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bpo-40521: Make Unicode latin1 singletons per interpreter #21101

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Jun 24, 2020
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bpo-40521: Make Unicode latin1 singletons per interpreter #21101

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3 changes: 3 additions & 0 deletions Include/internal/pycore_interp.h
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Original file line number Diff line number Diff line change
Expand Up @@ -73,6 +73,9 @@ struct _Py_bytes_state {
struct _Py_unicode_state {
// The empty Unicode object is a singleton to improve performance.
PyObject *empty;
/* Single character Unicode strings in the Latin-1 range are being
shared as well. */
PyObject *latin1[256];
struct _Py_unicode_fs_codec fs_codec;
};

Expand Down
2 changes: 1 addition & 1 deletion Misc/NEWS.d/next/Core and Builtins/2020-05-20-01-17-34.bpo-40521.wvAehI.rst
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Expand Up @@ -3,7 +3,7 @@ Each interpreter now its has own free lists, singletons and caches:
* Free lists: float, tuple, list, dict, frame, context,
asynchronous generator, MemoryError.
* Singletons: empty tuple, empty bytes string, empty Unicode string,
single byte character.
single byte character, single Unicode (latin1) character.
* Slice cache.

They are no longer shared by all interpreters.
74 changes: 32 additions & 42 deletions Objects/unicodeobject.c
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Expand Up @@ -303,17 +303,6 @@ unicode_decode_utf8(const char *s, Py_ssize_t size,
/* List of static strings. */
static _Py_Identifier *static_strings = NULL;

/* bpo-40521: Latin1 singletons are shared by all interpreters. */
#ifndef EXPERIMENTAL_ISOLATED_SUBINTERPRETERS
# define LATIN1_SINGLETONS
#endif

#ifdef LATIN1_SINGLETONS
/* Single character Unicode strings in the Latin-1 range are being
shared as well. */
static PyObject *unicode_latin1[256] = {NULL};
#endif

/* Fast detection of the most frequent whitespace characters */
const unsigned char _Py_ascii_whitespace[] = {
0, 0, 0, 0, 0, 0, 0, 0,
Expand Down Expand Up @@ -657,9 +646,8 @@ unicode_result_wchar(PyObject *unicode)
if (len == 1) {
wchar_t ch = _PyUnicode_WSTR(unicode)[0];
if ((Py_UCS4)ch < 256) {
PyObject *latin1_char = get_latin1_char((unsigned char)ch);
Py_DECREF(unicode);
return latin1_char;
return get_latin1_char((unsigned char)ch);
}
}

Expand Down Expand Up @@ -692,13 +680,13 @@ unicode_result_ready(PyObject *unicode)
return empty;
}

#ifdef LATIN1_SINGLETONS
if (length == 1) {
const void *data = PyUnicode_DATA(unicode);
int kind = PyUnicode_KIND(unicode);
Py_UCS4 ch = PyUnicode_READ(kind, data, 0);
if (ch < 256) {
PyObject *latin1_char = unicode_latin1[ch];
if (kind == PyUnicode_1BYTE_KIND) {
Py_UCS1 *data = PyUnicode_1BYTE_DATA(unicode);
Py_UCS1 ch = data[0];
struct _Py_unicode_state *state = get_unicode_state();
PyObject *latin1_char = state->latin1[ch];
if (latin1_char != NULL) {
if (unicode != latin1_char) {
Py_INCREF(latin1_char);
Expand All @@ -709,12 +697,14 @@ unicode_result_ready(PyObject *unicode)
else {
assert(_PyUnicode_CheckConsistency(unicode, 1));
Py_INCREF(unicode);
unicode_latin1[ch] = unicode;
state->latin1[ch] = unicode;
return unicode;
}
}
else {
assert(PyUnicode_READ_CHAR(unicode, 0) >= 256);
}
}
#endif

assert(_PyUnicode_CheckConsistency(unicode, 1));
return unicode;
Expand Down Expand Up @@ -1981,18 +1971,18 @@ unicode_dealloc(PyObject *unicode)
static int
unicode_is_singleton(PyObject *unicode)
{
if (unicode == unicode_get_empty()) {
struct _Py_unicode_state *state = get_unicode_state();
if (unicode == state->empty) {
return 1;
}
#ifdef LATIN1_SINGLETONS
PyASCIIObject *ascii = (PyASCIIObject *)unicode;
if (ascii->state.kind != PyUnicode_WCHAR_KIND && ascii->length == 1)
{
Py_UCS4 ch = PyUnicode_READ_CHAR(unicode, 0);
if (ch < 256 && unicode_latin1[ch] == unicode)
if (ch < 256 && state->latin1[ch] == unicode) {
return 1;
}
}
#endif
return 0;
}
#endif
Expand Down Expand Up @@ -2130,17 +2120,15 @@ unicode_write_cstr(PyObject *unicode, Py_ssize_t index,
}

static PyObject*
get_latin1_char(unsigned char ch)
get_latin1_char(Py_UCS1 ch)
{
PyObject *unicode;
struct _Py_unicode_state *state = get_unicode_state();

#ifdef LATIN1_SINGLETONS
unicode = unicode_latin1[ch];
PyObject *unicode = state->latin1[ch];
if (unicode) {
Py_INCREF(unicode);
return unicode;
}
#endif

unicode = PyUnicode_New(1, ch);
if (!unicode) {
Expand All @@ -2150,10 +2138,8 @@ get_latin1_char(unsigned char ch)
PyUnicode_1BYTE_DATA(unicode)[0] = ch;
assert(_PyUnicode_CheckConsistency(unicode, 1));

#ifdef LATIN1_SINGLETONS
Py_INCREF(unicode);
unicode_latin1[ch] = unicode;
#endif
state->latin1[ch] = unicode;
return unicode;
}

Expand All @@ -2164,8 +2150,9 @@ unicode_char(Py_UCS4 ch)

assert(ch <= MAX_UNICODE);

if (ch < 256)
if (ch < 256) {
return get_latin1_char(ch);
}

unicode = PyUnicode_New(1, ch);
if (unicode == NULL)
Expand Down Expand Up @@ -2367,11 +2354,13 @@ _PyUnicode_FromUCS1(const Py_UCS1* u, Py_ssize_t size)
PyObject *res;
unsigned char max_char;

if (size == 0)
if (size == 0) {
_Py_RETURN_UNICODE_EMPTY();
}
assert(size > 0);
if (size == 1)
if (size == 1) {
return get_latin1_char(u[0]);
}

max_char = ucs1lib_find_max_char(u, u + size);
res = PyUnicode_New(size, max_char);
Expand Down Expand Up @@ -5008,8 +4997,9 @@ unicode_decode_utf8(const char *s, Py_ssize_t size,

/* ASCII is equivalent to the first 128 ordinals in Unicode. */
if (size == 1 && (unsigned char)s[0] < 128) {
if (consumed)
if (consumed) {
*consumed = 1;
}
return get_latin1_char((unsigned char)s[0]);
}

Expand Down Expand Up @@ -7176,8 +7166,9 @@ PyUnicode_DecodeASCII(const char *s,
_Py_RETURN_UNICODE_EMPTY();

/* ASCII is equivalent to the first 128 ordinals in Unicode. */
if (size == 1 && (unsigned char)s[0] < 128)
if (size == 1 && (unsigned char)s[0] < 128) {
return get_latin1_char((unsigned char)s[0]);
}

// Shortcut for simple case
PyObject *u = PyUnicode_New(size, 127);
Expand Down Expand Up @@ -16234,12 +16225,11 @@ _PyUnicode_Fini(PyThreadState *tstate)

Py_CLEAR(state->empty);

for (Py_ssize_t i = 0; i < 256; i++) {
Py_CLEAR(state->latin1[i]);
}

if (is_main_interp) {
#ifdef LATIN1_SINGLETONS
for (Py_ssize_t i = 0; i < 256; i++) {
Py_CLEAR(unicode_latin1[i]);
}
#endif
unicode_clear_static_strings();
}

Expand Down