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Sub-jobs, and bi-directional i/o.

    Date: 26 December 1980 2158-EST (Friday)
    From: Leonard.Zubkoff at CMU-10A (C410LZ60)
    Subject:  PTYs in LISP
    Message-Id: <26Dec80 215856 LZ60@CMU-10A>
    I have been trying to open a PTY for both input and output in order to 
    control a subjob from LISP on CMU-20C (TOPS-20) with no success.  I 
    receive an invalid simultaneous access error whenever I try this.  Is 
    there a way to control a sub job through PTYs in LISP on the 20?  Thanks.
    -  -  -  -  
    Date: 26 December 1980 2300-EST
    From: Dave Touretzky at CMU-10A
    Why bother?  Since you're running on the 20, wouldn't the SUBFORK package
    do what you needed?
    MacLisp i/o seems to be somewhat wedged in that you cannot do input and
    output through the same file object (as far as I know.)  This means that
    you can't open a random access file for "update", i.e. read followed by
    write.  Perhaps the same lossage is responsible for your PTY difficulties.
True, a subforking would be much better than a PTY.  However, one could use
a SFA to combind two file-arrays into one file-like object (the sfa) thru
which you could do bi-directional i/o.  See the example in the file
MC:LSPSRC;YESNOP >   -- the function QUERY-IO-HANDLER is the sfa function
which is set up later in the file (look for the usage of sfa-create).