Increment usage count at first reference, to avoid a race condition with many threads...

(issue #18156)
 Reported by: asgaroth
 Patches:
       20110214__issue18156.diff.txt uploaded by tilghman (license 14)
 Tested by: tilghman

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.6.2@307792 65c4cc65-6c06-0410-ace0-fbb531ad65f3

diff --git a/res/res_odbc.c b/res/res_odbc.c
index a75ed415f9c1028c7b16fc2d1244eec634af837e..c6bbd7a57e2fb76b56c764fafeb0b07c5a81fad1 100644 (file)
--- a/res/res_odbc.c
+++ b/res/res_odbc.c
@@ -1177,10 +1177,11 @@ struct odbc_obj *ast_odbc_request_obj2(const char *name, struct ast_flags flags)
                        ast_assert(ao2_ref(obj, 0) > 1);
                }
 
-               if (!obj && (class->count < class->limit)) {
+               if (!obj && (ast_atomic_fetchadd_int(&class->count, +1) < class->limit)) {
                        obj = ao2_alloc(sizeof(*obj), odbc_obj_destructor);
                        if (!obj) {
                                ao2_ref(class, -1);
+                               ast_atomic_fetchadd_int(&class->count, -1);
                                return NULL;
                        }
                        ast_assert(ao2_ref(obj, 0) == 1);
@@ -1191,14 +1192,18 @@ struct odbc_obj *ast_odbc_request_obj2(const char *name, struct ast_flags flags)
                        if (odbc_obj_connect(obj) == ODBC_FAIL) {
                                ast_log(LOG_WARNING, "Failed to connect to %s\n", name);
                                ao2_ref(obj, -1);
-                               ast_assert(ao2_ref(class, 0) > 0);
                                obj = NULL;
+                               ast_assert(ao2_ref(class, 0) > 0);
+                               ast_atomic_fetchadd_int(&class->count, -1);
                        } else {
                                obj->used = 1;
                                ao2_link(obj->parent->obj_container, obj);
-                               ast_atomic_fetchadd_int(&obj->parent->count, +1);
                        }
                } else {
+                       /* If construction fails due to the limit, remove our increment. */
+                       if (!obj) {
+                               ast_atomic_fetchadd_int(&class->count, -1);
+                       }
                        /* Object is not constructed, so delete outstanding reference to class. */
                        ao2_ref(class, -1);
                        class = NULL;