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 <berrange@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 <berrange@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 :|