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bpo-40521: Disable free lists in subinterpreters (GH-19937)
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When Python is built with experimental isolated interpreters, disable
tuple, dict and free free lists.

Temporary workaround until these caches are made per-interpreter.

Add frame_alloc() and frame_get_builtins() subfunctions to simplify
_PyFrame_New_NoTrack().
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@vstinner
vstinner authored May 5, 2020
1 parent ac4bf42 commit b4b5386
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Showing 3 changed files with 162 additions and 80 deletions.
37 changes: 33 additions & 4 deletions Objects/dictobject.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -250,16 +250,26 @@ static uint64_t pydict_global_version = 0;
#ifndef PyDict_MAXFREELIST
#define PyDict_MAXFREELIST 80
#endif

/* bpo-40521: dict free lists are shared by all interpreters. */
#ifdef EXPERIMENTAL_ISOLATED_SUBINTERPRETERS
# undef PyDict_MAXFREELIST
# define PyDict_MAXFREELIST 0
#endif

#if PyDict_MAXFREELIST > 0
static PyDictObject *free_list[PyDict_MAXFREELIST];
static int numfree = 0;
static PyDictKeysObject *keys_free_list[PyDict_MAXFREELIST];
static int numfreekeys = 0;
#endif

#include "clinic/dictobject.c.h"

void
_PyDict_ClearFreeList(void)
{
#if PyDict_MAXFREELIST > 0
while (numfree) {
PyDictObject *op = free_list[--numfree];
assert(PyDict_CheckExact(op));
Expand All @@ -268,14 +278,17 @@ _PyDict_ClearFreeList(void)
while (numfreekeys) {
PyObject_FREE(keys_free_list[--numfreekeys]);
}
#endif
}

/* Print summary info about the state of the optimized allocator */
void
_PyDict_DebugMallocStats(FILE *out)
{
#if PyDict_MAXFREELIST > 0
_PyDebugAllocatorStats(out,
"free PyDictObject", numfree, sizeof(PyDictObject));
#endif
}


Expand Down Expand Up @@ -553,10 +566,13 @@ static PyDictKeysObject *new_keys_object(Py_ssize_t size)
es = sizeof(Py_ssize_t);
}

#if PyDict_MAXFREELIST > 0
if (size == PyDict_MINSIZE && numfreekeys > 0) {
dk = keys_free_list[--numfreekeys];
}
else {
else
#endif
{
dk = PyObject_MALLOC(sizeof(PyDictKeysObject)
+ es * size
+ sizeof(PyDictKeyEntry) * usable);
Expand Down Expand Up @@ -587,10 +603,12 @@ free_keys_object(PyDictKeysObject *keys)
Py_XDECREF(entries[i].me_key);
Py_XDECREF(entries[i].me_value);
}
#if PyDict_MAXFREELIST > 0
if (keys->dk_size == PyDict_MINSIZE && numfreekeys < PyDict_MAXFREELIST) {
keys_free_list[numfreekeys++] = keys;
return;
}
#endif
PyObject_FREE(keys);
}

Expand All @@ -603,13 +621,16 @@ new_dict(PyDictKeysObject *keys, PyObject **values)
{
PyDictObject *mp;
assert(keys != NULL);
#if PyDict_MAXFREELIST > 0
if (numfree) {
mp = free_list[--numfree];
assert (mp != NULL);
assert (Py_IS_TYPE(mp, &PyDict_Type));
_Py_NewReference((PyObject *)mp);
}
else {
else
#endif
{
mp = PyObject_GC_New(PyDictObject, &PyDict_Type);
if (mp == NULL) {
dictkeys_decref(keys);
Expand Down Expand Up @@ -1258,12 +1279,15 @@ dictresize(PyDictObject *mp, Py_ssize_t minsize)
#ifdef Py_REF_DEBUG
_Py_RefTotal--;
#endif
#if PyDict_MAXFREELIST > 0
if (oldkeys->dk_size == PyDict_MINSIZE &&
numfreekeys < PyDict_MAXFREELIST)
{
keys_free_list[numfreekeys++] = oldkeys;
}
else {
else
#endif
{
PyObject_FREE(oldkeys);
}
}
Expand Down Expand Up @@ -2005,10 +2029,15 @@ dict_dealloc(PyDictObject *mp)
assert(keys->dk_refcnt == 1);
dictkeys_decref(keys);
}
if (numfree < PyDict_MAXFREELIST && Py_IS_TYPE(mp, &PyDict_Type))
#if PyDict_MAXFREELIST > 0
if (numfree < PyDict_MAXFREELIST && Py_IS_TYPE(mp, &PyDict_Type)) {
free_list[numfree++] = mp;
}
else
#endif
{
Py_TYPE(mp)->tp_free((PyObject *)mp);
}
Py_TRASHCAN_END
}

Expand Down
197 changes: 121 additions & 76 deletions Objects/frameobject.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -556,11 +556,19 @@ static PyGetSetDef frame_getsetlist[] = {
free_list. Else programs creating lots of cyclic trash involving
frames could provoke free_list into growing without bound.
*/
/* max value for numfree */
#define PyFrame_MAXFREELIST 200

/* bpo-40521: frame free lists are shared by all interpreters. */
#ifdef EXPERIMENTAL_ISOLATED_SUBINTERPRETERS
# undef PyFrame_MAXFREELIST
# define PyFrame_MAXFREELIST 0
#endif

#if PyFrame_MAXFREELIST > 0
static PyFrameObject *free_list = NULL;
static int numfree = 0; /* number of frames currently in free_list */
/* max value for numfree */
#define PyFrame_MAXFREELIST 200
#endif

static void _Py_HOT_FUNCTION
frame_dealloc(PyFrameObject *f)
Expand Down Expand Up @@ -590,15 +598,19 @@ frame_dealloc(PyFrameObject *f)
Py_CLEAR(f->f_trace);

co = f->f_code;
if (co->co_zombieframe == NULL)
if (co->co_zombieframe == NULL) {
co->co_zombieframe = f;
}
#if PyFrame_MAXFREELIST > 0
else if (numfree < PyFrame_MAXFREELIST) {
++numfree;
f->f_back = free_list;
free_list = f;
}
else
#endif
else {
PyObject_GC_Del(f);
}

Py_DECREF(co);
Py_TRASHCAN_SAFE_END(f)
Expand Down Expand Up @@ -759,98 +771,127 @@ PyTypeObject PyFrame_Type = {

_Py_IDENTIFIER(__builtins__);

PyFrameObject* _Py_HOT_FUNCTION
_PyFrame_New_NoTrack(PyThreadState *tstate, PyCodeObject *code,
PyObject *globals, PyObject *locals)
static inline PyFrameObject*
frame_alloc(PyCodeObject *code)
{
PyFrameObject *back = tstate->frame;
PyFrameObject *f;
PyObject *builtins;
Py_ssize_t i;

#ifdef Py_DEBUG
if (code == NULL || globals == NULL || !PyDict_Check(globals) ||
(locals != NULL && !PyMapping_Check(locals))) {
PyErr_BadInternalCall();
return NULL;
f = code->co_zombieframe;
if (f != NULL) {
code->co_zombieframe = NULL;
_Py_NewReference((PyObject *)f);
assert(f->f_code == code);
return f;
}

Py_ssize_t ncells = PyTuple_GET_SIZE(code->co_cellvars);
Py_ssize_t nfrees = PyTuple_GET_SIZE(code->co_freevars);
Py_ssize_t extras = code->co_stacksize + code->co_nlocals + ncells + nfrees;
#if PyFrame_MAXFREELIST > 0
if (free_list == NULL)
#endif
if (back == NULL || back->f_globals != globals) {
builtins = _PyDict_GetItemIdWithError(globals, &PyId___builtins__);
if (builtins) {
if (PyModule_Check(builtins)) {
builtins = PyModule_GetDict(builtins);
assert(builtins != NULL);
}
{
f = PyObject_GC_NewVar(PyFrameObject, &PyFrame_Type, extras);
if (f == NULL) {
return NULL;
}
if (builtins == NULL) {
if (PyErr_Occurred()) {
}
#if PyFrame_MAXFREELIST > 0
else {
assert(numfree > 0);
--numfree;
f = free_list;
free_list = free_list->f_back;
if (Py_SIZE(f) < extras) {
PyFrameObject *new_f = PyObject_GC_Resize(PyFrameObject, f, extras);
if (new_f == NULL) {
PyObject_GC_Del(f);
return NULL;
}
/* No builtins! Make up a minimal one
Give them 'None', at least. */
builtins = PyDict_New();
if (builtins == NULL ||
PyDict_SetItemString(
builtins, "None", Py_None) < 0)
return NULL;
f = new_f;
}
else
Py_INCREF(builtins);
_Py_NewReference((PyObject *)f);
}
#endif

f->f_code = code;
extras = code->co_nlocals + ncells + nfrees;
f->f_valuestack = f->f_localsplus + extras;
for (Py_ssize_t i=0; i<extras; i++) {
f->f_localsplus[i] = NULL;
}
else {
f->f_locals = NULL;
f->f_trace = NULL;
return f;
}


static inline PyObject *
frame_get_builtins(PyFrameObject *back, PyObject *globals)
{
PyObject *builtins;

if (back != NULL && back->f_globals == globals) {
/* If we share the globals, we share the builtins.
Save a lookup and a call. */
builtins = back->f_builtins;
assert(builtins != NULL);
Py_INCREF(builtins);
return builtins;
}
if (code->co_zombieframe != NULL) {
f = code->co_zombieframe;
code->co_zombieframe = NULL;
_Py_NewReference((PyObject *)f);
assert(f->f_code == code);

builtins = _PyDict_GetItemIdWithError(globals, &PyId___builtins__);
if (builtins != NULL && PyModule_Check(builtins)) {
builtins = PyModule_GetDict(builtins);
assert(builtins != NULL);
}
else {
Py_ssize_t extras, ncells, nfrees;
ncells = PyTuple_GET_SIZE(code->co_cellvars);
nfrees = PyTuple_GET_SIZE(code->co_freevars);
extras = code->co_stacksize + code->co_nlocals + ncells +
nfrees;
if (free_list == NULL) {
f = PyObject_GC_NewVar(PyFrameObject, &PyFrame_Type,
extras);
if (f == NULL) {
Py_DECREF(builtins);
return NULL;
}
}
else {
assert(numfree > 0);
--numfree;
f = free_list;
free_list = free_list->f_back;
if (Py_SIZE(f) < extras) {
PyFrameObject *new_f = PyObject_GC_Resize(PyFrameObject, f, extras);
if (new_f == NULL) {
PyObject_GC_Del(f);
Py_DECREF(builtins);
return NULL;
}
f = new_f;
}
_Py_NewReference((PyObject *)f);
}
if (builtins != NULL) {
Py_INCREF(builtins);
return builtins;
}

if (PyErr_Occurred()) {
return NULL;
}

/* No builtins! Make up a minimal one.
Give them 'None', at least. */
builtins = PyDict_New();
if (builtins == NULL) {
return NULL;
}
if (PyDict_SetItemString(builtins, "None", Py_None) < 0) {
Py_DECREF(builtins);
return NULL;
}
return builtins;
}

f->f_code = code;
extras = code->co_nlocals + ncells + nfrees;
f->f_valuestack = f->f_localsplus + extras;
for (i=0; i<extras; i++)
f->f_localsplus[i] = NULL;
f->f_locals = NULL;
f->f_trace = NULL;

PyFrameObject* _Py_HOT_FUNCTION
_PyFrame_New_NoTrack(PyThreadState *tstate, PyCodeObject *code,
PyObject *globals, PyObject *locals)
{
#ifdef Py_DEBUG
if (code == NULL || globals == NULL || !PyDict_Check(globals) ||
(locals != NULL && !PyMapping_Check(locals))) {
PyErr_BadInternalCall();
return NULL;
}
#endif

PyFrameObject *back = tstate->frame;
PyObject *builtins = frame_get_builtins(back, globals);
if (builtins == NULL) {
return NULL;
}

PyFrameObject *f = frame_alloc(code);
if (f == NULL) {
Py_DECREF(builtins);
return NULL;
}

f->f_stacktop = f->f_valuestack;
f->f_builtins = builtins;
Py_XINCREF(back);
Expand Down Expand Up @@ -1142,13 +1183,15 @@ PyFrame_LocalsToFast(PyFrameObject *f, int clear)
void
_PyFrame_ClearFreeList(void)
{
#if PyFrame_MAXFREELIST > 0
while (free_list != NULL) {
PyFrameObject *f = free_list;
free_list = free_list->f_back;
PyObject_GC_Del(f);
--numfree;
}
assert(numfree == 0);
#endif
}

void
Expand All @@ -1161,9 +1204,11 @@ _PyFrame_Fini(void)
void
_PyFrame_DebugMallocStats(FILE *out)
{
#if PyFrame_MAXFREELIST > 0
_PyDebugAllocatorStats(out,
"free PyFrameObject",
numfree, sizeof(PyFrameObject));
#endif
}


Expand Down
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