There is a fairly long standing race condition bug in glib which can hit
if you call g_source_destroy or g_source_unref from a non-main thread:
https://gitlab.gnome.org/GNOME/glib/-/merge_requests/1358
Unfortunately it is really common for libvirt to call g_source_destroy
from a non-main thread. This glib bug is the cause of non-determinstic
crashes in eventtest, and probably in libvirtd too.
To work around the problem we need to ensure that we never release
the last reference on a GSource from a non-main thread. The previous
patch replaced our use of g_source_destroy with a pair of
g_source_remove and g_source_unref. We can now delay the g_source_unref
call by using a idle callback to invoke it from the main thread which
avoids the race condition.
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
The source ID number is an alternative way to identify a source that has
been added to a GMainContext. Internally when a source ID is given, glib
will lookup the corresponding GSource and use that. The use of a source
ID is racy in some cases though, because it is invalid to continue to
use an ID number after the GSource has been removed. It is thus safer
to use the GSource object directly and have full control over the ref
counting and thus cleanup.
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
The libvirt-glib project has provided a GMainContext based
event loop impl for applications. This imports it and sets
it up for use by libvirt as the primary event loop. This
remains a private impl detail of libvirt.
IOW, applications must *NOT* assume that a call to
"virEventRegisterDefaultImpl" results in a GLib based
event loop. They should continue to use the libvirt-glib
API gvir_event_register() if they explicitly want to
guarantee a GLib event loop.
This follows the general principle that the libvirt public
API should not expose the fact that GLib is being used
internally.
Reviewed-by: Pavel Hrdina <phrdina@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
