266+
// or may not have weak references, then we cannot incref it.
2267+
if (shared ==0 || shared == _Py_REF_MERGED) {
2268+
return0;
2269+
}
2270+
2271+
if (_Py_atomic_compare_exchange_ssize(
2272+
&op->ob_ref_shared,
2273+
&shared,
2274+
shared + (1 << _Py_REF_SHARED_SHIFT))) {
2275+
#ifdef Py_REF_DEBUG
2276+
_Py_INCREF_IncRefTotal();
2277+
#endif
2278+
_Py_INCREF_STAT_INC();
2279+
return1;
2280+
}
2281+
}
2282+
#endif
2283+
}
2284+
2285+
staticinlinevoidPyUnstable_EnableTryIncRef(PyObject *op)
2286+
{
2287+
#ifdef Py_GIL_DISABLED
2288+
// _PyObject_SetMaybeWeakref()
2289+
if (_Py_IsImmortal(op)) {
2290+
return;
2291+
}
2292+
for (;;) {
2293+
Py_ssize_t shared =_Py_atomic_load_ssize_relaxed(&op->ob_ref_shared);
2294+
if ((shared & _Py_REF_SHARED_FLAG_MASK) !=0) {
2295+
// Nothing to do if it's in WEAKREFS, QUEUED, or MERGED states.
2296+
return;
2297+
}
2298+
if (_Py_atomic_compare_exchange_ssize(
2299+
&op->ob_ref_shared, &shared, shared | _Py_REF_MAYBE_WEAKREF)) {
2300+
return;
2301+
}
2302+
}
2303+
#else
2304+
(void)op;// unused argument
2305+
#endif
2306+
}
2307+
#endif
2308+
22342309

22352310
#if PY_VERSION_HEX < 0x030F0000
22362311
staticinline PyObject*

‎tests/test_pythoncapi_compat_cext.c‎

Lines changed: 48 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2448,6 +2448,46 @@ test_tuple(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
24482448
returntest_tuple_fromarray();
24492449
}
24502450

2451+
// Test adapted from CPython's _testcapi/object.c
2452+
staticintTryIncref_dealloc_called=0;
2453+
2454+
staticvoid
2455+
TryIncref_dealloc(PyObject*op)
2456+
{
2457+
// PyUnstable_TryIncRef should return 0 if object is being deallocated
2458+
assert(Py_REFCNT(op)==0);
2459+
assert(!PyUnstable_TryIncRef(op));
2460+
assert(Py_REFCNT(op)==0);
2461+
2462+
TryIncref_dealloc_called++;
2463+
Py_TYPE(op)->tp_free(op);
2464+
}
2465+
2466+
staticPyTypeObjectTryIncrefType;
2467+
2468+
staticPyObject*
2469+
test_try_incref(PyObject*Py_UNUSED(module),PyObject*Py_UNUSED(args))
2470+
{
2471+
TryIncref_dealloc_called=0;
2472+
2473+
PyObject*obj=PyObject_New(PyObject,&TryIncrefType);
2474+
if (obj==_Py_NULL) {
2475+
return_Py_NULL;
2476+
}
2477+
2478+
PyUnstable_EnableTryIncRef(obj);
2479+
2480+
Py_ssize_trefcount=Py_REFCNT(obj);
2481+
assert(PyUnstable_TryIncRef(obj));
2482+
assert(Py_REFCNT(obj)==refcount+1);
2483+
2484+
Py_DECREF(obj);
2485+
Py_DECREF(obj);
2486+
2487+
assert(TryIncref_dealloc_called==1);
2488+
Py_RETURN_NONE;
2489+
}
2490+
24512491

24522492
staticstructPyMethodDefmethods[]= {
24532493
{"test_object",test_object,METH_NOARGS,_Py_NULL},
@@ -2504,6 +2544,7 @@ static struct PyMethodDef methods[] = {
25042544
{"test_uniquely_referenced",test_uniquely_referenced,METH_NOARGS,_Py_NULL},
25052545
{"test_byteswriter",test_byteswriter,METH_NOARGS,_Py_NULL},
25062546
{"test_tuple",test_tuple,METH_NOARGS,_Py_NULL},
2547+
{"test_try_incref",test_try_incref,METH_NOARGS,_Py_NULL},
25072548
{_Py_NULL,_Py_NULL,0,_Py_NULL}
25082549
};
25092550

@@ -2532,6 +2573,13 @@ module_exec(PyObject *module)
25322573
return-1;
25332574
}
25342575
#endif
2576+
TryIncrefType.tp_name="TryIncrefType";
2577+
TryIncrefType.tp_basicsize=sizeof(PyObject);
2578+
TryIncrefType.tp_dealloc=TryIncref_dealloc;
2579+
TryIncrefType.tp_free=PyObject_Del;
2580+
if (PyType_Ready(&TryIncrefType)<0) {
2581+
return-1;
2582+
}
25352583
return0;
25362584
}
25372585

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