pool

type DnsPool interface {
	// thread safe, will block until a connection is available
	// creates new connections until the pool is full
	Get() (*dns.Conn, error)
	// return a connection to the pool and handle network appropriate actions
	// a tcp connection will be retained, a udp connection will be closed and not reused
	// this is thread-safe but not for a given connection (which is ok because two threads probably shouldn't try and release the same connection at the same time)
	Release(conn *dns.Conn)
	// discard a connection and remove it from the pool (used for error'd connections)
	// this is thread-safe but not for a given connection (which is ok because two threads probably shouldn't try and discard the same connection at the same time)
	Discard(conn *dns.Conn)
	// shutdown enables a clean/safe shutdown of the pool
	Shutdown()
}

type DnsPoolConfiguration struct {
	// max connections this pool can hand out
	MaxConnections int
}