// addRelation causes the unit agent to join the supplied relation, and to
// store persistent state in the supplied dir.
func (u *Uniter) addRelation(rel *state.Relation, dir *relation.StateDir) error {
log.Printf("worker/uniter: joining relation %q", rel)
ru, err := rel.Unit(u.unit)
if err != nil {
return err
}
r := NewRelationer(ru, dir, u.relationHooks)
w := u.unit.Watch()
defer watcher.Stop(w, &u.tomb)
for {
select {
case <-u.tomb.Dying():
return tomb.ErrDying
case _, ok := <-w.Changes():
if !ok {
return watcher.MustErr(w)
}
if err := r.Join(); err == state.ErrCannotEnterScopeYet {
log.Printf("worker/uniter: cannot enter scope for relation %q; waiting for subordinate to be removed", rel)
continue
} else if err != nil {
return err
}
log.Printf("worker/uniter: joined relation %q", rel)
u.relationers[rel.Id()] = r
return nil
}
}
panic("unreachable")
}
