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

Barry Warsaw barry at python.org
Fri Apr 13 17:22:34 CEST 2007

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On Apr 13, 2007, at 11:07 AM, Jean-Paul Calderone wrote:

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 ;).

Seems plausible to me too. If I change the child writes to > 4000
bytes, Linux w/2.6 kernel will block too.

I'm going to change the test_pty.py code to read from the master_fd.
You have to wrap the read in a try/except to catch the OSError input/ output error you'll get on Linux when you read past the end of the
buffer and the child process has already exited.

Thanks,

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