NetNews Usenet Archive 1992 #30/NN_1992_30.iso/spool/comp/lang/cplus/18162

Text File | 1992-12-18 | 2.6 KB | 103 lines

Newsgroups: comp.lang.c++
Path: sparky!uunet!uunet.ca!ohrd!twriter
From: [e-mail] (Timothy Writer)
Subject: Re: Give me safe C++
Message-ID: <[e-mail]>
Reply-To: [e-mail]
Organization: "Ontario Hydro - Research Division"
References: <[e-mail]> <[e-mail]> <[e-mail]> <[e-mail]>
Date: Thu, 17 Dec 92 23:55:44 GMT
Lines: 91

[e-mail] (John MAX Skaller) writes:

>In article <[e-mail]> [e-mail] writes:

> [stuff deleted]

>    Next, I feel NO language has addressed the concept
>of coroutines (except possibly Simula?). C provides
>no simple exchange of control mechanism, although one
>has to admit they can be emulated using objects in C++.
>Yet many machines provide this facility, usually via
>some exchange and link instruction.

There was (is) a language called Concurrent Euclid which was invented at
the University of Toronto some years ago.  In my opinion, it addressed
the problem of concurrency (coroutines) quite effectively.  Euclid is
based on Turing, another University of Toronto language with strong
similarities to Pascal.  To Turing, Euclid added monitors and processes.
A process is simply a coroutine.  Monitors encapsulate critical data and
the procedures for manipulating them.  As only one procedure is aloud to
execute "in" a monitor, critical data is prevented from being
simultaneously accessed by multiple procedures.

Here is a very silly example.  I forget much of the syntax but it
illustractes the basic idea.

counter : Monitor

    var count : integer = 0

    procedure up()
    begin
        count = count + 1
    end

    procedure down()
    begin
        count = count - 1
    end

    precedure print()
    begin
        put(count)
    end

end Monitor

process up()
begin
    counter.up
    counter.print
end

process down()
begin
    counter.down
    counter.print
end

When the program starts up it immediately creates two processes
(coroutines) up and down.  The output might look something like this.

1
2
3
2
3
4
3
2
1
0
-1
0
...

Euclid also provides a means of synchronizing processes using signals
and conditions although I don't remember enough to describe it.

Although there are strong similarities between Euclid and Pascal,
Euclid is quite flexible.  In fact, I believe the same team that
implemented Euclid also built an implementation of UNIX, called TUNIS,
written entirley in Euclid.

Tim

--
Tim Writer                 phone:  [phone] ext. 6990
Ontario Hydro Research Division         fax:    [phone]
Toronto, Ontario             e-mail: [e-mail]
CANADA