[golang] defer在mutex中用法

• defer可以在mutex lock之后，unlock

type MetaDb struct {
    consul     *gokit.Consul
    identifier CloudIdentifier
    mutex      *sync.RWMutex
    set        *DbSet
}

func (m *MetaDb) Region() Region {
    m.mutex.RLock()
    defer m.mutex.RUnlock()
    return m.set.Region
}