bpo-40521: Make empty Unicode string per interpreter (GH-21096)
Each interpreter now has its own empty Unicode string singleton.
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 1433848..06ca7a5 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -222,26 +222,43 @@
static PyObject *interned = NULL;
#endif
-/* The empty Unicode object is shared to improve performance. */
-static PyObject *unicode_empty = NULL;
+static struct _Py_unicode_state*
+get_unicode_state(void)
+{
+ PyInterpreterState *interp = _PyInterpreterState_GET();
+ return &interp->unicode;
+}
-#define _Py_INCREF_UNICODE_EMPTY() \
- do { \
- if (unicode_empty != NULL) \
- Py_INCREF(unicode_empty); \
- else { \
- unicode_empty = PyUnicode_New(0, 0); \
- if (unicode_empty != NULL) { \
- Py_INCREF(unicode_empty); \
- assert(_PyUnicode_CheckConsistency(unicode_empty, 1)); \
- } \
- } \
- } while (0)
-#define _Py_RETURN_UNICODE_EMPTY() \
- do { \
- _Py_INCREF_UNICODE_EMPTY(); \
- return unicode_empty; \
+// Return a borrowed reference to the empty string singleton.
+// Return NULL if the singleton was not created yet.
+static inline PyObject* unicode_get_empty(void)
+{
+ struct _Py_unicode_state *state = get_unicode_state();
+ return state->empty;
+}
+
+static inline PyObject* unicode_new_empty(void)
+{
+ struct _Py_unicode_state *state = get_unicode_state();
+ PyObject *empty = state->empty;
+ if (empty != NULL) {
+ Py_INCREF(empty);
+ }
+ else {
+ empty = PyUnicode_New(0, 0);
+ if (empty != NULL) {
+ Py_INCREF(empty);
+ assert(_PyUnicode_CheckConsistency(empty, 1));
+ state->empty = empty;
+ }
+ }
+ return empty;
+}
+
+#define _Py_RETURN_UNICODE_EMPTY() \
+ do { \
+ return unicode_new_empty(); \
} while (0)
static inline void
@@ -676,11 +693,15 @@
length = PyUnicode_GET_LENGTH(unicode);
if (length == 0) {
- if (unicode != unicode_empty) {
+ PyObject *empty = unicode_get_empty();
+ if (unicode != empty) {
Py_DECREF(unicode);
- _Py_RETURN_UNICODE_EMPTY();
+
+ Py_INCREF(empty);
+ return empty;
}
- return unicode_empty;
+ // unicode is the empty string singleton
+ return unicode;
}
#ifdef LATIN1_SINGLETONS
@@ -864,7 +885,7 @@
to keep things simple, we use a single bitmask, using the least 5
bits from each unicode characters as the bit index. */
-/* the linebreak mask is set up by Unicode_Init below */
+/* the linebreak mask is set up by _PyUnicode_Init() below */
#if LONG_BIT >= 128
#define BLOOM_WIDTH 128
@@ -938,6 +959,8 @@
/* Compilation of templated routines */
+#define STRINGLIB_GET_EMPTY() unicode_get_empty()
+
#include "stringlib/asciilib.h"
#include "stringlib/fastsearch.h"
#include "stringlib/partition.h"
@@ -986,6 +1009,8 @@
#include "stringlib/undef.h"
_Py_COMP_DIAG_POP
+#undef STRINGLIB_GET_EMPTY
+
/* --- Unicode Object ----------------------------------------------------- */
static inline Py_ssize_t
@@ -1234,9 +1259,12 @@
size_t new_size;
/* Optimization for empty strings */
- if (length == 0 && unicode_empty != NULL) {
- Py_INCREF(unicode_empty);
- return (PyUnicodeObject*)unicode_empty;
+ if (length == 0) {
+ PyObject *empty = unicode_get_empty();
+ if (empty != NULL) {
+ Py_INCREF(empty);
+ return (PyUnicodeObject *)empty;
+ }
}
/* Ensure we won't overflow the size. */
@@ -1386,6 +1414,15 @@
PyObject *
PyUnicode_New(Py_ssize_t size, Py_UCS4 maxchar)
{
+ /* Optimization for empty strings */
+ if (size == 0) {
+ PyObject *empty = unicode_get_empty();
+ if (empty != NULL) {
+ Py_INCREF(empty);
+ return empty;
+ }
+ }
+
PyObject *obj;
PyCompactUnicodeObject *unicode;
void *data;
@@ -1394,12 +1431,6 @@
Py_ssize_t char_size;
Py_ssize_t struct_size;
- /* Optimization for empty strings */
- if (size == 0 && unicode_empty != NULL) {
- Py_INCREF(unicode_empty);
- return unicode_empty;
- }
-
is_ascii = 0;
is_sharing = 0;
struct_size = sizeof(PyCompactUnicodeObject);
@@ -1970,7 +2001,8 @@
static int
unicode_is_singleton(PyObject *unicode)
{
- if (unicode == unicode_empty) {
+ struct _Py_unicode_state *state = get_unicode_state();
+ if (unicode == state->empty) {
return 1;
}
#ifdef LATIN1_SINGLETONS
@@ -2026,10 +2058,10 @@
return 0;
if (length == 0) {
- _Py_INCREF_UNICODE_EMPTY();
- if (!unicode_empty)
+ PyObject *empty = unicode_new_empty();
+ if (!empty)
return -1;
- Py_SETREF(*p_unicode, unicode_empty);
+ Py_SETREF(*p_unicode, empty);
return 0;
}
@@ -10836,10 +10868,10 @@
}
new_size = slen + n * (len2 - len1);
if (new_size == 0) {
- _Py_INCREF_UNICODE_EMPTY();
- if (!unicode_empty)
+ PyObject *empty = unicode_new_empty();
+ if (!empty)
goto error;
- u = unicode_empty;
+ u = empty;
goto done;
}
if (new_size > (PY_SSIZE_T_MAX / rkind)) {
@@ -11497,10 +11529,13 @@
return NULL;
/* Shortcuts */
- if (left == unicode_empty)
+ PyObject *empty = unicode_get_empty(); // Borrowed reference
+ if (left == empty) {
return PyUnicode_FromObject(right);
- if (right == unicode_empty)
+ }
+ if (right == empty) {
return PyUnicode_FromObject(left);
+ }
left_len = PyUnicode_GET_LENGTH(left);
right_len = PyUnicode_GET_LENGTH(right);
@@ -11551,14 +11586,16 @@
goto error;
/* Shortcuts */
- if (left == unicode_empty) {
+ PyObject *empty = unicode_get_empty(); // Borrowed reference
+ if (left == empty) {
Py_DECREF(left);
Py_INCREF(right);
*p_left = right;
return;
}
- if (right == unicode_empty)
+ if (right == empty) {
return;
+ }
left_len = PyUnicode_GET_LENGTH(left);
right_len = PyUnicode_GET_LENGTH(right);
@@ -13255,12 +13292,12 @@
len1 = PyUnicode_GET_LENGTH(str_obj);
len2 = PyUnicode_GET_LENGTH(sep_obj);
if (kind1 < kind2 || len1 < len2) {
- _Py_INCREF_UNICODE_EMPTY();
- if (!unicode_empty)
+ PyObject *empty = unicode_get_empty(); // Borrowed reference
+ if (!empty) {
out = NULL;
+ }
else {
- out = PyTuple_Pack(3, str_obj, unicode_empty, unicode_empty);
- Py_DECREF(unicode_empty);
+ out = PyTuple_Pack(3, str_obj, empty, empty);
}
return out;
}
@@ -13313,12 +13350,12 @@
len1 = PyUnicode_GET_LENGTH(str_obj);
len2 = PyUnicode_GET_LENGTH(sep_obj);
if (kind1 < kind2 || len1 < len2) {
- _Py_INCREF_UNICODE_EMPTY();
- if (!unicode_empty)
+ PyObject *empty = unicode_get_empty(); // Borrowed reference
+ if (!empty) {
out = NULL;
+ }
else {
- out = PyTuple_Pack(3, unicode_empty, unicode_empty, str_obj);
- Py_DECREF(unicode_empty);
+ out = PyTuple_Pack(3, empty, empty, str_obj);
}
return out;
}
@@ -15538,10 +15575,10 @@
/* Initialize the Unicode implementation */
PyStatus
-_PyUnicode_Init(void)
+_PyUnicode_Init(PyThreadState *tstate)
{
/* XXX - move this array to unicodectype.c ? */
- Py_UCS2 linebreak[] = {
+ const Py_UCS2 linebreak[] = {
0x000A, /* LINE FEED */
0x000D, /* CARRIAGE RETURN */
0x001C, /* FILE SEPARATOR */
@@ -15553,29 +15590,31 @@
};
/* Init the implementation */
- _Py_INCREF_UNICODE_EMPTY();
- if (!unicode_empty) {
- return _PyStatus_ERR("Can't create empty string");
+ PyObject *empty = unicode_new_empty();
+ if (!empty) {
+ return _PyStatus_NO_MEMORY();
}
- Py_DECREF(unicode_empty);
+ Py_DECREF(empty);
- if (PyType_Ready(&PyUnicode_Type) < 0) {
- return _PyStatus_ERR("Can't initialize unicode type");
- }
+ if (_Py_IsMainInterpreter(tstate)) {
+ /* initialize the linebreak bloom filter */
+ bloom_linebreak = make_bloom_mask(
+ PyUnicode_2BYTE_KIND, linebreak,
+ Py_ARRAY_LENGTH(linebreak));
- /* initialize the linebreak bloom filter */
- bloom_linebreak = make_bloom_mask(
- PyUnicode_2BYTE_KIND, linebreak,
- Py_ARRAY_LENGTH(linebreak));
+ if (PyType_Ready(&PyUnicode_Type) < 0) {
+ return _PyStatus_ERR("Can't initialize unicode type");
+ }
- if (PyType_Ready(&EncodingMapType) < 0) {
- return _PyStatus_ERR("Can't initialize encoding map type");
- }
- if (PyType_Ready(&PyFieldNameIter_Type) < 0) {
- return _PyStatus_ERR("Can't initialize field name iterator type");
- }
- if (PyType_Ready(&PyFormatterIter_Type) < 0) {
- return _PyStatus_ERR("Can't initialize formatter iter type");
+ if (PyType_Ready(&EncodingMapType) < 0) {
+ return _PyStatus_ERR("Can't initialize encoding map type");
+ }
+ if (PyType_Ready(&PyFieldNameIter_Type) < 0) {
+ return _PyStatus_ERR("Can't initialize field name iterator type");
+ }
+ if (PyType_Ready(&PyFormatterIter_Type) < 0) {
+ return _PyStatus_ERR("Can't initialize formatter iter type");
+ }
}
return _PyStatus_OK();
}
@@ -16205,7 +16244,10 @@
void
_PyUnicode_Fini(PyThreadState *tstate)
{
- if (_Py_IsMainInterpreter(tstate)) {
+ struct _Py_unicode_state *state = &tstate->interp->unicode;
+
+ int is_main_interp = _Py_IsMainInterpreter(tstate);
+ if (is_main_interp) {
#if defined(WITH_VALGRIND) || defined(__INSURE__)
/* Insure++ is a memory analysis tool that aids in discovering
* memory leaks and other memory problems. On Python exit, the
@@ -16218,9 +16260,11 @@
*/
unicode_release_interned();
#endif /* __INSURE__ */
+ }
- Py_CLEAR(unicode_empty);
+ Py_CLEAR(state->empty);
+ if (is_main_interp) {
#ifdef LATIN1_SINGLETONS
for (Py_ssize_t i = 0; i < 256; i++) {
Py_CLEAR(unicode_latin1[i]);