Issue #17807: Generators can now be finalized even when they are part of a reference cycle.
diff --git a/Objects/frameobject.c b/Objects/frameobject.c
index 6fff370..df7a1de0 100644
--- a/Objects/frameobject.c
+++ b/Objects/frameobject.c
@@ -31,6 +31,195 @@
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)
{
@@ -420,32 +609,43 @@
#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)
@@ -497,12 +697,25 @@
{
PyObject **fastlocals, **p, **oldtop;
Py_ssize_t i, slots;
+ PyObject *retval;
- /* Before anything else, make sure that this frame is clearly marked
- * as being defunct! Else, e.g., a generator reachable from this
- * frame may also point to this frame, believe itself to still be
- * active, and try cleaning up this frame again.
- */
+ if (f->f_back == NULL) {
+ PyObject *t, *v, *tb;
+ PyErr_Fetch(&t, &v, &tb);
+ /* Note that this can finalize a suspended generator frame even
+ * 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;
@@ -713,6 +926,7 @@
f->f_lasti = -1;
f->f_lineno = code->co_firstlineno;
f->f_iblock = 0;
+ f->f_gen = NULL;
_PyObject_GC_TRACK(f);
return f;
diff --git a/Objects/genobject.c b/Objects/genobject.c
index 016bfa2..34ecf2c 100644
--- a/Objects/genobject.c
+++ b/Objects/genobject.c
@@ -19,112 +19,50 @@
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);
- _PyObject_GC_TRACK(self);
-
- if (gen->gi_frame != NULL && gen->gi_frame->f_stacktop != NULL) {
- /* Generator is paused, so we need to close */
- Py_TYPE(gen)->tp_del(self);
- if (self->ob_refcnt > 0)
- return; /* resurrected. :( */
+ gen->gi_frame = NULL;
+ if (f) {
+ /* Close the generator by finalizing the frame */
+ PyObject *retval, *t, *v, *tb;
+ PyErr_Fetch(&t, &v, &tb);
+ f->f_gen = NULL;
+ retval = _PyFrame_Finalize(f);
+ 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 || f->f_stacktop == NULL) {
- /* Only set exception if called from send() */
+ if (f == 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;
-
- 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;
+ return _PyFrame_GeneratorSend(f, arg, exc);
}
PyDoc_STRVAR(send_doc,
@@ -145,146 +83,33 @@
* 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 && 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;
+ if (f)
+ return _PyFrame_YieldingFrom(f);
+ else
+ return NULL;
}
static PyObject *
gen_close(PyGenObject *gen, PyObject *args)
{
- PyObject *retval;
- PyObject *yf = gen_yf(gen);
- int err = 0;
+ PyFrameObject *f = gen->gi_frame;
- if (yf) {
- gen->gi_running = 1;
- err = gen_close_iter(yf);
- 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");
+ /* For compatibility, we check gi_running before f == NULL */
+ if (gen->gi_running) {
+ PyErr_SetString(PyExc_ValueError,
+ "generator already executing");
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;
+ if (f == NULL)
+ Py_RETURN_NONE;
+
+ return _PyFrame_Finalize(f);
}
-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.");
@@ -306,7 +131,7 @@
int err;
if (PyErr_GivenExceptionMatches(typ, PyExc_GeneratorExit)) {
gen->gi_running = 1;
- err = gen_close_iter(yf);
+ err = _PyFrame_CloseIterator(yf);
gen->gi_running = 0;
Py_DECREF(yf);
if (err < 0)
@@ -544,7 +369,6 @@
0, /* tp_cache */
0, /* tp_subclasses */
0, /* tp_weaklist */
- gen_del, /* tp_del */
};
PyObject *
@@ -556,6 +380,7 @@
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;
@@ -567,17 +392,5 @@
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;
}