On Wed, Nov 25, 2020 at 08:37:02PM +0100, Michal Prívozník wrote: > On 11/25/20 7:04 PM, Daniel P. Berrangé wrote: > > I previously did a workaround for a glib event loop race > > that causes crashes: > > > > commit 0db4743645b7a0611a3c0687f834205c9956f7fc > > Author: Daniel P. Berrangé <berra...@redhat.com> > > Date: Tue Jul 28 16:52:47 2020 +0100 > > > > util: avoid crash due to race in glib event loop code > > > > it turns out that the workaround has a significant performance > > penalty on I/O intensive workloads. We thus need to avoid the > > workaround if we know we have a new enough glib to avoid the > > race condition. > > > > Signed-off-by: Daniel P. Berrangé <berra...@redhat.com> > > --- > > src/util/vireventglib.c | 29 +++++++++++++++++++++-------- > > 1 file changed, 21 insertions(+), 8 deletions(-) > > > > diff --git a/src/util/vireventglib.c b/src/util/vireventglib.c > > index 6842c6e806..8c5495bfab 100644 > > --- a/src/util/vireventglib.c > > +++ b/src/util/vireventglib.c > > @@ -189,9 +189,21 @@ virEventGLibHandleFind(int watch) > > * If the last reference to a GSource is released in a non-main > > * thread we're exposed to a race condition that causes a > > * crash: > > - * https://gitlab.gnome.org/GNOME/glib/-/merge_requests/1358 > > - * Thus we're using an idle func to release our ref > > + * > > + * https://gitlab.gnome.org/GNOME/glib/-/merge_requests/1358 > > + * > > + * Thus we're using an idle func to release our ref... > > + * > > + * ...but this imposes a significant performance penalty on > > + * I/O intensive workloads which are sensitive to the iterations > > + * of the event loop, so avoid the workaround if we know we have > > + * new enough glib. > > */ > > +#if GLIB_CHECK_VERSION(2, 64, 0) > > +# define g_vir_source_unref_safe(source) g_source_unref(source) > > +#else > > +# define g_vir_source_unref_safe(source) > > g_idle_add(virEventGLibSourceUnrefIdle, source); > > s/;// > > > + > > Would something like the following be totally disgusting or only a bit? > > #if !GLIB_CHECK_VERSION(2, 64, 0) > # define g_source_unref(source) g_idle_add(virEventGLibSourceUnrefIdle, > source) > #endif > > - g_idle_add(...); > + g_source_unref(...); > > > This way we could just drop the redefine once we upgrade min glib version.
it is possible, but the hack with g_idle_add is semantically different enough from g_source_unref that I want people to know that something unusal is going on when reading the code. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
