Backout c89febab4648 following private feedback by Guido.

(Issue #17807: Generators can now be finalized even when they are part of a reference cycle)

Include/frameobject.h

@@ -36,8 +36,6 @@ typedef struct _frame {
            non-generator frames. See the save_exc_state and swap_exc_state
            functions in ceval.c for details of their use. */
     PyObject *f_exc_type, *f_exc_value, *f_exc_traceback;
-    /* Borrowed referenced to a generator, or NULL */
-    PyObject *f_gen;
 
     PyThreadState *f_tstate;
     int f_lasti;                /* Last instruction if called */
@@ -86,13 +84,6 @@ PyAPI_FUNC(void) _PyFrame_DebugMallocStats(FILE *out);
 /* Return the line of code the frame is currently executing. */
 PyAPI_FUNC(int) PyFrame_GetLineNumber(PyFrameObject *);
 
-/* Generator support */
-PyAPI_FUNC(PyObject *) _PyFrame_YieldingFrom(PyFrameObject *);
-PyAPI_FUNC(PyObject *) _PyFrame_GeneratorSend(PyFrameObject *, PyObject *, int exc);
-PyAPI_FUNC(PyObject *) _PyFrame_Finalize(PyFrameObject *);
-PyAPI_FUNC(int) _PyFrame_CloseIterator(PyObject *);
-
-
 #ifdef __cplusplus
 }
 #endif

Include/genobject.h

@@ -33,7 +33,6 @@ PyAPI_DATA(PyTypeObject) PyGen_Type;
 #define PyGen_CheckExact(op) (Py_TYPE(op) == &PyGen_Type)
 
 PyAPI_FUNC(PyObject *) PyGen_New(struct _frame *);
-/* Deprecated, kept for backwards compatibility. */
 PyAPI_FUNC(int) PyGen_NeedsFinalizing(PyGenObject *);
 PyAPI_FUNC(int) _PyGen_FetchStopIterationValue(PyObject **);
 PyObject *_PyGen_Send(PyGenObject *, PyObject *);

Lib/test/test_generators.py

@@ -1,55 +1,3 @@
-import gc
-import sys
-import unittest
-import weakref
-
-from test import support
-
-
-class FinalizationTest(unittest.TestCase):
-
-    def test_frame_resurrect(self):
-        # A generator frame can be resurrected by a generator's finalization.
-        def gen():
-            nonlocal frame
-            try:
-                yield
-            finally:
-                frame = sys._getframe()
-
-        g = gen()
-        wr = weakref.ref(g)
-        next(g)
-        del g
-        support.gc_collect()
-        self.assertIs(wr(), None)
-        self.assertTrue(frame)
-        del frame
-        support.gc_collect()
-
-    def test_refcycle(self):
-        # A generator caught in a refcycle gets finalized anyway.
-        old_garbage = gc.garbage[:]
-        finalized = False
-        def gen():
-            nonlocal finalized
-            try:
-                g = yield
-                yield 1
-            finally:
-                finalized = True
-
-        g = gen()
-        next(g)
-        g.send(g)
-        self.assertGreater(sys.getrefcount(g), 2)
-        self.assertFalse(finalized)
-        del g
-        support.gc_collect()
-        self.assertTrue(finalized)
-        self.assertEqual(gc.garbage, old_garbage)
-
-
 tutorial_tests = """
 Let's try a simple generator:
 
@@ -1932,7 +1880,6 @@ __test__ = {"tut":      tutorial_tests,
 # so this works as expected in both ways of running regrtest.
 def test_main(verbose=None):
     from test import support, test_generators
-    support.run_unittest(__name__)
     support.run_doctest(test_generators, verbose)
 
 # This part isn't needed for regrtest, but for running the test directly.

Lib/test/test_sys.py

@@ -764,7 +764,7 @@ class SizeofTest(unittest.TestCase):
         nfrees = len(x.f_code.co_freevars)
         extras = x.f_code.co_stacksize + x.f_code.co_nlocals +\
                   ncells + nfrees - 1
-        check(x, vsize('13P3i' + CO_MAXBLOCKS*'3i' + 'P' + extras*'P'))
+        check(x, vsize('12P3i' + CO_MAXBLOCKS*'3i' + 'P' + extras*'P'))
         # function
         def func(): pass
         check(func, size('12P'))

Misc/NEWS

@@ -15,9 +15,6 @@ Core and Builtins
 - Issue #17927: Frame objects kept arguments alive if they had been
   copied into a cell, even if the cell was cleared.
 
-- Issue #17807: Generators can now be finalized even when they are part of
-  a reference cycle.
-
 - Issue #1545463: At shutdown, defer finalization of codec modules so
   that stderr remains usable.
 

Modules/gcmodule.c

@@ -524,7 +524,10 @@ untrack_dicts(PyGC_Head *head)
 static int
 has_finalizer(PyObject *op)
 {
-    return op->ob_type->tp_del != NULL;
+    if (PyGen_CheckExact(op))
+        return PyGen_NeedsFinalizing((PyGenObject *)op);
+    else
+        return op->ob_type->tp_del != NULL;
 }
 
 /* Move the objects in unreachable with __del__ methods into `finalizers`.

Objects/frameobject.c

@@ -31,195 +31,6 @@ frame_getlocals(PyFrameObject *f, void *closure)
     return f->f_locals;
 }
 
-/*
- * Generator support.
- */
-
-PyObject *
-_PyFrame_YieldingFrom(PyFrameObject *f)
-{
-    PyObject *yf = NULL;
-
-    if (f && f->f_stacktop) {
-        PyObject *bytecode = f->f_code->co_code;
-        unsigned char *code = (unsigned char *)PyBytes_AS_STRING(bytecode);
-
-        if (code[f->f_lasti + 1] != YIELD_FROM)
-            return NULL;
-        yf = f->f_stacktop[-1];
-        Py_INCREF(yf);
-    }
-    return yf;
-}
-
-PyObject *
-_PyFrame_GeneratorSend(PyFrameObject *f, PyObject *arg, int exc)
-{
-    PyThreadState *tstate = PyThreadState_GET();
-    PyObject *result;
-    PyGenObject *gen = (PyGenObject *) f->f_gen;
-
-    assert(gen == NULL || PyGen_CheckExact(gen));
-    if (gen && gen->gi_running) {
-        PyErr_SetString(PyExc_ValueError,
-                        "generator already executing");
-        return NULL;
-    }
-    if (f->f_stacktop == NULL) {
-        /* Only set exception if send() called, not throw() or next() */
-        if (arg && !exc)
-            PyErr_SetNone(PyExc_StopIteration);
-        return NULL;
-    }
-
-    if (f->f_lasti == -1) {
-        if (arg && arg != Py_None) {
-            PyErr_SetString(PyExc_TypeError,
-                            "can't send non-None value to a "
-                            "just-started generator");
-            return NULL;
-        }
-    } else {
-        /* Push arg onto the frame's value stack */
-        result = arg ? arg : Py_None;
-        Py_INCREF(result);
-        *(f->f_stacktop++) = result;
-    }
-
-    /* Generators always return to their most recent caller, not
-     * necessarily their creator. */
-    Py_XINCREF(tstate->frame);
-    assert(f->f_back == NULL);
-    f->f_back = tstate->frame;
-
-    if (gen) {
-        Py_INCREF(gen);
-        gen->gi_running = 1;
-    }
-    result = PyEval_EvalFrameEx(f, exc);
-    if (gen) {
-        gen->gi_running = 0;
-        /* In case running the frame has lost all external references
-         * to gen, we must be careful not to hold on an invalid object. */
-        if (Py_REFCNT(gen) == 1)
-            Py_CLEAR(gen);
-        else
-            Py_DECREF(gen);
-    }
-
-    /* Don't keep the reference to f_back any longer than necessary.  It
-     * may keep a chain of frames alive or it could create a reference
-     * cycle. */
-    assert(f->f_back == tstate->frame);
-    Py_CLEAR(f->f_back);
-
-    /* If the generator just returned (as opposed to yielding), signal
-     * that the generator is exhausted. */
-    if (result && f->f_stacktop == NULL) {
-        if (result == Py_None) {
-            /* Delay exception instantiation if we can */
-            PyErr_SetNone(PyExc_StopIteration);
-        } else {
-            PyObject *e = PyObject_CallFunctionObjArgs(
-                               PyExc_StopIteration, result, NULL);
-            if (e != NULL) {
-                PyErr_SetObject(PyExc_StopIteration, e);
-                Py_DECREF(e);
-            }
-        }
-        Py_CLEAR(result);
-    }
-
-    if (f->f_stacktop == NULL) {
-        /* generator can't be rerun, so release the frame */
-        /* first clean reference cycle through stored exception traceback */
-        PyObject *t, *v, *tb;
-        t = f->f_exc_type;
-        v = f->f_exc_value;
-        tb = f->f_exc_traceback;
-        f->f_exc_type = NULL;
-        f->f_exc_value = NULL;
-        f->f_exc_traceback = NULL;
-        Py_XDECREF(t);
-        Py_XDECREF(v);
-        Py_XDECREF(tb);
-        if (gen) {
-            f->f_gen = NULL;
-            Py_CLEAR(gen->gi_frame);
-        }
-    }
-
-    return result;
-}
-
-int
-_PyFrame_CloseIterator(PyObject *yf)
-{
-    PyObject *retval = NULL;
-    _Py_IDENTIFIER(close);
-
-    if (PyGen_CheckExact(yf)) {
-        PyFrameObject *f = ((PyGenObject *) yf)->gi_frame;
-        assert(f != NULL);
-        retval = _PyFrame_Finalize(f);
-        if (retval == NULL)
-            return -1;
-    } else {
-        PyObject *meth = _PyObject_GetAttrId(yf, &PyId_close);
-        if (meth == NULL) {
-            if (!PyErr_ExceptionMatches(PyExc_AttributeError))
-                PyErr_WriteUnraisable(yf);
-            PyErr_Clear();
-        } else {
-            retval = PyObject_CallFunction(meth, "");
-            Py_DECREF(meth);
-            if (retval == NULL)
-                return -1;
-        }
-    }
-    Py_XDECREF(retval);
-    return 0;
-}
-
-PyObject *
-_PyFrame_Finalize(PyFrameObject *f)
-{
-    int err = 0;
-    PyObject *retval;
-    PyGenObject *gen = (PyGenObject *) f->f_gen;
-    PyObject *yf = _PyFrame_YieldingFrom(f);
-
-    assert(gen == NULL || PyGen_CheckExact(gen));
-    if (yf) {
-        if (gen)
-            gen->gi_running = 1;
-        err = _PyFrame_CloseIterator(yf);
-        if (gen)
-            gen->gi_running = 0;
-        Py_DECREF(yf);
-    }
-    if (err == 0)
-        PyErr_SetNone(PyExc_GeneratorExit);
-    retval = _PyFrame_GeneratorSend(f, Py_None, 1);
-    if (retval) {
-        Py_DECREF(retval);
-        PyErr_SetString(PyExc_RuntimeError,
-                        "generator ignored GeneratorExit");
-        return NULL;
-    }
-    if (PyErr_ExceptionMatches(PyExc_StopIteration)
-        || PyErr_ExceptionMatches(PyExc_GeneratorExit)) {
-        PyErr_Clear();          /* ignore these errors */
-        Py_INCREF(Py_None);
-        return Py_None;
-    }
-    return NULL;
-}
-
-/*
- * Line number support.
- */
-
 int
 PyFrame_GetLineNumber(PyFrameObject *f)
 {
@@ -608,44 +419,33 @@ static int numfree = 0;         /* number of frames currently in free_list */
 /* max value for numfree */
 #define PyFrame_MAXFREELIST 200
 
-static void
-frame_clear(PyFrameObject *f);
-
 static void
 frame_dealloc(PyFrameObject *f)
 {
+    PyObject **p, **valuestack;
     PyCodeObject *co;
 
-    Py_REFCNT(f)++;
-    frame_clear(f);
-    Py_REFCNT(f)--;
-    if (Py_REFCNT(f) > 0) {
-        /* Frame resurrected! */
-        Py_ssize_t refcnt = Py_REFCNT(f);
-        _Py_NewReference((PyObject *) f);
-        Py_REFCNT(f) = refcnt;
-        /* If Py_REF_DEBUG, _Py_NewReference bumped _Py_RefTotal, so
-         * we need to undo that. */
-        _Py_DEC_REFTOTAL;
-        /* If Py_TRACE_REFS, _Py_NewReference re-added self to the object
-         * chain, so no more to do there.
-         * If COUNT_ALLOCS, the original decref bumped tp_frees, and
-         * _Py_NewReference bumped tp_allocs:  both of those need to be
-         * undone.
-         */
-#ifdef COUNT_ALLOCS
-        --(Py_TYPE(self)->tp_frees);
-        --(Py_TYPE(self)->tp_allocs);
-#endif
-    }
-
     PyObject_GC_UnTrack(f);
     Py_TRASHCAN_SAFE_BEGIN(f)
+    /* Kill all local variables */
+    valuestack = f->f_valuestack;
+    for (p = f->f_localsplus; p < valuestack; p++)
+        Py_CLEAR(*p);
+
+    /* Free stack */
+    if (f->f_stacktop != NULL) {
+        for (p = valuestack; p < f->f_stacktop; p++)
+            Py_XDECREF(*p);
+    }
 
     Py_XDECREF(f->f_back);
     Py_DECREF(f->f_builtins);
     Py_DECREF(f->f_globals);
     Py_CLEAR(f->f_locals);
+    Py_CLEAR(f->f_trace);
+    Py_CLEAR(f->f_exc_type);
+    Py_CLEAR(f->f_exc_value);
+    Py_CLEAR(f->f_exc_traceback);
 
     co = f->f_code;
     if (co->co_zombieframe == NULL)
@@ -697,25 +497,12 @@ frame_clear(PyFrameObject *f)
 {
     PyObject **fastlocals, **p, **oldtop;
     Py_ssize_t i, slots;
-    PyObject *retval;
 
-    if (f->f_back == NULL) {
+    /* Before anything else, make sure that this frame is clearly marked
-        PyObject *t, *v, *tb;
+     * as being defunct!  Else, e.g., a generator reachable from this
-        PyErr_Fetch(&t, &v, &tb);
+     * frame may also point to this frame, believe itself to still be
-        /* Note that this can finalize a suspended generator frame even
+     * active, and try cleaning up this frame again.
-         * if the generator object was disposed of (i.e. if f_gen is NULL).
+     */
-         */
-        retval = _PyFrame_Finalize(f);
-        if (retval == NULL) {
-            if (PyErr_Occurred())
-                PyErr_WriteUnraisable((PyObject *) f);
-        }
-        else
-            Py_DECREF(retval);
-        PyErr_Restore(t, v, tb);
-    }
-
-    /* Make sure the frame is now clearly marked as being defunct */
     oldtop = f->f_stacktop;
     f->f_stacktop = NULL;
 
@@ -926,7 +713,6 @@ PyFrame_New(PyThreadState *tstate, PyCodeObject *code, PyObject *globals,
     f->f_lasti = -1;
     f->f_lineno = code->co_firstlineno;
     f->f_iblock = 0;
-    f->f_gen = NULL;
 
     _PyObject_GC_TRACK(f);
     return f;

Objects/genobject.c

@@ -19,50 +19,112 @@ static void
 gen_dealloc(PyGenObject *gen)
 {
     PyObject *self = (PyObject *) gen;
-    PyFrameObject *f = gen->gi_frame;
 
     _PyObject_GC_UNTRACK(gen);
 
     if (gen->gi_weakreflist != NULL)
         PyObject_ClearWeakRefs(self);
 
-    gen->gi_frame = NULL;
+    _PyObject_GC_TRACK(self);
-    if (f) {
+
-        /* Close the generator by finalizing the frame */
+    if (gen->gi_frame != NULL && gen->gi_frame->f_stacktop != NULL) {
-        PyObject *retval, *t, *v, *tb;
+        /* Generator is paused, so we need to close */
-        PyErr_Fetch(&t, &v, &tb);
+        Py_TYPE(gen)->tp_del(self);
-        f->f_gen = NULL;
+        if (self->ob_refcnt > 0)
-        retval = _PyFrame_Finalize(f);
+            return;                     /* resurrected.  :( */
-        if (retval)
-            Py_DECREF(retval);
-        else if (PyErr_Occurred())
-            PyErr_WriteUnraisable((PyObject *) gen);
-        Py_DECREF(f);
-        PyErr_Restore(t, v, tb);
     }
+
+    _PyObject_GC_UNTRACK(self);
+    Py_CLEAR(gen->gi_frame);
     Py_CLEAR(gen->gi_code);
     PyObject_GC_Del(gen);
 }
 
+
 static PyObject *
 gen_send_ex(PyGenObject *gen, PyObject *arg, int exc)
 {
+    PyThreadState *tstate = PyThreadState_GET();
     PyFrameObject *f = gen->gi_frame;
+    PyObject *result;
 
-    /* For compatibility, we check gi_running before f == NULL */
     if (gen->gi_running) {
         PyErr_SetString(PyExc_ValueError,
                         "generator already executing");
         return NULL;
     }
-    if (f == NULL) {
+    if (f == NULL || f->f_stacktop == NULL) {
-        /* Only set exception if send() called, not throw() or next() */
+        /* Only set exception if called from send() */
         if (arg && !exc)
             PyErr_SetNone(PyExc_StopIteration);
         return NULL;
     }
 
-    return _PyFrame_GeneratorSend(f, arg, exc);
+    if (f->f_lasti == -1) {
+        if (arg && arg != Py_None) {
+            PyErr_SetString(PyExc_TypeError,
+                            "can't send non-None value to a "
+                            "just-started generator");
+            return NULL;
+        }
+    } else {
+        /* Push arg onto the frame's value stack */
+        result = arg ? arg : Py_None;
+        Py_INCREF(result);
+        *(f->f_stacktop++) = result;
+    }
+
+    /* Generators always return to their most recent caller, not
+     * necessarily their creator. */
+    Py_XINCREF(tstate->frame);
+    assert(f->f_back == NULL);
+    f->f_back = tstate->frame;
+
+    gen->gi_running = 1;
+    result = PyEval_EvalFrameEx(f, exc);
+    gen->gi_running = 0;
+
+    /* Don't keep the reference to f_back any longer than necessary.  It
+     * may keep a chain of frames alive or it could create a reference
+     * cycle. */
+    assert(f->f_back == tstate->frame);
+    Py_CLEAR(f->f_back);
+
+    /* If the generator just returned (as opposed to yielding), signal
+     * that the generator is exhausted. */
+    if (result && f->f_stacktop == NULL) {
+        if (result == Py_None) {
+            /* Delay exception instantiation if we can */
+            PyErr_SetNone(PyExc_StopIteration);
+        } else {
+            PyObject *e = PyObject_CallFunctionObjArgs(
+                               PyExc_StopIteration, result, NULL);
+            if (e != NULL) {
+                PyErr_SetObject(PyExc_StopIteration, e);
+                Py_DECREF(e);
+            }
+        }
+        Py_CLEAR(result);
+    }
+
+    if (!result || f->f_stacktop == NULL) {
+        /* generator can't be rerun, so release the frame */
+        /* first clean reference cycle through stored exception traceback */
+        PyObject *t, *v, *tb;
+        t = f->f_exc_type;
+        v = f->f_exc_value;
+        tb = f->f_exc_traceback;
+        f->f_exc_type = NULL;
+        f->f_exc_value = NULL;
+        f->f_exc_traceback = NULL;
+        Py_XDECREF(t);
+        Py_XDECREF(v);
+        Py_XDECREF(tb);
+        gen->gi_frame = NULL;
+        Py_DECREF(f);
+    }
+
+    return result;
 }
 
 PyDoc_STRVAR(send_doc,
@@ -83,33 +145,146 @@ PyDoc_STRVAR(close_doc,
  *   close a subiterator being delegated to by yield-from.
  */
 
+static int
+gen_close_iter(PyObject *yf)
+{
+    PyObject *retval = NULL;
+    _Py_IDENTIFIER(close);
+
+    if (PyGen_CheckExact(yf)) {
+        retval = gen_close((PyGenObject *)yf, NULL);
+        if (retval == NULL)
+            return -1;
+    } else {
+        PyObject *meth = _PyObject_GetAttrId(yf, &PyId_close);
+        if (meth == NULL) {
+            if (!PyErr_ExceptionMatches(PyExc_AttributeError))
+                PyErr_WriteUnraisable(yf);
+            PyErr_Clear();
+        } else {
+            retval = PyObject_CallFunction(meth, "");
+            Py_DECREF(meth);
+            if (retval == NULL)
+                return -1;
+        }
+    }
+    Py_XDECREF(retval);
+    return 0;
+}
+
 static PyObject *
 gen_yf(PyGenObject *gen)
 {
+    PyObject *yf = NULL;
     PyFrameObject *f = gen->gi_frame;
-    if (f)
+
-        return _PyFrame_YieldingFrom(f);
+    if (f && f->f_stacktop) {
-    else
+        PyObject *bytecode = f->f_code->co_code;
-        return NULL;
+        unsigned char *code = (unsigned char *)PyBytes_AS_STRING(bytecode);
+
+        if (code[f->f_lasti + 1] != YIELD_FROM)
+            return NULL;
+        yf = f->f_stacktop[-1];
+        Py_INCREF(yf);
+    }
+
+    return yf;
 }
 
 static PyObject *
 gen_close(PyGenObject *gen, PyObject *args)
 {
-    PyFrameObject *f = gen->gi_frame;
+    PyObject *retval;
+    PyObject *yf = gen_yf(gen);
+    int err = 0;
 
-    /* For compatibility, we check gi_running before f == NULL */
+    if (yf) {
-    if (gen->gi_running) {
+        gen->gi_running = 1;
-        PyErr_SetString(PyExc_ValueError,
+        err = gen_close_iter(yf);
-                        "generator already executing");
+        gen->gi_running = 0;
+        Py_DECREF(yf);
+    }
+    if (err == 0)
+        PyErr_SetNone(PyExc_GeneratorExit);
+    retval = gen_send_ex(gen, Py_None, 1);
+    if (retval) {
+        Py_DECREF(retval);
+        PyErr_SetString(PyExc_RuntimeError,
+                        "generator ignored GeneratorExit");
         return NULL;
     }
-    if (f == NULL)
+    if (PyErr_ExceptionMatches(PyExc_StopIteration)
-        Py_RETURN_NONE;
+        || PyErr_ExceptionMatches(PyExc_GeneratorExit)) {
-
+        PyErr_Clear();          /* ignore these errors */
-    return _PyFrame_Finalize(f);
+        Py_INCREF(Py_None);
+        return Py_None;
+    }
+    return NULL;
 }
 
+static void
+gen_del(PyObject *self)
+{
+    PyObject *res;
+    PyObject *error_type, *error_value, *error_traceback;
+    PyGenObject *gen = (PyGenObject *)self;
+
+    if (gen->gi_frame == NULL || gen->gi_frame->f_stacktop == NULL)
+        /* Generator isn't paused, so no need to close */
+        return;
+
+    /* Temporarily resurrect the object. */
+    assert(self->ob_refcnt == 0);
+    self->ob_refcnt = 1;
+
+    /* Save the current exception, if any. */
+    PyErr_Fetch(&error_type, &error_value, &error_traceback);
+
+    res = gen_close(gen, NULL);
+
+    if (res == NULL)
+        PyErr_WriteUnraisable(self);
+    else
+        Py_DECREF(res);
+
+    /* Restore the saved exception. */
+    PyErr_Restore(error_type, error_value, error_traceback);
+
+    /* Undo the temporary resurrection; can't use DECREF here, it would
+     * cause a recursive call.
+     */
+    assert(self->ob_refcnt > 0);
+    if (--self->ob_refcnt == 0)
+        return; /* this is the normal path out */
+
+    /* close() resurrected it!  Make it look like the original Py_DECREF
+     * never happened.
+     */
+    {
+        Py_ssize_t refcnt = self->ob_refcnt;
+        _Py_NewReference(self);
+        self->ob_refcnt = refcnt;
+    }
+    assert(PyType_IS_GC(Py_TYPE(self)) &&
+           _Py_AS_GC(self)->gc.gc_refs != _PyGC_REFS_UNTRACKED);
+
+    /* If Py_REF_DEBUG, _Py_NewReference bumped _Py_RefTotal, so
+     * we need to undo that. */
+    _Py_DEC_REFTOTAL;
+    /* If Py_TRACE_REFS, _Py_NewReference re-added self to the object
+     * chain, so no more to do there.
+     * If COUNT_ALLOCS, the original decref bumped tp_frees, and
+     * _Py_NewReference bumped tp_allocs:  both of those need to be
+     * undone.
+     */
+#ifdef COUNT_ALLOCS
+    --(Py_TYPE(self)->tp_frees);
+    --(Py_TYPE(self)->tp_allocs);
+#endif
+}
+
+
+
 PyDoc_STRVAR(throw_doc,
 "throw(typ[,val[,tb]]) -> raise exception in generator,\n\
 return next yielded value or raise StopIteration.");
@@ -131,7 +306,7 @@ gen_throw(PyGenObject *gen, PyObject *args)
         int err;
         if (PyErr_GivenExceptionMatches(typ, PyExc_GeneratorExit)) {
             gen->gi_running = 1;
-            err = _PyFrame_CloseIterator(yf);
+            err = gen_close_iter(yf);
             gen->gi_running = 0;
             Py_DECREF(yf);
             if (err < 0)
@@ -369,6 +544,7 @@ PyTypeObject PyGen_Type = {
     0,                                          /* tp_cache */
     0,                                          /* tp_subclasses */
     0,                                          /* tp_weaklist */
+    gen_del,                                    /* tp_del */
 };
 
 PyObject *
@@ -380,7 +556,6 @@ PyGen_New(PyFrameObject *f)
         return NULL;
     }
     gen->gi_frame = f;
-    f->f_gen = (PyObject *) gen;
     Py_INCREF(f->f_code);
     gen->gi_code = (PyObject *)(f->f_code);
     gen->gi_running = 0;
@@ -392,5 +567,17 @@ PyGen_New(PyFrameObject *f)
 int
 PyGen_NeedsFinalizing(PyGenObject *gen)
 {
+    int i;
+    PyFrameObject *f = gen->gi_frame;
+
+    if (f == NULL || f->f_stacktop == NULL)
+        return 0; /* no frame or empty blockstack == no finalization */
+
+    /* Any block type besides a loop requires cleanup. */
+    for (i = 0; i < f->f_iblock; i++)
+        if (f->f_blockstack[i].b_type != SETUP_LOOP)
+            return 1;
+
+    /* No blocks except loops, it's safe to skip finalization. */
     return 0;
 }