Priority queue from: https://github.com/mreiferson/go-httpclient/tree/go11_11/pqueue
Documentation: http://godoc.org/github.com/facebookgo/pqueue
Priority queue from: https://github.com/mreiferson/go-httpclient/tree/go11_11/pqueue
Documentation: http://godoc.org/github.com/facebookgo/pqueue