code: func (ctrl *PersistentVolumeController) deleteClaim(claim *v1.PersistentVolumeClaim) {
  	_ = ctrl.claims.Delete(claim)
  	klog.V(4).Infof("claim %q deleted", claimToClaimKey(claim))
  
  	volumeName := claim.Spec.VolumeName
  	if volumeName == "" {
  		klog.V(5).Infof("deleteClaim[%q]: volume not bound", claimToClaimKey(claim))
  		return
  	}
  	// sync the volume when its claim is deleted.  Explicitly sync'ing the
  	// volume here in response to claim deletion prevents the volume from
  	// waiting until the next sync period for its Release.
  	klog.V(5).Infof("deleteClaim[%q]: scheduling sync of volume %s", claimToClaimKey(claim), volumeName)
  	ctrl.volumeQueue.Add(volumeName)
  }
docs: // deleteClaim runs in worker thread and handles "claim deleted" event.