SF bug 543148: Memory leak with stackframes + inspect.

Put a bound on the number of frameobjects that can live in the
frameobject free_list.

Am also backporting to 2.2.  I don't intend to backport to 2.1 (too
much work -- lots of cyclic structures leak there, and the GC API).

diff --git a/Objects/frameobject.c b/Objects/frameobject.c
index 8e4c60ff2722a2af20498998122e8c981544b71e..165121d8f8715505ff3254e28a9fd23136438c95 100644 (file)
--- a/Objects/frameobject.c
+++ b/Objects/frameobject.c
@@ -56,9 +56,15 @@ static PyGetSetDef frame_getsetlist[] = {
    After all, while a typical program may make millions of calls, a
    call depth of more than 20 or 30 is probably already exceptional
    unless the program contains run-away recursion.  I hope.
+
+   Later, MAXFREELIST was added to bound the # of frames saved on
+   free_list.  Else programs creating lots of cyclic trash involving
+   frames could provoke free_list into growing without bound.
 */
 
 static PyFrameObject *free_list = NULL;
+static int numfree = 0;                /* number of frames currently in free_list */
+#define MAXFREELIST 200                /* max value for numfree */
 
 static void
 frame_dealloc(PyFrameObject *f)
@@ -91,8 +97,13 @@ frame_dealloc(PyFrameObject *f)
        Py_XDECREF(f->f_exc_type);
        Py_XDECREF(f->f_exc_value);
        Py_XDECREF(f->f_exc_traceback);
-       f->f_back = free_list;
-       free_list = f;
+       if (numfree < MAXFREELIST) {
+               ++numfree;
+               f->f_back = free_list;
+               free_list = f;
+       }
+       else
+               PyObject_GC_Del(f);
        Py_TRASHCAN_SAFE_END(f)
 }
 
@@ -245,6 +256,8 @@ PyFrame_New(PyThreadState *tstate, PyCodeObject *code, PyObject *globals,
                        return NULL;
        }
        else {
+               assert(numfree > 0);
+               --numfree;
                f = free_list;
                free_list = free_list->f_back;
                if (f->ob_size < extras) {
@@ -475,5 +488,7 @@ PyFrame_Fini(void)
                PyFrameObject *f = free_list;
                free_list = free_list->f_back;
                PyObject_GC_Del(f);
+               --numfree;
        }
+       assert(numfree == 0);
 }