windows: allow readpipe() to actually read data out of the pipe It appears that the read() in readpipe() never actually ran before (in test-ssh.t anyway). A print of the size returned from os.fstat() is 0 for every single print output in test-ssh.t, so the data in the pipe ends up being read later instead of when it is available. This is the same problem as Linux, as mentioned in 331cbf088c4c. There are several places in the Windows SSH tests where the order of local output vs remote output differ from the other platforms. This only fixes one of those cases (and interstingly, not the one added in order to test 331cbf088c4c), so there is more investigation needed. However, without this patch, test-ssh.t also has this diff: --- c:/Users/Matt/Projects/hg/tests/test-ssh.t +++ c:/Users/Matt/Projects/hg/tests/test-ssh.t.err @@ -397,11 +397,11 @@ $ hg push --ssh "sh ../ssh.sh" pushing to ssh://user@dummy/*/remote (glob) searching for changes - remote: Permission denied - remote: abort: prechangegroup.hg-ssh hook failed - remote: Permission denied - remote: pushkey-abort: prepushkey.hg-ssh hook failed updating 6c0482d977a3 to public failed! + remote: Permission denied + remote: abort: prechangegroup.hg-ssh hook failed + remote: Permission denied + remote: pushkey-abort: prepushkey.hg-ssh hook failed [1] $ cd .. Output with this change was stable over 600+ runs of test-ssh.t. I initially tried a background thread to read the pipe[1], but this was simpler and the test results were exactly the same. I also tried SetNamedPipeHandleState(), but the PIPE_NOWAIT is for compatibility with LANMAN 2.0, not for async I/O (the results were identical though). [1] http://eyalarubas.com/python-subproc-nonblock.html