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Checkin Tim's fix to an error discussed on python-dev. 

Also, add a testcase.

Formerly, the list_extend() code used several local variables to remember
its state across iterations.  Since an iteration could call arbitrary
Python code, it was possible for the list state to be changed.  The new
code uses dynamic structure references instead of C locals.  So, they
are always up-to-date.

After list_resize() is called, its size has been updated but the new
cells are filled with NULLs.  These needed to be filled before arbitrary
iteration code was called; otherwise, that code could attempt to modify
a list that was in a semi-invalid state.  The solution was to change
the ob->size field back to a value reflecting the actual number of valid
cells.
This commit is contained in:
Raymond Hettinger 2004-09-26 19:24:20 +00:00
parent 55593c3ef5
commit aa241e0149
2 changed files with 25 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
Lib/test/test_builtin.py
View File

@ -712,6 +712,11 @@ class BuiltinTest(unittest.TestCase):
# http://sources.redhat.com/ml/newlib/2002/msg00369.html
self.assertRaises(MemoryError, list, xrange(sys.maxint // 2))
# This code used to segfault in Py2.4a3
x = []
x.extend(-y for y in x)
self.assertEqual(x, [])
def test_long(self):
self.assertEqual(long(314), 314L)
self.assertEqual(long(3.14), 3L)

30
Objects/listobject.c
View File

@ -769,12 +769,20 @@ listextend(PyListObject *self, PyObject *b)
}
m = self->ob_size;
mn = m + n;
if (list_resize(self, mn) == -1)
goto error;
memset(&(self->ob_item[m]), 0, sizeof(*self->ob_item) * n);
if (mn >= m) {
/* Make room. */
if (list_resize(self, mn) == -1)
goto error;
/* Make the list sane again. */
self->ob_size = m;
}
/* Else m + n overflowed; on the chance that n lied, and there really
* is enough room, ignore it. If n was telling the truth, we'll
* eventually run out of memory during the loop.
*/
/* Run iterator to exhaustion. */
for (i = m; ; i++) {
for (;;) {
PyObject *item = iternext(it);
if (item == NULL) {
if (PyErr_Occurred()) {
@ -785,8 +793,11 @@ listextend(PyListObject *self, PyObject *b)
}
break;
}
if (i < mn)
PyList_SET_ITEM(self, i, item); /* steals ref */
if (self->ob_size < self->allocated) {
/* steals ref */
PyList_SET_ITEM(self, self->ob_size, item);
++self->ob_size;
}
else {
int status = app1(self, item);
Py_DECREF(item); /* append creates a new ref */
@ -796,10 +807,9 @@ listextend(PyListObject *self, PyObject *b)
}
/* Cut back result list if initial guess was too large. */
if (i < mn && self != NULL) {
if (list_ass_slice(self, i, mn, (PyObject *)NULL) != 0)
goto error;
}
if (self->ob_size < self->allocated)
list_resize(self, self->ob_size); /* shrinking can't fail */
Py_DECREF(it);
Py_RETURN_NONE;