When I played with blackhole's "bh install" command in osx, it stops at "Downloading packages".
After I look into the source code, it seems the call to "with-output-to-process" in "untar" function causes this.

Below are code I wrote to reproduce the problem

(with-output-to-process
  (list path: "sed"
        arguments: '("-e" "s/n/N/g"))
  (lambda ()
    (display "nothing")))

--
Zhang Meng
School of Software Engineering, Tongji University
MP: +86 151-2103-2798