Eliminates a race condition accessing DBusBabysitter instance at startup of babysitte...

Ensure that the babysitter thread already owns its one reference to the
babysitter when it starts up, and eliminates the race condition.
This patch requires that DBusBabysitter refcounting is thread-safe
and is based on an analysis and proposal of Simon Mc Vittie.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=95191
Reviewed-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

diff --git a/dbus/dbus-spawn-win.c b/dbus/dbus-spawn-win.c
index 804aa4269e0030065deb51fec7c326db85866523..fa2906386f702e820d5cfa0a04abaf35a64ec7d6 100644 (file)
--- a/dbus/dbus-spawn-win.c
+++ b/dbus/dbus-spawn-win.c
@@ -586,8 +586,6 @@ babysitter (void *parameter)
   DBusBabysitter *sitter = (DBusBabysitter *) parameter;
 
   PING();
-  _dbus_babysitter_ref (sitter);
-
   if (sitter->child_setup)
     {
       PING();
@@ -728,7 +726,7 @@ _dbus_spawn_async_with_babysitter (DBusBabysitter           **sitter_p,
 
   PING();
   sitter_thread = (HANDLE) CreateThread (NULL, 0, babysitter,
-                  sitter, 0, &sitter_thread_id);
+                  _dbus_babysitter_ref (sitter), 0, &sitter_thread_id);
 
   if (sitter_thread == 0)
     {