MACD 5/MACD 5.bin/workbench/tools/czesc_2/fifolib/fifo.doc

Text File | 1992-08-24 | 11KB | 299 lines

                FIFO.DOC

By: Matthew Dillon
            UUCP:    [e-mail]

        Version 3.2


    (1) INSTALLATION

    To Install the system you must install both FIFO-HANDLER and
    FIFO.LIBRARY.

    1> lharc -r -x -a x fifo3.lzh
    1> cd fifolib
    1> Copy l/fifo-handler l:
    1> Copy libs/fifo.library libs:

    THERE IS NO MOUNTLIST OR MOUNT FOR FIFO: ... To start the handler
    and make FIFO: available to programs, you must RUN it from your
    startup-sequence.  Generally the easiest way to do this is to
    include the following line:

    run <nil: >nil: l:fifo-handler

    IF YOU HAVE A FIFO: ENTRY IN YOUR MOUNTLIST, PLEASE DELETE IT TO
    PREVENT ACCIDENTLY TRYING TO MOUNT IT.

    (2) SIMPLE EXAMPLE TO GET YOU STARTED

    This is a simple example to get you started.  Please refer to
    section (3) below for a description of the options.

    1> type fifo:r
    1> run type s:startup-sequence >fifo:wmKe

    This particular examples requires that the reader be started first
    (due to the 'K' flag in the writer) but also allows you to ^C the
    reader (the first type command) without locking up the writer.

    (3) USAGE FOR FIFO:

    FIFO: is like PIPE: but is based on fifo.library rather than its
    own implementation.  Full master/slave support exists.    Since FIFO:
    uses fifo.library, programs that require non-blocking IO capability
    can access one side of a FIFO: connection via the fifo.library
    instead of FIFO:

    The implementation of FIFO: and fifo.library is a billion times
    better than that for my original PIPE: handler.

    The primary difference with FIFO: is that it is based on a
    MASTER-SLAVE connection.  Two MASTER-SLAVE connections going in
    opposite directions yields a full-duplex connection.  When using
    FIFO: to direct one program's output to another's input you must
    explicitly specify one of the FIFO:'s to be the master and the
    other the slave, as well as specify read & write flags.  The
    general format for accessing the FIFO: handler is as follows:

        FIFO:<name>/<flags>

    <name>:    a valid fifo name

    name may be any combination of alpha numerics up to 64 chars long,
    and is case sensitive.    FIFO: will append either "_m" or "_s" to
    the name it supplies to fifo.library depending on whether master
    mode or slave mode is selected.

    <flags>:    a valid combination of flags

    r   open for read.  Allows you to read from this fifo.

    w   open for write.  Allows you to write to this fifo

    rw  open for read & write (full duplex).  This opens a
        full duplex connection, generally useful only in
        remote-shell applications.

    c   open in cooked mode - must be specified on one side only,
        usually the slave side.  Any data received by the slave
        side is cooked before continuing on to the slave.  This allows
        the slave side, usually a shell and/or program, to change
        between cooked and raw mode with the standard SCREEN_MODE
        packet.

    e   EOF mode (when combined with 'w').  When this file handle
        is closed, an EOF will be sent to the other side.

        If not specified, you can cause several programs to 'append'
        their output onto a single FIFO all of which is read by a
        single program.  This can be useful in log-recorder
        applications, for example.

        Specifying the 'e' flag generates an EOF after the last byte
        of data is written to the FIFO and the writer closes it.  A
        reader will read the data and then receive the EOF, generally
        terminating reader operations.

    k   KEEP mode.    If a writer opens a fifo, writes data, then
        closes the fifo before a reader has a chance to open the
        fifo, this flag prevents the data from being lost.

        If not specified, the data will be lost.  Generally you
        want to specify this flag.

    K   READER REQUIRED mode.  When specified, any Write() operation
        to a fifo for which there is no reader will FAIL.  This will
        prevent lockups from occuring when you use FIFO: to pipe
        several processes together and then ^C the last one.

        ** This can be an important option to use to prevent hung
           processes!!! **

    m   select master side (else slave).  For example, the master
        side writer "mw" is paired with the slave side reader "r":

            mw   -> r
            mr  <-    w
            mrw <-> rw

        When operating a pipe where you have a writer into the fifo
        and then a reader from the same fifo, one of the two must
        be a MASTER, with the 'm' flag specified, and the other side
        must be a SLAVE, with the 'm' flag NOT specified, as per
        the example in section (2).

    t   tee read.  Usually specified "rt" or "mrt" depending on what
        you want to monitor.  This option causes the read stream to
        be a copy of available read data such that it does NOT
        interfere with other readers.

        Otherwise this fifo will compete with other fifos for read
        data.  For a remote shell, tee operation is not desireable
        as a default but is useful to monitor the shell from an
        independant program.

        see the REMCLI example below.

    s   SHELL mode, creates a separate message port for the handle,
        allowing the shell & progams to find their STDERR handle.
        (i.e. the open-* packet works properly).

        WARNING: use of this option increases overhead in the FIFO:
        device and is generally required to be specified for the slave
        side of a shell (i.e. newshell fifo:name/rwkecs)

        see the REMCLI example below.

    C   Send ^C to all (slaves or masters)
    D   Send ^D to all (slaves or masters)
    E   Send ^E to all (slaves or masters)
    F   Send ^F to all (slaves or masters)

        You can send one or more signal to all the slaves (or masters
        if 'm' is also included) using these flags.  note that it is
        not necessary to open a file handle to so, specifying a
        string like this:

        "FIFO:fubar/C"

        would result in sending a ^C to all fubar slaves even though
        the Open() fails due to the lack of a 'r' or 'w' in the
        specification.

             SEE REMCLI.C FOR EXAMPLE IMPLEMENTATION
             OF COOKED MODE AND SIGNALS.


    (4) TECHNICAL, INTERACTION BETWEEN FIFO: and FIFO.LIBRARY

                   LINKED FIFOS

    FIFO: provides a full duplex connection using TWO fifo.library FIFOS.
    Openning a fifo in master mode verses slave mode determines which
    names are used for reading and writing.  You should note that when
    a FIFO: handle is openned for both read and write, reading from the
    handle actually accesses a different physical fifo than writing to
    the handle.  Openning a FIFO: for only one direction ('r' *or* 'w')
    results in a half duplex connection.  It is important to properly
    specify the rw modes for the fifo.

         FIFO: device             fifo.library

    Open("FIFO:junk/w", 1005);              junk_s
    Open("FIFO:junk/r", 1005);              junk_m
    Open("FIFO:junk/rw",1005);              junk_s (w), junk_m (r)

    Open("FIFO:junk/wm", 1005);             junk_m
    Open("FIFO:junk/rm", 1005);             junk_s
    Open("FIFO:junk/rwm", 1005);            junk_m (w), junk_s (r)

    (5) REMOTE SHELL APPLICATIONS

    It is extremely easy to set up a fifo to interface a program with a
    remote shell.  The FIFO: fully supports remote shells including the
    ability to propogate ^C through ^F and handle stderr ("*").

    Not only that, but programs which need to be able to access the
    master side of a shell in a non-blocking fashion may access the
    master side directly through FIFO.LIBRARY calls.  See FIFOLIB.DOC
    for the function call list, see REMCLI.C for a working example.

    1> NewShell FIFO:name/rwkecs
    1> run remcli name

    Generally the shell is run off the slave side and the controlling
    program is run off the master side.  The side that runs the shell
    MUST specify the 's' option, as shown above.  Here is a description
    of the flags used in the NewShell line:

    rw  full duplex connection.  shell 'reads' from the master and
        'writes' results back to the msater.

    k   if slave side is started up first, as in the above example, any
        writes it does will NOT be lost.  Not really required since the
        slave side shell does not endcli itself.

    e   when slave side closes the handle, an EOF will be sent to
        the master side.

    c   run slave side in COOKED mode.  FIFO: will do command line
        editing on any data sent to the slave side.  You do not specify
        COOKED mode for the master side.  I repeat, do NOT specify
        cooked mode for the master side.  (you can't in the above
        example since the master is the 'remcli' program.

        note that in COOKED mode, FIFO: echo's characters received on
        the slave side back to the master, just like the console
        device.

    s   SHELL support, required on the slave specification when run
        from NewShell, causes the handle to get its own message port.
        (required to support Open("*", ...);

    NOTE:  YOU CAN RUN 'remcli name' MULTIPLE TIMES SIMULTANIOUSLY
    USING THE SAME FIFO NAME.  All remcli's talking to the same shell
    will get all output from the shell and additionally be able to
    issue commands.  This can be extremely useful as a monitoring tool.

        1> run remcli name
        1> run remcli name

    You can also capture all shell interaction with this:

        1> copy FIFO:name/rmt t:capture

    The 't' (TEE) specification is required to ensure you do not screw
    up any other readers.  There is no limit on the number of 'readers'
    monitoring a named fifo.  The RemCLI program uses the fifo.library
    to access the master side and thus TEEs automatically.

    If RemCLI tries to talk to a fifo that does not exist, it will
    'freeze' until the slave side does exist.  Meaning you can run
    RemCLI before you start up the shell.

    CLOSING THE REMCLI WINDOW DOES NOT END THE SHELL.  You must type
    'endcli' or 'endshell' to cause it to exit.  On the otherhand,
    closing the remcli window and then reopenning will yield the
    previous shell (which never exited).


                PIPEING

    You can use the FIFO: device to pipe output from one program to the
    input of another.  Note that you want to be sure to use the 'k' flag
    in case the program generating the output generates only a little (and
    is able to exit before you have a chance to start the reader).  You
    also want to use the 'e' (EOF) option or the reader will not receive
    an EOF, and you must make one side a master.

    1> type s:startup-sequence >FIFO:xx/wkme
    1> type FIFO:xx/r

    If you do not specify the 'e' EOF option then you can run multiple
    program's output through the pipe sequentially, specifying the eof
    option only for the last one.

    WARNING:    If you ^C the reader before it gets the EOF and exits
    on its own, and if the writer is still writing, the writer will
    freeze up when the fifo becomes full (requiring a reader to unfreeze
    it).  Additionally, if the 'k' option is not used, even if the writer
    does not freeze up there may be unwanted data left in the fifo even
    though nobody is referencing it.

    To safely recover from a broken reader, the program controlling the
    pipe must do the following steps:

    (1) break the writer if it has not exited (but it may be frozen,
        so...)

    (2) open a reader /r and a writer /wme, then immediately close
        the writer.

    (3) read from the reader until EOF.  Even if the original writer
        had already exited, the fact that you open and close a dummy
        one will regenerate the EOF.