Re: [libvirt PATCH 2/2] util: avoid glib event loop workaround where possible

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 <berrange(a)redhat.com&gt; > 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 <berrange(a)redhat.com&gt; > --- > 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.