fix rare GC issue during type creation (fixes #277)

docs/changelog.rst

@@ -21,12 +21,15 @@ Breaking changes queued for v2.0.0 (Not yet released)
 * Added ``eval`` and ``eval_file`` functions for evaluating expressions and
   statements from a string or file
 * eigen.h type converter fixed for non-contiguous arrays (e.g. slices)
-* print more informative error messages when ``make_tuple()`` or ``cast()`` fail
+* Print more informative error messages when ``make_tuple()`` or ``cast()`` fail
 * ``std::enable_shared_from_this<>`` now also works for ``const`` values
-* a return value policy can now be passed to ``handle::operator()``
+* A return value policy can now be passed to ``handle::operator()``
-* ``make_iterator()`` improvements for better compatibility with various types (now uses prefix increment operator)
+* ``make_iterator()`` improvements for better compatibility with various types
+  (now uses prefix increment operator)
 * ``arg()`` now accepts a wider range of argument types for default values
-* various minor improvements of library internals (no user-visible changes)
+* Fixed a rare but potentially very severe issue when the garbage collector ran
+  during pybind11 type creation.
+* Various minor improvements of library internals (no user-visible changes)
 
 1.8.0 (June 14, 2016)
 ----------------------

include/pybind11/pybind11.h

@@ -559,8 +559,40 @@ protected:
             pybind11_fail("generic_type: type \"" + std::string(rec->name) +
                           "\" is already registered!");
 
-        object type_holder(PyType_Type.tp_alloc(&PyType_Type, 0), false);
         object name(PYBIND11_FROM_STRING(rec->name), false);
+        object scope_module;
+        if (rec->scope) {
+            scope_module = (object) rec->scope.attr("__module__");
+            if (!scope_module)
+                scope_module = (object) rec->scope.attr("__name__");
+        }
+
+#if PY_MAJOR_VERSION >= 3 && PY_MINOR_VERSION >= 3
+        /* Qualified names for Python >= 3.3 */
+        object scope_qualname;
+        if (rec->scope)
+            scope_qualname = (object) rec->scope.attr("__qualname__");
+        object ht_qualname;
+        if (scope_qualname) {
+            ht_qualname = object(PyUnicode_FromFormat(
+                "%U.%U", scope_qualname.ptr(), name.ptr()), false);
+        } else {
+            ht_qualname = name;
+        }
+#endif
+        std::string full_name = (scope_module ? ((std::string) scope_module.str() + "." + rec->name)
+                                              : std::string(rec->name));
+
+        char *tp_doc = nullptr;
+        if (rec->doc) {
+            /* Allocate memory for docstring (using PyObject_MALLOC, since
+               Python will free this later on) */
+            size_t size = strlen(rec->doc) + 1;
+            tp_doc = (char *) PyObject_MALLOC(size);
+            memcpy((void *) tp_doc, rec->doc, size);
+        }
+
+        object type_holder(PyType_Type.tp_alloc(&PyType_Type, 0), false);
         auto type = (PyHeapTypeObject*) type_holder.ptr();
 
         if (!type_holder || !name)
@@ -574,36 +606,18 @@ protected:
         internals.registered_types_cpp[tindex] = tinfo;
         internals.registered_types_py[type] = tinfo;
 
-        object scope_module;
-        if (rec->scope) {
-            scope_module = (object) rec->scope.attr("__module__");
-            if (!scope_module)
-                scope_module = (object) rec->scope.attr("__name__");
-        }
-
-        std::string full_name = (scope_module ? ((std::string) scope_module.str() + "." + rec->name)
-                                              : std::string(rec->name));
         /* Basic type attributes */
         type->ht_type.tp_name = strdup(full_name.c_str());
         type->ht_type.tp_basicsize = (ssize_t) rec->instance_size;
         type->ht_type.tp_base = (PyTypeObject *) rec->base_handle.ptr();
         rec->base_handle.inc_ref();
 
-#if PY_MAJOR_VERSION >= 3 && PY_MINOR_VERSION >= 3
-        /* Qualified names for Python >= 3.3 */
-        object scope_qualname;
-        if (rec->scope)
-            scope_qualname = (object) rec->scope.attr("__qualname__");
-        if (scope_qualname) {
-            type->ht_qualname = PyUnicode_FromFormat(
-                "%U.%U", scope_qualname.ptr(), name.ptr());
-        } else {
-            type->ht_qualname = name.ptr();
-            name.inc_ref();
-        }
-#endif
         type->ht_name = name.release().ptr();
 
+#if PY_MAJOR_VERSION >= 3 && PY_MINOR_VERSION >= 3
+        type->ht_qualname = ht_qualname.release().ptr();
+#endif
+
         /* Supported protocols */
         type->ht_type.tp_as_number = &type->as_number;
         type->ht_type.tp_as_sequence = &type->as_sequence;
@@ -624,13 +638,7 @@ protected:
 #endif
         type->ht_type.tp_flags &= ~Py_TPFLAGS_HAVE_GC;
 
-        if (rec->doc) {
+        type->ht_type.tp_doc = tp_doc;
-            /* Allocate memory for docstring (using PyObject_MALLOC, since
-               Python will free this later on) */
-            size_t size = strlen(rec->doc) + 1;
-            type->ht_type.tp_doc = (char *) PyObject_MALLOC(size);
-            memcpy((void *) type->ht_type.tp_doc, rec->doc, size);
-        }
 
         if (PyType_Ready(&type->ht_type) < 0)
             pybind11_fail("generic_type: PyType_Ready failed!");
@@ -654,17 +662,21 @@ protected:
 
         if (ob_type == &PyType_Type) {
             std::string name_ = std::string(ht_type.tp_name) + "__Meta";
-            object type_holder(PyType_Type.tp_alloc(&PyType_Type, 0), false);
+#if PY_MAJOR_VERSION >= 3 && PY_MINOR_VERSION >= 3
+            object ht_qualname(PyUnicode_FromFormat(
+                "%U__Meta", ((object) attr("__qualname__")).ptr()), false);
+#endif
             object name(PYBIND11_FROM_STRING(name_.c_str()), false);
+            object type_holder(PyType_Type.tp_alloc(&PyType_Type, 0), false);
             if (!type_holder || !name)
                 pybind11_fail("generic_type::metaclass(): unable to create type object!");
 
             auto type = (PyHeapTypeObject*) type_holder.ptr();
             type->ht_name = name.release().ptr();
+
 #if PY_MAJOR_VERSION >= 3 && PY_MINOR_VERSION >= 3
             /* Qualified names for Python >= 3.3 */
-            type->ht_qualname = PyUnicode_FromFormat(
+            type->ht_qualname = ht_qualname.release().ptr();
-                "%U__Meta", ((object) attr("__qualname__")).ptr());
 #endif
             type->ht_type.tp_name = strdup(name_.c_str());
             type->ht_type.tp_base = ob_type;