Make guard reentrant
Make guard reentrant

crossbeam-rs/crossbeam,crossbeam-rs/crossbeam,steveklabnik/crossbeam,crossbeam-rs/crossbeam,ticki/baguette,crossbeam-rs/crossbeam,Ticki/crossbeam,aturon/crossbeam,phil-opp/crossbeam,huonw/crossbeam,schets/crossbeam,msullivan/crossbeam,alexcrichton/crossbeam