[Python-Dev] Small memory leak in unicodeobject.c

[Barry A. Warsaw]

I've found a small memory leak in unicodeobject.c, in the way
_PyUnicode_Fini() shuts down.  Take a loop such as:

-------------------- snip snip --------------------
#include "Python.h"

int main(int argc, char** argv)
{
    int i;

    while (1) {
        Py_Initialize();
        Py_Finalize();
    }
    return 0;
}
-------------------- snip snip --------------------

and you'll find that unicode_empty leaks.  This is because, while
_PyUnicode_Fini() decrefs unicode_empty, it never actually gets
freed.  Instead it gets placed on the already freed unicode_freelist!
See _PyUnicode_Free() for why.

I've come up with the following nasty hack to force unicode_empty to
really be freed in _PyUnicode_Fini().  Maybe there's a better way to
do this.  Note that moving the decref of unicode_empty to above the
freeing of unicode_freelist didn't plug the memory leak for me (but
I'm quite tired so maybe I missed something! ;} ).

Below is the proposed patch.
-Barry

-------------------- snip snip --------------------
Index: unicodeobject.c
===================================================================
RCS file: /cvsroot/python/python/dist/src/Objects/unicodeobject.c,v
retrieving revision 2.64
diff -u -r2.64 unicodeobject.c
--- unicodeobject.c	2000/09/26 05:46:01	2.64
+++ unicodeobject.c	2000/10/03 16:31:32
@@ -5234,7 +5234,11 @@
 	PyObject_DEL(v);
     }
     unicode_freelist = NULL;
-    unicode_freelist_size = 0;
+    /* XXX This is a hack to force the freeing of unicode_empty's memory.
+     * Otherwise, it'll get placed on the already freed free list.
+     */
+    unicode_freelist_size = MAX_UNICODE_FREELIST_SIZE;
     Py_XDECREF(unicode_empty);
     unicode_empty = NULL;
+    unicode_freelist_size = 0;
 }