fix drop hang reported by musicmatze

Fix hang when dropping content needs to lock the content on a ssh remote,
which occurred when the remote has git-annex version 5.20151019 or newer.

Analysis: `race` runs 2 threads at once, and the hGetLine finishes first.
So, it tries to cancel the waitForProcess, but unfortunately that is making
a foreign call and so cannot be canceled. The remote git-annex-shell
is waiting for a line on stdin before it will exit. Deadlock.

This only occurred sometimes; I reproduced it going from darkstar to
elephant, but not from darkstar to darkstar. Not sure how that fits into
the above analysis -- perhaps a race condition is also involved?

Fixed by not using `race`; now the hGetLine will fail with an exception
if the remote git-annex-shell exits without any output.

0 files changed, 0 insertions, 0 deletions