[Python-Dev] test_pty.py hangs in verbose mode on Mac OS X? (original) (raw)

Barry Warsaw barry at python.org
Fri Apr 13 17:02:01 CEST 2007

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On Apr 13, 2007, at 10:57 AM, Jean-Paul Calderone wrote:

I don't know if this is caused by a bug in the Mac's pty implementation or something we're doing wrong on that platform. I played around with several modifications to pty.fork() on the Mac, including letting it drop down to the openpty()/os.fork() code, even adding an explicit ioctl(slavefd, TIOCSCTTY) call which Stevens chapter 19 recommends for 4.3+BSD. I can't get it to not block. What about reading from the child in the parent before calling waitpid?

Yep, this is what I suggested below. Porting the same change over to
Linux produced an OSError, but that's probably just because I wasn't
as careful as I should have been late last night.

Barring a fix to pty.fork() (or possibly os.forkpty()) for the Mac, then I would like to at least make testpty.py not block when run in verbose mode. A very simple hack would add something like this to the "if pid == pty.CHILD" stanza: "def debug(msg): pass", possibly protected by a "if verbose:". A less icky hack would be to read the output from the masterfd in the parent, though you have to be careful with that on Linux else the read can throw an input/output error.

Disabling debug output is band-aid yes, and any application on the Mac like the above snippet will still fail. If anybody has any suggestions, I'm all ears, but I've reached the limit of my pty-fu. I don't think this is an OS X PTY bug. Writing to a blocking file descriptor can block. Programs that do this need to account for the possibility.

Why doesn't it block on Linux then?

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