gh-120974: Use common freelist code in asyncio (#122132)

This refactors asyncio to use the common freelist helper functions and
macros. As a side effect, the freelist for _asyncio.Future is now
re-enabled in the free-threaded build.

Author: colesbury

Include/internal/pycore_freelist_state.h

@@ -20,6 +20,7 @@ extern "C" {
 #  define Py_contexts_MAXFREELIST 255
 #  define Py_async_gens_MAXFREELIST 80
 #  define Py_async_gen_asends_MAXFREELIST 80
+#  define Py_futureiters_MAXFREELIST 255
 #  define Py_object_stack_chunks_MAXFREELIST 4
 #else
 #  define PyTuple_MAXSAVESIZE 0
@@ -47,6 +48,7 @@ struct _Py_freelists {
     struct _Py_freelist contexts;
     struct _Py_freelist async_gens;
     struct _Py_freelist async_gen_asends;
+    struct _Py_freelist futureiters;
     struct _Py_freelist object_stack_chunks;
 #else
     char _unused;  // Empty structs are not allowed.

Modules/_asynciomodule.c

@@ -4,6 +4,7 @@
 
 #include "Python.h"
 #include "pycore_dict.h"          // _PyDict_GetItem_KnownHash()
+#include "pycore_freelist.h"      // _Py_FREELIST_POP()
 #include "pycore_modsupport.h"    // _PyArg_CheckPositional()
 #include "pycore_moduleobject.h"  // _PyModule_GetState()
 #include "pycore_object.h"        // _Py_SetImmortalUntracked
@@ -75,8 +76,6 @@ typedef struct {
 #define Future_Check(state, obj) PyObject_TypeCheck(obj, state->FutureType)
 #define Task_Check(state, obj) PyObject_TypeCheck(obj, state->TaskType)
 
-#define FI_FREELIST_MAXLEN 255
-
 #ifdef Py_GIL_DISABLED
 #   define ASYNCIO_STATE_LOCK(state) PyMutex_Lock(&state->mutex)
 #   define ASYNCIO_STATE_UNLOCK(state) PyMutex_Unlock(&state->mutex)
@@ -138,11 +137,6 @@ typedef struct {
     /* Counter for autogenerated Task names */
     uint64_t task_name_counter;
 
-#ifndef Py_GIL_DISABLED
-    futureiterobject *fi_freelist;
-    Py_ssize_t fi_freelist_len;
-#endif
-
     /* Linked-list of all tasks which are instances of asyncio.Task or subclasses
        of it. Third party tasks implementations which don't inherit from
        asyncio.Task are tracked separately using the 'non_asyncio_tasks' WeakSet.
@@ -1584,24 +1578,7 @@ FutureIter_dealloc(futureiterobject *it)
     PyObject_GC_UnTrack(it);
     tp->tp_clear((PyObject *)it);
 
-#ifndef Py_GIL_DISABLED
-    // GH-115874: We can't use PyType_GetModuleByDef here as the type might have
-    // already been cleared, which is also why we must check if ht_module != NULL.
-    PyObject *module = ((PyHeapTypeObject*)tp)->ht_module;
-    asyncio_state *state = NULL;
-    if (module && _PyModule_GetDef(module) == &_asynciomodule) {
-        state = get_asyncio_state(module);
-    }
-
-    // TODO GH-121621: This should be moved to thread state as well.
-    if (state && state->fi_freelist_len < FI_FREELIST_MAXLEN) {
-        state->fi_freelist_len++;
-        it->future = (FutureObj*) state->fi_freelist;
-        state->fi_freelist = it;
-    }
-    else
-#endif
-    {
+    if (!_Py_FREELIST_PUSH(futureiters, it, Py_futureiters_MAXFREELIST)) {
         PyObject_GC_Del(it);
         Py_DECREF(tp);
     }
@@ -1805,17 +1782,8 @@ future_new_iter(PyObject *fut)
     asyncio_state *state = get_asyncio_state_by_def((PyObject *)fut);
     ENSURE_FUTURE_ALIVE(state, fut)
 
-#ifndef Py_GIL_DISABLED
-    if (state->fi_freelist_len) {
-        state->fi_freelist_len--;
-        it = state->fi_freelist;
-        state->fi_freelist = (futureiterobject*) it->future;
-        it->future = NULL;
-        _Py_NewReference((PyObject*) it);
-    }
-    else
-#endif
-    {
+    it = _Py_FREELIST_POP(futureiterobject, futureiters);
+    if (it == NULL) {
         it = PyObject_GC_New(futureiterobject, state->FutureIterType);
         if (it == NULL) {
             return NULL;
@@ -3678,27 +3646,6 @@ _asyncio_all_tasks_impl(PyObject *module, PyObject *loop)
     return tasks;
 }
 
-static void
-module_free_freelists(asyncio_state *state)
-{
-#ifndef Py_GIL_DISABLED
-    PyObject *next;
-    PyObject *current;
-
-    next = (PyObject*) state->fi_freelist;
-    while (next != NULL) {
-        assert(state->fi_freelist_len > 0);
-        state->fi_freelist_len--;
-
-        current = next;
-        next = (PyObject*) ((futureiterobject*) current)->future;
-        PyObject_GC_Del(current);
-    }
-    assert(state->fi_freelist_len == 0);
-    state->fi_freelist = NULL;
-#endif
-}
-
 static int
 module_traverse(PyObject *mod, visitproc visit, void *arg)
 {
@@ -3727,16 +3674,6 @@ module_traverse(PyObject *mod, visitproc visit, void *arg)
 
     Py_VISIT(state->context_kwname);
 
-#ifndef Py_GIL_DISABLED
-    // Visit freelist.
-    PyObject *next = (PyObject*) state->fi_freelist;
-    while (next != NULL) {
-        PyObject *current = next;
-        Py_VISIT(current);
-        next = (PyObject*) ((futureiterobject*) current)->future;
-    }
-#endif
-
     return 0;
 }
 
@@ -3768,8 +3705,6 @@ module_clear(PyObject *mod)
 
     Py_CLEAR(state->context_kwname);
 
-    module_free_freelists(state);
-
     return 0;
 }
 

Objects/object.c

@@ -829,7 +829,9 @@ static void
 free_object(void *obj)
 {
     PyObject *op = (PyObject *)obj;
-    Py_TYPE(op)->tp_free(op);
+    PyTypeObject *tp = Py_TYPE(op);
+    tp->tp_free(op);
+    Py_DECREF(tp);
 }
 
 #endif
@@ -851,6 +853,7 @@ _PyObject_ClearFreeLists(struct _Py_freelists *freelists, int is_finalization)
     clear_freelist(&freelists->contexts, is_finalization, free_object);
     clear_freelist(&freelists->async_gens, is_finalization, free_object);
     clear_freelist(&freelists->async_gen_asends, is_finalization, free_object);
+    clear_freelist(&freelists->futureiters, is_finalization, free_object);
     if (is_finalization) {
         // Only clear object stack chunks during finalization. We use object
         // stacks during GC, so emptying the free-list is counterproductive.