code: func (p *Pss) cleanFwdCache() {
  	metrics.GetOrRegisterCounter("pss.cleanfwdcache", nil).Inc(1)
  	p.fwdCacheMu.Lock()
  	defer p.fwdCacheMu.Unlock()
  	for k, v := range p.fwdCache {
  		if v.expiresAt.Before(time.Now()) {
  			delete(p.fwdCache, k)
  		}
  	}
  }
docs: /////////////////////////////////////////////////////////////////////
  // SECTION: Caching
  /////////////////////////////////////////////////////////////////////
  // cleanFwdCache is used to periodically remove expired entries from the forward cache