bpo-39465: Fix _PyUnicode_FromId() for subinterpreters (GH-20058)
Make _PyUnicode_FromId() function compatible with subinterpreters.
Each interpreter now has an array of identifier objects (interned
strings decoded from UTF-8).
* Add PyInterpreterState.unicode.identifiers: array of identifiers
objects.
* Add _PyRuntimeState.unicode_ids used to allocate unique indexes
to _Py_Identifier.
* Rewrite the _Py_Identifier structure.
Microbenchmark on _PyUnicode_FromId(&PyId_a) with _Py_IDENTIFIER(a):
[ref] 2.42 ns +- 0.00 ns -> [atomic] 3.39 ns +- 0.00 ns: 1.40x slower
This change adds 1 ns per _PyUnicode_FromId() call in average.
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index 4093555..3238d1e 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -41,6 +41,7 @@ OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
#define PY_SSIZE_T_CLEAN
#include "Python.h"
#include "pycore_abstract.h" // _PyIndex_Check()
+#include "pycore_atomic_funcs.h" // _Py_atomic_size_get()
#include "pycore_bytes_methods.h" // _Py_bytes_lower()
#include "pycore_format.h" // F_LJUST
#include "pycore_initconfig.h" // _PyStatus_OK()
@@ -302,9 +303,6 @@ unicode_decode_utf8(const char *s, Py_ssize_t size,
_Py_error_handler error_handler, const char *errors,
Py_ssize_t *consumed);
-/* List of static strings. */
-static _Py_Identifier *static_strings = NULL;
-
/* Fast detection of the most frequent whitespace characters */
const unsigned char _Py_ascii_whitespace[] = {
0, 0, 0, 0, 0, 0, 0, 0,
@@ -2312,42 +2310,85 @@ PyUnicode_FromString(const char *u)
return PyUnicode_DecodeUTF8Stateful(u, (Py_ssize_t)size, NULL, NULL);
}
+
PyObject *
_PyUnicode_FromId(_Py_Identifier *id)
{
- if (id->object) {
- return id->object;
+ PyInterpreterState *interp = _PyInterpreterState_GET();
+ struct _Py_unicode_ids *ids = &interp->unicode.ids;
+
+ int index = _Py_atomic_size_get(&id->index);
+ if (index < 0) {
+ struct _Py_unicode_runtime_ids *rt_ids = &interp->runtime->unicode_ids;
+
+ PyThread_acquire_lock(rt_ids->lock, WAIT_LOCK);
+ // Check again to detect concurrent access. Another thread can have
+ // initialized the index while this thread waited for the lock.
+ index = _Py_atomic_size_get(&id->index);
+ if (index < 0) {
+ assert(rt_ids->next_index < PY_SSIZE_T_MAX);
+ index = rt_ids->next_index;
+ rt_ids->next_index++;
+ _Py_atomic_size_set(&id->index, index);
+ }
+ PyThread_release_lock(rt_ids->lock);
}
+ assert(index >= 0);
PyObject *obj;
- obj = PyUnicode_DecodeUTF8Stateful(id->string,
- strlen(id->string),
+ if (index < ids->size) {
+ obj = ids->array[index];
+ if (obj) {
+ // Return a borrowed reference
+ return obj;
+ }
+ }
+
+ obj = PyUnicode_DecodeUTF8Stateful(id->string, strlen(id->string),
NULL, NULL);
if (!obj) {
return NULL;
}
PyUnicode_InternInPlace(&obj);
- assert(!id->next);
- id->object = obj;
- id->next = static_strings;
- static_strings = id;
- return id->object;
+ if (index >= ids->size) {
+ // Overallocate to reduce the number of realloc
+ Py_ssize_t new_size = Py_MAX(index * 2, 16);
+ Py_ssize_t item_size = sizeof(ids->array[0]);
+ PyObject **new_array = PyMem_Realloc(ids->array, new_size * item_size);
+ if (new_array == NULL) {
+ PyErr_NoMemory();
+ return NULL;
+ }
+ memset(&new_array[ids->size], 0, (new_size - ids->size) * item_size);
+ ids->array = new_array;
+ ids->size = new_size;
+ }
+
+ // The array stores a strong reference
+ ids->array[index] = obj;
+
+ // Return a borrowed reference
+ return obj;
}
+
static void
-unicode_clear_static_strings(void)
+unicode_clear_identifiers(PyThreadState *tstate)
{
- _Py_Identifier *tmp, *s = static_strings;
- while (s) {
- Py_CLEAR(s->object);
- tmp = s->next;
- s->next = NULL;
- s = tmp;
+ PyInterpreterState *interp = _PyInterpreterState_GET();
+ struct _Py_unicode_ids *ids = &interp->unicode.ids;
+ for (Py_ssize_t i=0; i < ids->size; i++) {
+ Py_XDECREF(ids->array[i]);
}
- static_strings = NULL;
+ ids->size = 0;
+ PyMem_Free(ids->array);
+ ids->array = NULL;
+ // Don't reset _PyRuntime next_index: _Py_Identifier.id remains valid
+ // after Py_Finalize().
}
+
/* Internal function, doesn't check maximum character */
PyObject*
@@ -16238,9 +16279,7 @@ _PyUnicode_Fini(PyThreadState *tstate)
Py_CLEAR(state->latin1[i]);
}
- if (_Py_IsMainInterpreter(tstate)) {
- unicode_clear_static_strings();
- }
+ unicode_clear_identifiers(tstate);
_PyUnicode_FiniEncodings(&tstate->interp->unicode.fs_codec);
}