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From: COS99284@UFRJ.BITNET (Luiz Felipe Perrone)
Newsgroups: comp.sys.transputer
Subject: Anarchic protocol ANY (occam2)
Message-ID: <9105152020.AA15174@theory.TN.CORNELL.EDU>
Date: 15 May 91 21:04:29 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 67
X-Unparsable-Date: Wed, 15 May 91 16:39:07 BRA

Dear netters,

  I have tried to use channels of protocol ANY in a very particular
situation and my results were very strange. I use ANY channels so
that one process can send various items of different types of data
to another process that will route the message and save one copy of it.
This latter process must see this message as an array of bytes and
forward it to the apropriate receiver as another array of bytes. Upon
receiving this message the receiver would break the array of bytes into
pieces corresponding to the same types sent by the first process.

  In occam part of this would correspond to (sorry, I can't use square
brackets in my terminal, I'll use parenthesis instead) the following code:
  Obs: the channel is global and declared as CHAN OF ANY; all messages
       are made of a header and a text of variable size

  Process 1 :
      REAL32 r:
      INT i, s, h1, h2:
      BOOL b:
      REAL64 x:
      SEQ
        r := 1.5 (REAL32)
        i := 1
        b := TRUE
        x := 3.1516 (REAL64)
        s :=17 -- size of message text in bytes
        h1, h2 := 0, 0
        to.p2 ! h1; h2; s; r; i; b; x

  Process 2:
      INT h1, h2, i, s:
      (100)BYTE buffer:
      SEQ
        to.p2 ? h1; h2; s::buffer


  Placing STOPs here and there I have observed that Process 1 finishes and
so it sends the message successfully. But what I'm trying to explain is why
Process 2 never finishes. I have some wild guesses such as: the code the
compiler generates for the input command in 2, is not appropriate to receive
the message text (s::buffer) because the channel to.p2 was declared as CHAN
OF ANY and not CHAN OF INT; INT; INT::()INT. Another one is that I may be
experiencing some alignment problem due to retyping conversions.

  If someone knows why this happens or how I could send one message of varying
length with any number of items of any type to a process that will see this
message as a well defined header plus a text defined as an array of bytes
of varying length, please let me know as soon as possible.

  I'm using this in the project of simulation kernel and I have to provide
an elegant, flexible and easy to use interface between the simulator and
the user's logical processes.

  Thank you all.

------------------------------------------------------------------------
Luiz Felipe Perrone
MSc student - COPPE - Dept. of Systems Engineering and Computer Science
Universidade Federal do Rio de Janeiro - Brazil
E-mail: COS99284@UFRJ (BITNET)
Mailing address:  Rua Senador Vergueiro 157/305
                  Flamengo - Rio de Janeiro, RJ - Brazil
                  CEP 22230

Phone number: (55)-(21)-5519063
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