Try to avoid creating reference cycles involving generators. Only keep a

reference to f_back when its really needed.  Do a little whitespace
normalization as well.  This whole file is a big war between tabs and spaces
but now is probably not the time to reindent everything.

diff --git a/Python/ceval.c b/Python/ceval.c
index ea5c5378995a8c492dc6db60a753461e1890e498..a71d48f03b2b979efebe121b05138020043985c6 100644 (file)
--- a/Python/ceval.c
+++ b/Python/ceval.c
@@ -138,6 +138,7 @@ gen_dealloc(genobject *gen)
 static PyObject *
 gen_iternext(genobject *gen)
 {
+       PyThreadState *tstate = PyThreadState_GET();
        PyFrameObject *f = gen->frame;
        PyObject *result;
 
@@ -149,15 +150,24 @@ gen_iternext(genobject *gen)
        if (f->f_stackbottom == NULL) {
                return NULL;
        }
-        gen->running = 1;
+
+       /* Generators always return to their most recent caller, not
+        * necessarily their creator. */
+       Py_INCREF(tstate->frame);
+       assert(f->f_back == NULL);
+       f->f_back = tstate->frame;
+
+       gen->running = 1;
        result = eval_frame(f);
-        gen->running = 0;
-        /* The connection between this frame and its parent is over now, so
-           must NULL out f_back lest it get decref'ed when gen dies (note
-           that eval_frame sets f->f_back without bumping its refcount:  we
-           never had a fully legit reference to it). */
+       gen->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. */
+       Py_DECREF(f->f_back);
        f->f_back = NULL;
-        return result;
+
+       return result;
 }
 
 static PyObject *
@@ -168,12 +178,12 @@ gen_next(genobject *gen, PyObject *args)
        if (!PyArg_ParseTuple(args, ":next"))
                return NULL;
 
-        result = gen_iternext(gen);
+       result = gen_iternext(gen);
 
-        if (result == NULL && !PyErr_Occurred()) {
+       if (result == NULL && !PyErr_Occurred()) {
                PyErr_SetObject(PyExc_StopIteration, Py_None);
                return NULL;
-        }
+       }
 
        return result;
 }
@@ -568,9 +578,7 @@ eval_frame(PyFrameObject *f)
                return NULL;
        }
 
-       f->f_back = tstate->frame;
        tstate->frame = f;
-
        co = f->f_code;
        fastlocals = f->f_localsplus;
        freevars = f->f_localsplus + f->f_nlocals;
@@ -2482,8 +2490,13 @@ eval_code2(PyCodeObject *co, PyObject *globals, PyObject *locals,
        }
 
        if (co->co_flags & CO_GENERATOR) {
-                /* create a new generator that owns the ready to run frame
-                 * and return that as the value */
+               /* Don't need to keep the reference to f_back, it will be set
+                * when the generator is resumed. */
+               Py_DECREF(f->f_back);
+               f->f_back = NULL;
+
+               /* Create a new generator that owns the ready to run frame
+                * and return that as the value. */
                return gen_new(f);
        }