Issue #475

Fix a crash that can occur only if there is an error when building a callback
(in very rare cases), or in debug mode.

2 files changed, 3 insertions, 2 deletions

diff --git a/c/_cffi_backend.c b/c/_cffi_backend.c
index ecf0c8f..c9919ab 100644
--- a/c/_cffi_backend.c
+++ b/c/_cffi_backend.c
@@ -6299,8 +6299,8 @@ static PyObject *b_callback(PyObject *self, PyObject *args)
     cd->head.c_type = ct;
     cd->head.c_data = (char *)closure_exec;
     cd->head.c_weakreflist = NULL;
+    closure->user_data = NULL;
     cd->closure = closure;
-    PyObject_GC_Track(cd);
 
     cif_descr = (cif_description_t *)ct->ct_extra;
     if (cif_descr == NULL) {
@@ -6357,6 +6357,7 @@ static PyObject *b_callback(PyObject *self, PyObject *args)
             "different from the 'ffi.h' file seen at compile-time)");
         goto error;
     }
+    PyObject_GC_Track(cd);
     return (PyObject *)cd;
 
  error:
diff --git a/c/test_c.py b/c/test_c.py
index 643cc90..bb6b586 100644
--- a/c/test_c.py
+++ b/c/test_c.py
@@ -1470,7 +1470,7 @@ def test_a_lot_of_callbacks():
     def make_callback(m):
         def cb(n):
             return n + m
-        return callback(BFunc, cb, 42)    # 'cb' and 'BFunc' go out of scope
+        return callback(BFunc, cb, 42)    # 'cb' goes out of scope
     #
     flist = [make_callback(i) for i in range(BIGNUM)]
     for i, f in enumerate(flist):