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gh-124218: Use per-thread reference counting for globals and builtins #125713

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merged 3 commits into from
Oct 21, 2024
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gh-124218: Use per-thread reference counting for globals and builtins #125713

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568d6b9
gh-124218: Use per-thread reference counting for globals and builtins
colesbury Oct 15, 2024
17653fd
Changes from review:
colesbury Oct 21, 2024
50813b4
Fix shift of id on 32-bit platforms
colesbury Oct 21, 2024
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33 changes: 33 additions & 0 deletions Include/internal/pycore_dict.h
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Original file line number Diff line number Diff line change
Expand Up @@ -229,6 +229,8 @@ static inline PyDictUnicodeEntry* DK_UNICODE_ENTRIES(PyDictKeysObject *dk) {
#define DICT_VERSION_INCREMENT (1 << (DICT_MAX_WATCHERS + DICT_WATCHED_MUTATION_BITS))
#define DICT_WATCHER_MASK ((1 << DICT_MAX_WATCHERS) - 1)
#define DICT_WATCHER_AND_MODIFICATION_MASK ((1 << (DICT_MAX_WATCHERS + DICT_WATCHED_MUTATION_BITS)) - 1)
#define DICT_UNIQUE_ID_SHIFT (DICT_MAX_WATCHERS + DICT_WATCHED_MUTATION_BITS)
#define DICT_UNIQUE_ID_MAX (UINT64_MAX >> DICT_UNIQUE_ID_SHIFT)


PyAPI_FUNC(void)
Expand Down Expand Up @@ -307,8 +309,39 @@ _PyInlineValuesSize(PyTypeObject *tp)
int
_PyDict_DetachFromObject(PyDictObject *dict, PyObject *obj);

// Enables per-thread ref counting on this dict in the free threading build
extern void _PyDict_EnablePerThreadRefcounting(PyObject *op);

PyDictObject *_PyObject_MaterializeManagedDict_LockHeld(PyObject *);

#ifndef Py_GIL_DISABLED
# define _Py_INCREF_DICT Py_INCREF
# define _Py_DECREF_DICT Py_DECREF
#else
static inline Py_ssize_t
_PyDict_UniqueId(PyDictObject *mp)
{
// Offset by on so that _ma_watcher_tag=0 represents an unassigned id
return (Py_ssize_t)(mp->_ma_watcher_tag >> DICT_UNIQUE_ID_SHIFT) - 1;
}

static inline void
_Py_INCREF_DICT(PyObject *op)
{
assert(PyDict_Check(op));
Py_ssize_t id = _PyDict_UniqueId((PyDictObject *)op);
_Py_THREAD_INCREF_OBJECT(op, id);
}

static inline void
_Py_DECREF_DICT(PyObject *op)
{
assert(PyDict_Check(op));
Py_ssize_t id = _PyDict_UniqueId((PyDictObject *)op);
_Py_THREAD_DECREF_OBJECT(op, id);
}
#endif

#ifdef __cplusplus
}
#endif
Expand Down
14 changes: 14 additions & 0 deletions Objects/dictobject.c
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Expand Up @@ -1636,6 +1636,20 @@ _PyDict_MaybeUntrack(PyObject *op)
_PyObject_GC_UNTRACK(op);
}

void
_PyDict_EnablePerThreadRefcounting(PyObject *op)
{
assert(PyDict_Check(op));
#ifdef Py_GIL_DISABLED
Py_ssize_t id = _PyObject_AssignUniqueId(op);

PyDictObject *mp = (PyDictObject *)op;
assert((mp->_ma_watcher_tag >> DICT_UNIQUE_ID_SHIFT) == 0);
// Plus 1 so that _ma_watcher_tag=0 represents an unassigned id
mp->_ma_watcher_tag += (id + 1) << DICT_UNIQUE_ID_SHIFT;
#endif
}

static inline int
is_unusable_slot(Py_ssize_t ix)
{
Expand Down
38 changes: 32 additions & 6 deletions Objects/funcobject.c
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Expand Up @@ -3,6 +3,7 @@

#include "Python.h"
#include "pycore_ceval.h" // _PyEval_BuiltinsFromGlobals()
#include "pycore_dict.h" // _Py_INCREF_DICT()
#include "pycore_long.h" // _PyLong_GetOne()
#include "pycore_modsupport.h" // _PyArg_NoKeywords()
#include "pycore_object.h" // _PyObject_GC_UNTRACK()
Expand Down Expand Up @@ -112,8 +113,15 @@ _PyFunction_FromConstructor(PyFrameConstructor *constr)
Py_XDECREF(module);
return NULL;
}
op->func_globals = Py_NewRef(constr->fc_globals);
op->func_builtins = Py_NewRef(constr->fc_builtins);
_Py_INCREF_DICT(constr->fc_globals);
op->func_globals = constr->fc_globals;
if (PyDict_Check(constr->fc_builtins)) {
_Py_INCREF_DICT(constr->fc_builtins);
}
else {
Py_INCREF(constr->fc_builtins);
}
op->func_builtins = constr->fc_builtins;
op->func_name = Py_NewRef(constr->fc_name);
op->func_qualname = Py_NewRef(constr->fc_qualname);
_Py_INCREF_CODE((PyCodeObject *)constr->fc_code);
Expand Down Expand Up @@ -143,7 +151,7 @@ PyFunction_NewWithQualName(PyObject *code, PyObject *globals, PyObject *qualname
{
assert(globals != NULL);
assert(PyDict_Check(globals));
Py_INCREF(globals);
_Py_INCREF_DICT(globals);

PyThreadState *tstate = _PyThreadState_GET();

Expand Down Expand Up @@ -184,7 +192,12 @@ PyFunction_NewWithQualName(PyObject *code, PyObject *globals, PyObject *qualname
if (builtins == NULL) {
goto error;
}
Py_INCREF(builtins);
if (PyDict_Check(builtins)) {
_Py_INCREF_DICT(builtins);
}
else {
Py_INCREF(builtins);
}

PyFunctionObject *op = PyObject_GC_New(PyFunctionObject, &PyFunction_Type);
if (op == NULL) {
Expand Down Expand Up @@ -1057,8 +1070,21 @@ func_clear(PyObject *self)
{
PyFunctionObject *op = _PyFunction_CAST(self);
func_clear_version(_PyInterpreterState_GET(), op);
Py_CLEAR(op->func_globals);
Py_CLEAR(op->func_builtins);
PyObject *globals = op->func_globals;
op->func_globals = NULL;
if (globals != NULL) {
_Py_DECREF_DICT(globals);
}
PyObject *builtins = op->func_builtins;
op->func_builtins = NULL;
if (builtins != NULL) {
if (PyDict_Check(builtins)) {
_Py_DECREF_DICT(builtins);
}
else {
Py_DECREF(builtins);
}
}
Py_CLEAR(op->func_module);
Py_CLEAR(op->func_defaults);
Py_CLEAR(op->func_kwdefaults);
Expand Down
3 changes: 2 additions & 1 deletion Objects/moduleobject.c
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Expand Up @@ -3,6 +3,7 @@

#include "Python.h"
#include "pycore_call.h" // _PyObject_CallNoArgs()
#include "pycore_dict.h" // _PyDict_EnablePerThreadRefcounting()
#include "pycore_fileutils.h" // _Py_wgetcwd
#include "pycore_interp.h" // PyInterpreterState.importlib
#include "pycore_long.h" // _PyLong_GetOne()
Expand Down Expand Up @@ -105,7 +106,7 @@ new_module_notrack(PyTypeObject *mt)
static void
track_module(PyModuleObject *m)
{
_PyObject_SetDeferredRefcount(m->md_dict);
_PyDict_EnablePerThreadRefcounting(m->md_dict);
PyObject_GC_Track(m->md_dict);

_PyObject_SetDeferredRefcount((PyObject *)m);
Expand Down
13 changes: 12 additions & 1 deletion Python/uniqueid.c
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@@ -1,5 +1,6 @@
#include "Python.h"

#include "pycore_dict.h" // DICT_UNIQUE_ID_MAX
#include "pycore_lock.h" // PyMutex_LockFlags()
#include "pycore_pystate.h" // _PyThreadState_GET()
#include "pycore_object.h" // _Py_IncRefTotal
Expand Down Expand Up @@ -90,10 +91,15 @@ _PyObject_AssignUniqueId(PyObject *obj)
}

_Py_unique_id_entry *entry = pool->freelist;
Py_ssize_t unique_id = (entry - pool->table);
if ((uint64_t)unique_id >= DICT_UNIQUE_ID_MAX) {
UNLOCK_POOL(pool);
return -1;
}

pool->freelist = entry->next;
entry->obj = obj;
_PyObject_SetDeferredRefcount(obj);
Py_ssize_t unique_id = (entry - pool->table);
UNLOCK_POOL(pool);
return unique_id;
}
Expand Down Expand Up @@ -128,6 +134,11 @@ clear_unique_id(PyObject *obj)
id = co->_co_unique_id;
co->_co_unique_id = -1;
}
else if (PyDict_Check(obj)) {
PyDictObject *mp = (PyDictObject *)obj;
id = _PyDict_UniqueId(mp);
mp->_ma_watcher_tag &= ~(UINT64_MAX << DICT_UNIQUE_ID_SHIFT);
}
return id;
}

Expand Down
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