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GeezerVison is showing github.com — gh-112075: Add try-incref functions from nogil branch for use in dict thread safety by DinoV · Pull Request #114512 · python/cpython

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

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Merged

DinoV merged 3 commits into python:main from DinoV:nogil_tryincref

Jan 25, 2024

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

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39c251e

Bring in a subset of biased reference counting:

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136 changes: 136 additions & 0 deletions 136 Include/internal/pycore_object.h

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -376,6 +376,142 @@ static inline void _PyObject_GC_UNTRACK(
		_PyObject_GC_UNTRACK(__FILE__, __LINE__, _PyObject_CAST(op))
		#endif

		#ifdef Py_GIL_DISABLED

		/* Tries to increment an object's reference count
		*
		* This is a specialized version of _Py_TryIncref that only succeeds if the
		* object is immortal or local to this thread. It does not handle the case
		* where the reference count modification requires an atomic operation. This
		* allows call sites to specialize for the immortal/local case.
		*/
		static inline int
		_Py_TryIncrefFast(PyObject *op) {
		uint32_t local = _Py_atomic_load_uint32_relaxed(&op->ob_ref_local);
		local += 1;
		if (local == 0) {
		// immortal
		return 1;
		}
		if (_Py_IsOwnedByCurrentThread(op)) {
		_Py_INCREF_STAT_INC();
		_Py_atomic_store_uint32_relaxed(&op->ob_ref_local, local);
Comment thread DinoV marked this conversation as resolved. Resolved Uh oh! There was an error while loading. Please reload this page.
		#ifdef Py_REF_DEBUG
		_Py_IncRefTotal(_PyInterpreterState_GET());
		#endif
		return 1;
		}
		return 0;
		}

		static inline int
		_Py_TryIncRefShared(PyObject *op)
		{
		Py_ssize_t shared = _Py_atomic_load_ssize_relaxed(&op->ob_ref_shared);
		for (;;) {
		// If the shared refcount is zero and the object is either merged
		// or may not have weak references, then we cannot incref it.
		if (shared == 0 \|\| shared == _Py_REF_MERGED) {
		return 0;
		}

		if (_Py_atomic_compare_exchange_ssize(
		&op->ob_ref_shared,
		&shared,
		shared + (1 << _Py_REF_SHARED_SHIFT))) {
		#ifdef Py_REF_DEBUG
Comment thread DinoV marked this conversation as resolved. Resolved Uh oh! There was an error while loading. Please reload this page.
		_Py_IncRefTotal(_PyInterpreterState_GET());
		#endif
		_Py_INCREF_STAT_INC();
		return 1;
		}
		}
		}

		/* Tries to incref the object op and ensures that src still points to it. /
		static inline int
		_Py_TryIncref(PyObject *src, PyObject op)
		{
		if (_Py_TryIncrefFast(op)) {
		return 1;
		}
		if (!_Py_TryIncRefShared(op)) {
		return 0;
		}
		if (op != _Py_atomic_load_ptr(src)) {
		Py_DECREF(op);
		return 0;
		}
		return 1;
		}

		/* Loads and increfs an object from ptr, which may contain a NULL value.
		Safe with concurrent (atomic) updates to ptr.
		NOTE: The writer must set maybe-weakref on the stored object! */
		static inline PyObject *
		_Py_XGetRef(PyObject **ptr)
		{
		for (;;) {
		PyObject *value = _Py_atomic_load_ptr(ptr);
		if (value == NULL) {
		return value;
		}
		if (_Py_TryIncref(ptr, value)) {
		return value;
		}
		}
		}

		/* Attempts to loads and increfs an object from ptr. Returns NULL
		on failure, which may be due to a NULL value or a concurrent update. */
		static inline PyObject *
		_Py_TryXGetRef(PyObject **ptr)
		{
		PyObject *value = _Py_atomic_load_ptr(ptr);
		if (value == NULL) {
		return value;
		}
		if (_Py_TryIncref(ptr, value)) {
		return value;
		}
		return NULL;
		}

		/* Like Py_NewRef but also optimistically sets _Py_REF_MAYBE_WEAKREF
		on objects owned by a different thread. */
		static inline PyObject *
		_Py_NewRefWithLock(PyObject *op)
		{
		if (_Py_TryIncrefFast(op)) {
		return op;
		}
		_Py_INCREF_STAT_INC();
		for (;;) {
		Py_ssize_t shared = _Py_atomic_load_ssize_relaxed(&op->ob_ref_shared);
		Py_ssize_t new_shared = shared + (1 << _Py_REF_SHARED_SHIFT);
		if ((shared & _Py_REF_SHARED_FLAG_MASK) == 0) {
		new_shared \|= _Py_REF_MAYBE_WEAKREF;
		}
		if (_Py_atomic_compare_exchange_ssize(
		&op->ob_ref_shared,
		&shared,
		new_shared)) {
		return op;
		}
		}
		}

		static inline PyObject *
		_Py_XNewRefWithLock(PyObject *obj)
		{
		if (obj == NULL) {
		return NULL;
		}
		return _Py_NewRefWithLock(obj);
		}

		#endif

		#ifdef Py_REF_DEBUG
		extern void _PyInterpreterState_FinalizeRefTotal(PyInterpreterState *);
		extern void _Py_FinalizeRefTotal(_PyRuntimeState *);
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