bpo-39465: Fix _PyUnicode_FromId() for subinterpreters

Include/cpython/object.h

@@ -35,12 +35,13 @@ PyAPI_FUNC(Py_ssize_t) _Py_GetRefTotal(void);
  _PyObject_{Get,Set,Has}AttrId are __getattr__ versions using _Py_Identifier*.
 */
 typedef struct _Py_Identifier{
- struct _Py_Identifier *next;
  const char* string;
- PyObject *object;
+ // Index in PyInterpreterState.unicode.ids.array. It is process-wide
+ // unique and must be initialized to -1.
+ Py_ssize_t index;
 } _Py_Identifier;
 
-#define _Py_static_string_init(value){.next = NULL, .string = value, .object = NULL }
+#define _Py_static_string_init(value){.string = value, .index = -1 }
 #define _Py_static_string(varname, value) static _Py_Identifier varname = _Py_static_string_init(value)
 #define _Py_IDENTIFIER(varname) _Py_static_string(PyId_##varname, #varname)
 

Include/internal/pycore_interp.h

@@ -64,13 +64,20 @@ struct _Py_bytes_state{
  PyBytesObject *characters[256];
 };
 
+struct _Py_unicode_ids{
+ Py_ssize_t size;
+ PyObject **array;
+};
+
 struct _Py_unicode_state{
  // The empty Unicode object is a singleton to improve performance.
  PyObject *empty_string;
  /* Single character Unicode strings in the Latin-1 range are being
  shared as well. */
  PyObject *latin1[256];
  struct _Py_unicode_fs_codec fs_codec;
+ // Unicode identifiers (_Py_Identifier): see _PyUnicode_FromId()
+ struct _Py_unicode_ids ids;
 };
 
 struct _Py_float_state{

Include/internal/pycore_runtime.h

@@ -49,6 +49,11 @@ typedef struct _Py_AuditHookEntry{
  void *userData;
 } _Py_AuditHookEntry;
 
+struct _Py_unicode_runtime_ids{
+ PyThread_type_lock lock;
+ Py_ssize_t next_index;
+};
+
 /* Full Python runtime state */
 
 typedef struct pyruntimestate{
@@ -106,6 +111,8 @@ typedef struct pyruntimestate{
  void *open_code_userdata;
  _Py_AuditHookEntry *audit_hook_head;
 
+ struct _Py_unicode_runtime_ids unicode_ids;
+
  // XXX Consolidate globals found via the check-c-globals script.
 } _PyRuntimeState;
 

Misc/NEWS.d/next/Core and Builtins/2020-05-13-18-50-27.bpo-39465.j7nl6A.rst

@@ -0,0 +1,3 @@
+Make :c:func:`_PyUnicode_FromId` function compatible with subinterpreters.
+Each interpreter now has an array of identifier objects (interned strings
+decoded from UTF-8). Patch by Victor Stinner.

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);
 }

Python/pystate.c

@@ -73,18 +73,24 @@ _PyRuntimeState_Init_impl(_PyRuntimeState *runtime)
 
  runtime->interpreters.mutex = PyThread_allocate_lock();
  if (runtime->interpreters.mutex == NULL){
- return _PyStatus_ERR("Can't initialize threads for interpreter");
+ return _PyStatus_NO_MEMORY();
  }
  runtime->interpreters.next_id = -1;
 
  runtime->xidregistry.mutex = PyThread_allocate_lock();
  if (runtime->xidregistry.mutex == NULL){
- return _PyStatus_ERR("Can't initialize threads for cross-interpreter data registry");
+ return _PyStatus_NO_MEMORY();
  }
 
  // Set it to the ID of the main thread of the main interpreter.
  runtime->main_thread = PyThread_get_thread_ident();
 
+ runtime->unicode_ids.lock = PyThread_allocate_lock();
+ if (runtime->unicode_ids.lock == NULL){
+ return _PyStatus_NO_MEMORY();
+ }
+ runtime->unicode_ids.next_index = 0;
+
  return _PyStatus_OK();
 }
 
@@ -108,17 +114,17 @@ _PyRuntimeState_Fini(_PyRuntimeState *runtime)
  /* Force the allocator used by _PyRuntimeState_Init(). */
  PyMemAllocatorEx old_alloc;
  _PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
-
- if (runtime->interpreters.mutex != NULL){
- PyThread_free_lock(runtime->interpreters.mutex);
-runtime->interpreters.mutex = NULL;
+#define FREE_LOCK(LOCK) \
+ if (LOCK != NULL){ \
+ PyThread_free_lock(LOCK); \
+LOCK = NULL; \
  }
 
- if (runtime->xidregistry.mutex != NULL){
- PyThread_free_lock(runtime->xidregistry.mutex);
- runtime->xidregistry.mutex = NULL;
- }
+ FREE_LOCK(runtime->interpreters.mutex);
+ FREE_LOCK(runtime->xidregistry.mutex);
+ FREE_LOCK(runtime->unicode_ids.lock);
 
+#undef FREE_LOCK
  PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
 }
 
@@ -139,12 +145,14 @@ _PyRuntimeState_ReInitThreads(_PyRuntimeState *runtime)
  int reinit_interp = _PyThread_at_fork_reinit(&runtime->interpreters.mutex);
  int reinit_main_id = _PyThread_at_fork_reinit(&runtime->interpreters.main->id_mutex);
  int reinit_xidregistry = _PyThread_at_fork_reinit(&runtime->xidregistry.mutex);
+ int reinit_unicode_ids = _PyThread_at_fork_reinit(&runtime->unicode_ids.lock);
 
  PyMem_SetAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
 
  if (reinit_interp < 0
  || reinit_main_id < 0
- || reinit_xidregistry < 0)
+ || reinit_xidregistry < 0
+ || reinit_unicode_ids < 0)
 {
  return _PyStatus_ERR("Failed to reinitialize runtime locks");