Barriers can only be created on the top thread
Barriers can only be created on the top thread

This is similar ASSERT_CLI, in order to make socket barriers creation
thread-safe.

feld/Varnish-Cache,feld/Varnish-Cache,gquintard/Varnish-Cache,gquintard/Varnish-Cache,feld/Varnish-Cache,feld/Varnish-Cache,gquintard/Varnish-Cache,gquintard/Varnish-Cache,feld/Varnish-Cache