Alright, after some discussions with Ryan, I had a look into this again, and I have now fixed the problem in compiz. Some notes about this:
* DBUS_SESSION_BUS_ADDRESS in the program's env isn't mandatory, since dbus can scrape that information from the root window property if it has X11 support * DBUS_SESSION_BUS_ADDRESS *won't* appear in the program env if it was launched from a VT or SSH or something * Compiz issues an UngrabServer request right after doing XQueryTree, and then initializes plugin screens right afterwards (before initializing every window). * UngrabServer isn't a synchronous operation, so there's a race for the X Server to process that in time * On CcpScreen's ctor, it will initialize libcompizconfig which loads backends (gconf) * GConf initializes and starts DBus to get a connection with the gconf server * GDbus sees that DBUS_SESSION_BUS_ADDRESS isn't set and calls dbus-launch --autolaunch to try and get the bus address * dbus-launch --autolaunch calls get_bus_address_platform_specific (X11 backend) which calls XOpenDisplay () and XGetWindowProperty () to try and get the session bus address from the window prop * The UngrabServer request hasn't been processed yet, so XOpenDisplay instantly fails * GDbus is using g_spawn_sync incorrectly and doesn't restore normal child handling, so when the child process dbus-launch fails to return an address (very rare case), it just blocks forever until glib times out the request. This is what causes the apparent hang, then crash 2 minutes later All of the items above the last one have been fixed compiz-side so this is no longer an issue (though it does pose an interesting problem that trying to get the session bus address while a server grab is active will fail - that is probably a bad thing and should be resolved, maybe a temp socket file should be created in the user's homedir?). Anyways, I believe that while the last item is essentially a corner-case, it still prints an interesting debug message if the command failed to get the bus address and should be fixed. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/690239 Title: hang in g_spawn_sync and select() -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
