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bpo-40521: Disable method cache in subinterpreters #19960

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May 6, 2020
Merged

bpo-40521: Disable method cache in subinterpreters #19960

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22 changes: 19 additions & 3 deletions Objects/typeobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,12 @@ class object "PyObject *" "&PyBaseObject_Type"

#include "clinic/typeobject.c.h"

/* bpo-40521: Type method cache is shared by all subinterpreters */
#ifndef EXPERIMENTAL_ISOLATED_SUBINTERPRETERS
# define MCACHE
#endif

#ifdef MCACHE
/* Support type attribute cache */

/* The cache can keep references to the names alive for longer than
Expand Down Expand Up @@ -47,6 +53,7 @@ struct method_cache_entry {

static struct method_cache_entry method_cache[1 << MCACHE_SIZE_EXP];
static unsigned int next_version_tag = 0;
#endif

#define MCACHE_STATS 0

Expand Down Expand Up @@ -216,6 +223,7 @@ _PyType_GetTextSignatureFromInternalDoc(const char *name, const char *internal_d
unsigned int
PyType_ClearCache(void)
{
#ifdef MCACHE
Py_ssize_t i;
unsigned int cur_version_tag = next_version_tag - 1;

Expand All @@ -240,6 +248,9 @@ PyType_ClearCache(void)
/* mark all version tags as invalid */
PyType_Modified(&PyBaseObject_Type);
return cur_version_tag;
#else
return 0;
#endif
}

void
Expand Down Expand Up @@ -350,6 +361,7 @@ type_mro_modified(PyTypeObject *type, PyObject *bases) {
Py_TPFLAGS_VALID_VERSION_TAG);
}

#ifdef MCACHE
static int
assign_version_tag(PyTypeObject *type)
{
Expand Down Expand Up @@ -396,6 +408,7 @@ assign_version_tag(PyTypeObject *type)
type->tp_flags |= Py_TPFLAGS_VALID_VERSION_TAG;
return 1;
}
#endif


static PyMemberDef type_members[] = {
Expand Down Expand Up @@ -3232,12 +3245,12 @@ _PyType_Lookup(PyTypeObject *type, PyObject *name)
{
PyObject *res;
int error;
unsigned int h;

#ifdef MCACHE
if (MCACHE_CACHEABLE_NAME(name) &&
_PyType_HasFeature(type, Py_TPFLAGS_VALID_VERSION_TAG)) {
/* fast path */
h = MCACHE_HASH_METHOD(type, name);
unsigned int h = MCACHE_HASH_METHOD(type, name);
if (method_cache[h].version == type->tp_version_tag &&
method_cache[h].name == name) {
#if MCACHE_STATS
Expand All @@ -3246,6 +3259,7 @@ _PyType_Lookup(PyTypeObject *type, PyObject *name)
return method_cache[h].value;
}
}
#endif

/* We may end up clearing live exceptions below, so make sure it's ours. */
assert(!PyErr_Occurred());
Expand All @@ -3267,8 +3281,9 @@ _PyType_Lookup(PyTypeObject *type, PyObject *name)
return NULL;
}

#ifdef MCACHE
if (MCACHE_CACHEABLE_NAME(name) && assign_version_tag(type)) {
h = MCACHE_HASH_METHOD(type, name);
unsigned int h = MCACHE_HASH_METHOD(type, name);
method_cache[h].version = type->tp_version_tag;
method_cache[h].value = res; /* borrowed */
Py_INCREF(name);
Expand All @@ -3281,6 +3296,7 @@ _PyType_Lookup(PyTypeObject *type, PyObject *name)
#endif
Py_SETREF(method_cache[h].name, name);
}
#endif
return res;
}

Expand Down