lab 18 - mux

     lab 18 - mux

     Much of my recent reading has led me back to
     various implementations of a multiplexer. This is
     an important and powerful abstraction and I want
     to understand it better. I know very little about
     it now. I'd like to implement one in limbo, for
     example to multiplex the link between sam and
     samterm as suggested in the protium paper. Hence
     my interest in sam in the earlier lab.

     Here is a some of the things I've been reading
     recently about multiplexers. See if you see a
     pattern. J. Hickey's Master thesis at MIT
     implements mux for plan9 which puts a 9p
     multiplexer into user space and provides
     asynchonous IO for user threads.

     Search 9fans for multiplexing where there is some
     interesting discussion on the use of multiplexers
     in plan9.

     For example, an idea by rog and russ's response

     And futher proposals by russ proposal for mux, 
     local 9p multiplexing and remote 9p multiplexing.

     See also an implementation of a generic rpc
     multiplexer, libmux, in plan9port

     The various window systems by Rob Pike, mux, 8½,
     and rio are multiplexers for their environment,
     the screen, mouse and keyboard.

     The spree game engine is a multiplexer at the
     application leve for the object hierarchy managed
     by the server.

     And in inferno /emu/port/devmnt.c is the
     multiplexer for 9p.

     In the original exokernel paper the authors argued
     the principal function of an operating system is
     to multiplex access to hardware, and should do
     nothing else. Multiplexers are vital to providing
     9p service and in protium the authors argue they
     are a vital piece of infrastructure for
     distributed applications. 

     In summary, this is something I need to learn more
     about. I'll proceed in these labs with studying
     the code to libmux and devmnt and try to implement
     the mux for the sam session.



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