On Fri, 13 Apr 2007 11:02:01 -0400, Barry Warsaw <[EMAIL PROTECTED]> wrote: >-----BEGIN PGP SIGNED MESSAGE----- >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? >
Likely differing buffering behavior. Prior to Linux 2.6, the pipe implementation allowed only a single buffer (that is, the bytes from a single write call) in a pipe at a time, and blocked subsequent writes until that buffer was read. Recently this has changed to allow multiple buffers up to 4k total length, so multiple short writes won't block anymore. OS X may have some other buffering behavior which is causing writes to block where they don't on Linux. All these details are left to the platform, and there are a variety of behaviors which can be considered valid. Of course, I don't actually /know/ the cause of the problem here, but this explanation seems plausible to me, and I'd investigate it before looking for platform-specific pty bugs (although OS X is a good platform on which to go looking for those ;). Jean-Paul _______________________________________________ Python-Dev mailing list [EMAIL PROTECTED] http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
