diff --git a/Include/cpython/object.h b/Include/cpython/object.h
index 90cd7b54b34..e1024ddbdf6 100644
--- a/Include/cpython/object.h
+++ b/Include/cpython/object.h
@@ -270,6 +270,9 @@ typedef struct _heaptypeobject {
PyObject *ht_module;
char *_ht_tpname; // Storage for "tp_name"; see PyType_FromModuleAndSpec
struct _specialization_cache _spec_cache; // For use by the specializer.
+#ifdef Py_GIL_DISABLED
+ Py_ssize_t unique_id; // ID used for thread-local refcounting
+#endif
/* here are optional user slots, followed by the members. */
} PyHeapTypeObject;
diff --git a/Include/internal/pycore_gc.h b/Include/internal/pycore_gc.h
index b4bf36e82e3..5dd5b0c78d4 100644
--- a/Include/internal/pycore_gc.h
+++ b/Include/internal/pycore_gc.h
@@ -381,10 +381,6 @@ extern void _PyGC_ClearAllFreeLists(PyInterpreterState *interp);
extern void _Py_ScheduleGC(PyThreadState *tstate);
extern void _Py_RunGC(PyThreadState *tstate);
-#ifdef Py_GIL_DISABLED
-// gh-117783: Immortalize objects that use deferred reference counting
-extern void _PyGC_ImmortalizeDeferredObjects(PyInterpreterState *interp);
-#endif
#ifdef __cplusplus
}
diff --git a/Include/internal/pycore_interp.h b/Include/internal/pycore_interp.h
index 4a83862ac13..a1c1dd0c957 100644
--- a/Include/internal/pycore_interp.h
+++ b/Include/internal/pycore_interp.h
@@ -35,6 +35,7 @@ extern "C" {
#include "pycore_qsbr.h" // struct _qsbr_state
#include "pycore_tstate.h" // _PyThreadStateImpl
#include "pycore_tuple.h" // struct _Py_tuple_state
+#include "pycore_typeid.h" // struct _Py_type_id_pool
#include "pycore_typeobject.h" // struct types_state
#include "pycore_unicodeobject.h" // struct _Py_unicode_state
#include "pycore_warnings.h" // struct _warnings_runtime_state
@@ -220,6 +221,7 @@ struct _is {
#if defined(Py_GIL_DISABLED)
struct _mimalloc_interp_state mimalloc;
struct _brc_state brc; // biased reference counting state
+ struct _Py_type_id_pool type_ids;
PyMutex weakref_locks[NUM_WEAKREF_LIST_LOCKS];
#endif
diff --git a/Include/internal/pycore_object.h b/Include/internal/pycore_object.h
index 155810d00be..a5640b7bcb7 100644
--- a/Include/internal/pycore_object.h
+++ b/Include/internal/pycore_object.h
@@ -14,10 +14,19 @@ extern "C" {
#include "pycore_interp.h" // PyInterpreterState.gc
#include "pycore_pyatomic_ft_wrappers.h" // FT_ATOMIC_STORE_PTR_RELAXED
#include "pycore_pystate.h" // _PyInterpreterState_GET()
+#include "pycore_typeid.h" // _PyType_IncrefSlow
#define _Py_IMMORTAL_REFCNT_LOOSE ((_Py_IMMORTAL_REFCNT >> 1) + 1)
+// This value is added to `ob_ref_shared` for objects that use deferred
+// reference counting so that they are not immediately deallocated when the
+// non-deferred reference count drops to zero.
+//
+// The value is half the maximum shared refcount because the low two bits of
+// `ob_ref_shared` are used for flags.
+#define _Py_REF_DEFERRED (PY_SSIZE_T_MAX / 8)
+
// gh-121528, gh-118997: Similar to _Py_IsImmortal() but be more loose when
// comparing the reference count to stay compatible with C extensions built
// with the stable ABI 3.11 or older. Such extensions implement INCREF/DECREF
@@ -280,6 +289,67 @@ extern PyStatus _PyObject_InitState(PyInterpreterState *interp);
extern void _PyObject_FiniState(PyInterpreterState *interp);
extern bool _PyRefchain_IsTraced(PyInterpreterState *interp, PyObject *obj);
+#ifndef Py_GIL_DISABLED
+# define _Py_INCREF_TYPE Py_INCREF
+# define _Py_DECREF_TYPE Py_DECREF
+#else
+static inline void
+_Py_INCREF_TYPE(PyTypeObject *type)
+{
+ if (!_PyType_HasFeature(type, Py_TPFLAGS_HEAPTYPE)) {
+ assert(_Py_IsImmortal(type));
+ return;
+ }
+
+ _PyThreadStateImpl *tstate = (_PyThreadStateImpl *)_PyThreadState_GET();
+ PyHeapTypeObject *ht = (PyHeapTypeObject *)type;
+
+ // Unsigned comparison so that `unique_id=-1`, which indicates that
+ // per-thread refcounting has been disabled on this type, is handled by
+ // the "else".
+ if ((size_t)ht->unique_id < (size_t)tstate->types.size) {
+# ifdef Py_REF_DEBUG
+ _Py_INCREF_IncRefTotal();
+# endif
+ _Py_INCREF_STAT_INC();
+ tstate->types.refcounts[ht->unique_id]++;
+ }
+ else {
+ // The slow path resizes the thread-local refcount array if necessary.
+ // It handles the unique_id=-1 case to keep the inlinable function smaller.
+ _PyType_IncrefSlow(ht);
+ }
+}
+
+static inline void
+_Py_DECREF_TYPE(PyTypeObject *type)
+{
+ if (!_PyType_HasFeature(type, Py_TPFLAGS_HEAPTYPE)) {
+ assert(_Py_IsImmortal(type));
+ return;
+ }
+
+ _PyThreadStateImpl *tstate = (_PyThreadStateImpl *)_PyThreadState_GET();
+ PyHeapTypeObject *ht = (PyHeapTypeObject *)type;
+
+ // Unsigned comparison so that `unique_id=-1`, which indicates that
+ // per-thread refcounting has been disabled on this type, is handled by
+ // the "else".
+ if ((size_t)ht->unique_id < (size_t)tstate->types.size) {
+# ifdef Py_REF_DEBUG
+ _Py_DECREF_DecRefTotal();
+# endif
+ _Py_DECREF_STAT_INC();
+ tstate->types.refcounts[ht->unique_id]--;
+ }
+ else {
+ // Directly decref the type if the type id is not assigned or if
+ // per-thread refcounting has been disabled on this type.
+ Py_DECREF(type);
+ }
+}
+#endif
+
/* Inline functions trading binary compatibility for speed:
_PyObject_Init() is the fast version of PyObject_Init(), and
_PyObject_InitVar() is the fast version of PyObject_InitVar().
@@ -291,7 +361,7 @@ _PyObject_Init(PyObject *op, PyTypeObject *typeobj)
assert(op != NULL);
Py_SET_TYPE(op, typeobj);
assert(_PyType_HasFeature(typeobj, Py_TPFLAGS_HEAPTYPE) || _Py_IsImmortalLoose(typeobj));
- Py_INCREF(typeobj);
+ _Py_INCREF_TYPE(typeobj);
_Py_NewReference(op);
}
diff --git a/Include/internal/pycore_tstate.h b/Include/internal/pycore_tstate.h
index 18c972bd367..f681b644c9a 100644
--- a/Include/internal/pycore_tstate.h
+++ b/Include/internal/pycore_tstate.h
@@ -31,6 +31,16 @@ typedef struct _PyThreadStateImpl {
struct _mimalloc_thread_state mimalloc;
struct _Py_freelists freelists;
struct _brc_thread_state brc;
+ struct {
+ // The thread-local refcounts for heap type objects
+ Py_ssize_t *refcounts;
+
+ // Size of the refcounts array.
+ Py_ssize_t size;
+
+ // If set, don't use thread-local refcounts
+ int is_finalized;
+ } types;
#endif
#if defined(Py_REF_DEBUG) && defined(Py_GIL_DISABLED)
diff --git a/Include/internal/pycore_typeid.h b/Include/internal/pycore_typeid.h
new file mode 100644
index 00000000000..e64d1447f6b
--- /dev/null
+++ b/Include/internal/pycore_typeid.h
@@ -0,0 +1,75 @@
+#ifndef Py_INTERNAL_TYPEID_H
+#define Py_INTERNAL_TYPEID_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef Py_BUILD_CORE
+# error "this header requires Py_BUILD_CORE define"
+#endif
+
+#ifdef Py_GIL_DISABLED
+
+// This contains code for allocating unique ids to heap type objects
+// and re-using those ids when the type is deallocated.
+//
+// The type ids are used to implement per-thread reference counts of
+// heap type objects to avoid contention on the reference count fields
+// of heap type objects. Static type objects are immortal, so contention
+// is not an issue for those types.
+//
+// Type id of -1 is used to indicate a type doesn't use thread-local
+// refcounting. This value is used when a type object is finalized by the GC
+// and during interpreter shutdown to allow the type object to be
+// deallocated promptly when the object's refcount reaches zero.
+//
+// Each entry implicitly represents a type id based on it's offset in the
+// table. Non-allocated entries form a free-list via the 'next' pointer.
+// Allocated entries store the corresponding PyTypeObject.
+typedef union _Py_type_id_entry {
+ // Points to the next free type id, when part of the freelist
+ union _Py_type_id_entry *next;
+
+ // Stores the type object when the id is assigned
+ PyHeapTypeObject *type;
+} _Py_type_id_entry;
+
+struct _Py_type_id_pool {
+ PyMutex mutex;
+
+ // combined table of types with allocated type ids and unallocated
+ // type ids.
+ _Py_type_id_entry *table;
+
+ // Next entry to allocate inside 'table' or NULL
+ _Py_type_id_entry *freelist;
+
+ // size of 'table'
+ Py_ssize_t size;
+};
+
+// Assigns the next id from the pool of type ids.
+extern void _PyType_AssignId(PyHeapTypeObject *type);
+
+// Releases the allocated type id back to the pool.
+extern void _PyType_ReleaseId(PyHeapTypeObject *type);
+
+// Merges the thread-local reference counts into the corresponding types.
+extern void _PyType_MergeThreadLocalRefcounts(_PyThreadStateImpl *tstate);
+
+// Like _PyType_MergeThreadLocalRefcounts, but also frees the thread-local
+// array of refcounts.
+extern void _PyType_FinalizeThreadLocalRefcounts(_PyThreadStateImpl *tstate);
+
+// Frees the interpreter's pool of type ids.
+extern void _PyType_FinalizeIdPool(PyInterpreterState *interp);
+
+// Increfs the type, resizing the thread-local refcount array if necessary.
+PyAPI_FUNC(void) _PyType_IncrefSlow(PyHeapTypeObject *type);
+
+#endif /* Py_GIL_DISABLED */
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* !Py_INTERNAL_TYPEID_H */
diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
index 709355e293f..42b5a7c94e7 100644
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -1710,6 +1710,7 @@ class SizeofTest(unittest.TestCase):
fmt = 'P2nPI13Pl4Pn9Pn12PIPc'
s = vsize(fmt)
check(int, s)
+ typeid = 'n' if support.Py_GIL_DISABLED else ''
# class
s = vsize(fmt + # PyTypeObject
'4P' # PyAsyncMethods
@@ -1718,7 +1719,8 @@ class SizeofTest(unittest.TestCase):
'10P' # PySequenceMethods
'2P' # PyBufferProcs
'6P'
- '1PIP' # Specializer cache
+ '1PIP' # Specializer cache
+ + typeid # heap type id (free-threaded only)
)
class newstyleclass(object): pass
# Separate block for PyDictKeysObject with 8 keys and 5 entries
diff --git a/Makefile.pre.in b/Makefile.pre.in
index 5608e593ac9..66b3665e9c2 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -483,6 +483,7 @@ PYTHON_OBJS= \
Python/thread.o \
Python/traceback.o \
Python/tracemalloc.o \
+ Python/typeid.o \
Python/getopt.o \
Python/pystrcmp.o \
Python/pystrtod.o \
@@ -1257,6 +1258,7 @@ PYTHON_HEADERS= \
$(srcdir)/Include/internal/pycore_tracemalloc.h \
$(srcdir)/Include/internal/pycore_tstate.h \
$(srcdir)/Include/internal/pycore_tuple.h \
+ $(srcdir)/Include/internal/pycore_typeid.h \
$(srcdir)/Include/internal/pycore_typeobject.h \
$(srcdir)/Include/internal/pycore_typevarobject.h \
$(srcdir)/Include/internal/pycore_ucnhash.h \
diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2024-07-29-19-20-25.gh-issue-122417.NVgs0a.rst b/Misc/NEWS.d/next/Core_and_Builtins/2024-07-29-19-20-25.gh-issue-122417.NVgs0a.rst
new file mode 100644
index 00000000000..b050c9ce39c
--- /dev/null
+++ b/Misc/NEWS.d/next/Core_and_Builtins/2024-07-29-19-20-25.gh-issue-122417.NVgs0a.rst
@@ -0,0 +1,4 @@
+In the free-threaded build, the reference counts for heap type objects are now
+partially stored in a distributed manner in per-thread arrays. This reduces
+contention on the heap type's reference count fields when creating or
+destroying instances of the same type from multiple threads concurrently.
diff --git a/Objects/object.c b/Objects/object.c
index db9d3e46795..c6d46caa0bb 100644
--- a/Objects/object.c
+++ b/Objects/object.c
@@ -2477,15 +2477,7 @@ _PyObject_SetDeferredRefcount(PyObject *op)
assert(_Py_IsOwnedByCurrentThread(op));
assert(op->ob_ref_shared == 0);
_PyObject_SET_GC_BITS(op, _PyGC_BITS_DEFERRED);
- PyInterpreterState *interp = _PyInterpreterState_GET();
- if (_Py_atomic_load_int_relaxed(&interp->gc.immortalize) == 1) {
- // gh-117696: immortalize objects instead of using deferred reference
- // counting for now.
- _Py_SetImmortal(op);
- return;
- }
- op->ob_ref_local += 1;
- op->ob_ref_shared = _Py_REF_QUEUED;
+ op->ob_ref_shared = _Py_REF_SHARED(_Py_REF_DEFERRED, 0);
#endif
}
diff --git a/Objects/typeobject.c b/Objects/typeobject.c
index a2d82e65b6a..00f0dc9849b 100644
--- a/Objects/typeobject.c
+++ b/Objects/typeobject.c
@@ -2452,7 +2452,7 @@ subtype_dealloc(PyObject *self)
reference counting. Only decref if the base type is not already a heap
allocated type. Otherwise, basedealloc should have decref'd it already */
if (type_needs_decref) {
- Py_DECREF(type);
+ _Py_DECREF_TYPE(type);
}
/* Done */
@@ -2562,7 +2562,7 @@ subtype_dealloc(PyObject *self)
reference counting. Only decref if the base type is not already a heap
allocated type. Otherwise, basedealloc should have decref'd it already */
if (type_needs_decref) {
- Py_DECREF(type);
+ _Py_DECREF_TYPE(type);
}
endlabel:
@@ -3913,7 +3913,9 @@ type_new_alloc(type_new_ctx *ctx)
et->ht_module = NULL;
et->_ht_tpname = NULL;
- _PyObject_SetDeferredRefcount((PyObject *)et);
+#ifdef Py_GIL_DISABLED
+ _PyType_AssignId(et);
+#endif
return type;
}
@@ -4965,6 +4967,11 @@ _PyType_FromMetaclass_impl(
type->tp_weaklistoffset = weaklistoffset;
type->tp_dictoffset = dictoffset;
+#ifdef Py_GIL_DISABLED
+ // Assign a type id to enable thread-local refcounting
+ _PyType_AssignId(res);
+#endif
+
/* Ready the type (which includes inheritance).
*
* After this call we should generally only touch up what's
@@ -5914,6 +5921,9 @@ type_dealloc(PyObject *self)
}
Py_XDECREF(et->ht_module);
PyMem_Free(et->_ht_tpname);
+#ifdef Py_GIL_DISABLED
+ _PyType_ReleaseId(et);
+#endif
Py_TYPE(type)->tp_free((PyObject *)type);
}
diff --git a/PCbuild/_freeze_module.vcxproj b/PCbuild/_freeze_module.vcxproj
index e5e18de60ec..962d754e4a1 100644
--- a/PCbuild/_freeze_module.vcxproj
+++ b/PCbuild/_freeze_module.vcxproj
@@ -267,6 +267,7 @@
+
diff --git a/PCbuild/_freeze_module.vcxproj.filters b/PCbuild/_freeze_module.vcxproj.filters
index 9630f54ae4e..86146f73857 100644
--- a/PCbuild/_freeze_module.vcxproj.filters
+++ b/PCbuild/_freeze_module.vcxproj.filters
@@ -464,6 +464,9 @@
Source Files
+
+ Source Files
+
Source Files
diff --git a/PCbuild/pythoncore.vcxproj b/PCbuild/pythoncore.vcxproj
index 9e3af689f4a..7991eb93aa2 100644
--- a/PCbuild/pythoncore.vcxproj
+++ b/PCbuild/pythoncore.vcxproj
@@ -304,6 +304,7 @@
+
@@ -643,6 +644,7 @@
+
diff --git a/PCbuild/pythoncore.vcxproj.filters b/PCbuild/pythoncore.vcxproj.filters
index 31f7971bda8..075910915fb 100644
--- a/PCbuild/pythoncore.vcxproj.filters
+++ b/PCbuild/pythoncore.vcxproj.filters
@@ -831,6 +831,9 @@
Include\internal
+
+ Include\internal
+
Include\internal
@@ -1493,6 +1496,9 @@
Python
+
+ Python
+
Python
diff --git a/Python/gc_free_threading.c b/Python/gc_free_threading.c
index 53f04160c38..1e02db00649 100644
--- a/Python/gc_free_threading.c
+++ b/Python/gc_free_threading.c
@@ -15,6 +15,7 @@
#include "pycore_tstate.h" // _PyThreadStateImpl
#include "pycore_weakref.h" // _PyWeakref_ClearRef()
#include "pydtrace.h"
+#include "pycore_typeid.h" // _PyType_MergeThreadLocalRefcounts
#ifdef Py_GIL_DISABLED
@@ -164,7 +165,15 @@ disable_deferred_refcounting(PyObject *op)
{
if (_PyObject_HasDeferredRefcount(op)) {
op->ob_gc_bits &= ~_PyGC_BITS_DEFERRED;
- op->ob_ref_shared -= (1 << _Py_REF_SHARED_SHIFT);
+ op->ob_ref_shared -= _Py_REF_SHARED(_Py_REF_DEFERRED, 0);
+
+ if (PyType_Check(op)) {
+ // Disable thread-local refcounting for heap types
+ PyTypeObject *type = (PyTypeObject *)op;
+ if (PyType_HasFeature(type, Py_TPFLAGS_HEAPTYPE)) {
+ _PyType_ReleaseId((PyHeapTypeObject *)op);
+ }
+ }
}
}
@@ -328,16 +337,6 @@ merge_queued_objects(_PyThreadStateImpl *tstate, struct collection_state *state)
}
}
-static void
-merge_all_queued_objects(PyInterpreterState *interp, struct collection_state *state)
-{
- HEAD_LOCK(&_PyRuntime);
- for (PyThreadState *p = interp->threads.head; p != NULL; p = p->next) {
- merge_queued_objects((_PyThreadStateImpl *)p, state);
- }
- HEAD_UNLOCK(&_PyRuntime);
-}
-
static void
process_delayed_frees(PyInterpreterState *interp)
{
@@ -389,7 +388,9 @@ update_refs(const mi_heap_t *heap, const mi_heap_area_t *area,
}
Py_ssize_t refcount = Py_REFCNT(op);
- refcount -= _PyObject_HasDeferredRefcount(op);
+ if (_PyObject_HasDeferredRefcount(op)) {
+ refcount -= _Py_REF_DEFERRED;
+ }
_PyObject_ASSERT(op, refcount >= 0);
if (refcount > 0 && !_PyObject_HasDeferredRefcount(op)) {
@@ -754,10 +755,6 @@ _PyGC_Init(PyInterpreterState *interp)
{
GCState *gcstate = &interp->gc;
- // gh-117783: immortalize objects that would use deferred refcounting
- // once the first non-main thread is created (but not in subinterpreters).
- gcstate->immortalize = _Py_IsMainInterpreter(interp) ? 0 : -1;
-
gcstate->garbage = PyList_New(0);
if (gcstate->garbage == NULL) {
return _PyStatus_NO_MEMORY();
@@ -1105,8 +1102,18 @@ gc_collect_internal(PyInterpreterState *interp, struct collection_state *state,
state->gcstate->old[i-1].count = 0;
}
- // merge refcounts for all queued objects
- merge_all_queued_objects(interp, state);
+ HEAD_LOCK(&_PyRuntime);
+ for (PyThreadState *p = interp->threads.head; p != NULL; p = p->next) {
+ _PyThreadStateImpl *tstate = (_PyThreadStateImpl *)p;
+
+ // merge per-thread refcount for types into the type's actual refcount
+ _PyType_MergeThreadLocalRefcounts(tstate);
+
+ // merge refcounts for all queued objects
+ merge_queued_objects(tstate, state);
+ }
+ HEAD_UNLOCK(&_PyRuntime);
+
process_delayed_frees(interp);
// Find unreachable objects
@@ -1835,32 +1842,6 @@ custom_visitor_wrapper(const mi_heap_t *heap, const mi_heap_area_t *area,
return true;
}
-// gh-117783: Immortalize objects that use deferred reference counting to
-// temporarily work around scaling bottlenecks.
-static bool
-immortalize_visitor(const mi_heap_t *heap, const mi_heap_area_t *area,
- void *block, size_t block_size, void *args)
-{
- PyObject *op = op_from_block(block, args, false);
- if (op != NULL && _PyObject_HasDeferredRefcount(op)) {
- _Py_SetImmortal(op);
- op->ob_gc_bits &= ~_PyGC_BITS_DEFERRED;
- }
- return true;
-}
-
-void
-_PyGC_ImmortalizeDeferredObjects(PyInterpreterState *interp)
-{
- struct visitor_args args;
- _PyEval_StopTheWorld(interp);
- if (interp->gc.immortalize == 0) {
- gc_visit_heaps(interp, &immortalize_visitor, &args);
- interp->gc.immortalize = 1;
- }
- _PyEval_StartTheWorld(interp);
-}
-
void
PyUnstable_GC_VisitObjects(gcvisitobjects_t callback, void *arg)
{
diff --git a/Python/pystate.c b/Python/pystate.c
index 6fbd17f7eae..8f4818cee00 100644
--- a/Python/pystate.c
+++ b/Python/pystate.c
@@ -20,6 +20,7 @@
#include "pycore_runtime_init.h" // _PyRuntimeState_INIT
#include "pycore_sysmodule.h" // _PySys_Audit()
#include "pycore_obmalloc.h" // _PyMem_obmalloc_state_on_heap()
+#include "pycore_typeid.h" // _PyType_FinalizeIdPool
/* --------------------------------------------------------------------------
CAUTION
@@ -1584,13 +1585,6 @@ new_threadstate(PyInterpreterState *interp, int whence)
PyMem_RawFree(new_tstate);
}
else {
-#ifdef Py_GIL_DISABLED
- if (_Py_atomic_load_int(&interp->gc.immortalize) == 0) {
- // Immortalize objects marked as using deferred reference counting
- // the first time a non-main thread is created.
- _PyGC_ImmortalizeDeferredObjects(interp);
- }
-#endif
}
#ifdef Py_GIL_DISABLED
@@ -1741,6 +1735,10 @@ PyThreadState_Clear(PyThreadState *tstate)
struct _Py_freelists *freelists = _Py_freelists_GET();
_PyObject_ClearFreeLists(freelists, 1);
+ // Merge our thread-local refcounts into the type's own refcount and
+ // free our local refcount array.
+ _PyType_FinalizeThreadLocalRefcounts((_PyThreadStateImpl *)tstate);
+
// Remove ourself from the biased reference counting table of threads.
_Py_brc_remove_thread(tstate);
#endif
@@ -1799,6 +1797,7 @@ tstate_delete_common(PyThreadState *tstate, int release_gil)
_PyThreadStateImpl *tstate_impl = (_PyThreadStateImpl *)tstate;
tstate->interp->object_state.reftotal += tstate_impl->reftotal;
tstate_impl->reftotal = 0;
+ assert(tstate_impl->types.refcounts == NULL);
#endif
HEAD_UNLOCK(runtime);
diff --git a/Python/typeid.c b/Python/typeid.c
new file mode 100644
index 00000000000..83a68723ded
--- /dev/null
+++ b/Python/typeid.c
@@ -0,0 +1,200 @@
+#include "Python.h"
+
+#include "pycore_lock.h" // PyMutex_LockFlags()
+#include "pycore_pystate.h" // _PyThreadState_GET()
+#include "pycore_object.h" // _Py_IncRefTotal
+#include "pycore_typeid.h"
+
+// This contains code for allocating unique ids to heap type objects
+// and re-using those ids when the type is deallocated.
+//
+// See Include/internal/pycore_typeid.h for more details.
+
+#ifdef Py_GIL_DISABLED
+
+#define POOL_MIN_SIZE 8
+
+#define LOCK_POOL(pool) PyMutex_LockFlags(&pool->mutex, _Py_LOCK_DONT_DETACH)
+#define UNLOCK_POOL(pool) PyMutex_Unlock(&pool->mutex)
+
+static int
+resize_interp_type_id_pool(struct _Py_type_id_pool *pool)
+{
+ if ((size_t)pool->size > PY_SSIZE_T_MAX / (2 * sizeof(*pool->table))) {
+ return -1;
+ }
+
+ Py_ssize_t new_size = pool->size * 2;
+ if (new_size < POOL_MIN_SIZE) {
+ new_size = POOL_MIN_SIZE;
+ }
+
+ _Py_type_id_entry *table = PyMem_Realloc(pool->table,
+ new_size * sizeof(*pool->table));
+ if (table == NULL) {
+ return -1;
+ }
+
+ Py_ssize_t start = pool->size;
+ for (Py_ssize_t i = start; i < new_size - 1; i++) {
+ table[i].next = &table[i + 1];
+ }
+ table[new_size - 1].next = NULL;
+
+ pool->table = table;
+ pool->freelist = &table[start];
+ _Py_atomic_store_ssize(&pool->size, new_size);
+ return 0;
+}
+
+static int
+resize_local_refcounts(_PyThreadStateImpl *tstate)
+{
+ if (tstate->types.is_finalized) {
+ return -1;
+ }
+
+ struct _Py_type_id_pool *pool = &tstate->base.interp->type_ids;
+ Py_ssize_t size = _Py_atomic_load_ssize(&pool->size);
+
+ Py_ssize_t *refcnts = PyMem_Realloc(tstate->types.refcounts,
+ size * sizeof(Py_ssize_t));
+ if (refcnts == NULL) {
+ return -1;
+ }
+
+ Py_ssize_t old_size = tstate->types.size;
+ if (old_size < size) {
+ memset(refcnts + old_size, 0, (size - old_size) * sizeof(Py_ssize_t));
+ }
+
+ tstate->types.refcounts = refcnts;
+ tstate->types.size = size;
+ return 0;
+}
+
+void
+_PyType_AssignId(PyHeapTypeObject *type)
+{
+ PyInterpreterState *interp = _PyInterpreterState_GET();
+ struct _Py_type_id_pool *pool = &interp->type_ids;
+
+ LOCK_POOL(pool);
+ if (pool->freelist == NULL) {
+ if (resize_interp_type_id_pool(pool) < 0) {
+ type->unique_id = -1;
+ UNLOCK_POOL(pool);
+ return;
+ }
+ }
+
+ _Py_type_id_entry *entry = pool->freelist;
+ pool->freelist = entry->next;
+ entry->type = type;
+ _PyObject_SetDeferredRefcount((PyObject *)type);
+ type->unique_id = (entry - pool->table);
+ UNLOCK_POOL(pool);
+}
+
+void
+_PyType_ReleaseId(PyHeapTypeObject *type)
+{
+ PyInterpreterState *interp = _PyInterpreterState_GET();
+ struct _Py_type_id_pool *pool = &interp->type_ids;
+
+ if (type->unique_id < 0) {
+ // The type doesn't have an id assigned.
+ return;
+ }
+
+ LOCK_POOL(pool);
+ _Py_type_id_entry *entry = &pool->table[type->unique_id];
+ assert(entry->type == type);
+ entry->next = pool->freelist;
+ pool->freelist = entry;
+
+ type->unique_id = -1;
+ UNLOCK_POOL(pool);
+}
+
+void
+_PyType_IncrefSlow(PyHeapTypeObject *type)
+{
+ _PyThreadStateImpl *tstate = (_PyThreadStateImpl *)_PyThreadState_GET();
+ if (type->unique_id < 0 || resize_local_refcounts(tstate) < 0) {
+ // just incref the type directly.
+ Py_INCREF(type);
+ return;
+ }
+
+ assert(type->unique_id < tstate->types.size);
+ tstate->types.refcounts[type->unique_id]++;
+#ifdef Py_REF_DEBUG
+ _Py_IncRefTotal((PyThreadState *)tstate);
+#endif
+ _Py_INCREF_STAT_INC();
+}
+
+void
+_PyType_MergeThreadLocalRefcounts(_PyThreadStateImpl *tstate)
+{
+ if (tstate->types.refcounts == NULL) {
+ return;
+ }
+
+ struct _Py_type_id_pool *pool = &tstate->base.interp->type_ids;
+
+ LOCK_POOL(pool);
+ for (Py_ssize_t i = 0, n = tstate->types.size; i < n; i++) {
+ Py_ssize_t refcnt = tstate->types.refcounts[i];
+ if (refcnt != 0) {
+ PyObject *type = (PyObject *)pool->table[i].type;
+ assert(PyType_Check(type));
+
+ _Py_atomic_add_ssize(&type->ob_ref_shared,
+ refcnt << _Py_REF_SHARED_SHIFT);
+ tstate->types.refcounts[i] = 0;
+ }
+ }
+ UNLOCK_POOL(pool);
+}
+
+void
+_PyType_FinalizeThreadLocalRefcounts(_PyThreadStateImpl *tstate)
+{
+ _PyType_MergeThreadLocalRefcounts(tstate);
+
+ PyMem_Free(tstate->types.refcounts);
+ tstate->types.refcounts = NULL;
+ tstate->types.size = 0;
+ tstate->types.is_finalized = 1;
+}
+
+void
+_PyType_FinalizeIdPool(PyInterpreterState *interp)
+{
+ struct _Py_type_id_pool *pool = &interp->type_ids;
+
+ // First, set the free-list to NULL values
+ while (pool->freelist) {
+ _Py_type_id_entry *next = pool->freelist->next;
+ pool->freelist->type = NULL;
+ pool->freelist = next;
+ }
+
+ // Now everything non-NULL is a type. Set the type's id to -1 in case it
+ // outlives the interpreter.
+ for (Py_ssize_t i = 0; i < pool->size; i++) {
+ PyHeapTypeObject *ht = pool->table[i].type;
+ if (ht) {
+ ht->unique_id = -1;
+ pool->table[i].type = NULL;
+ }
+ }
+ PyMem_Free(pool->table);
+ pool->table = NULL;
+ pool->freelist = NULL;
+ pool->size = 0;
+}
+
+#endif /* Py_GIL_DISABLED */