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

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

Hash: SHA1

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(slave_fd, 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 test_pty.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 master_fd 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?

- -Barry

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