Re: [Gm2] (no subject)

[Izo]

Abi Lover wrote:

> Hi everyone,
>
> I am new to this mailing list. I joined in order to ask a specific 
> question. Is anyone here an expert on C/C++ as well as on Modula-2? My 
> question requirtes a knowledge of both.
>
> In Modula-2 there are a couple of language constructs which enable you 
> set up several co-routines and make them run (or appear to 
> run)concurrently: they are NEWPROCES and TRANSFER. They are also very 
> useful to enable you to mimic some real life situations. Is there 
> anything equivalent to this in C or C++?

No. This is purely M2 specialty and especially PIM2 which introduced the 
feature. It is not really useful in real situations since there is no 
scheduler and none of the stuff intended to resolve some process 
interactions and synchronization. But it was a good starter back in the 
'70 and '80 when M2 was designed as real programming tool step derived 
from the Pascal and as such it was widely used in embedded systems of 
that time. Normally you had to rewrite the underlying Process code to be 
really useful - I did some realtime extensions on HD6303 and MC68332 
micros back at those times using rewritten and extended Process code.

All in all you can regard the Process module as the portable "multitask" 
level with all its limitations for demo and learning purposes.

> As far as I know there didn't used to be, but GCC has added many new 
> extensions to C and C++, and I don't know enough about them to know 
> whether this is included. If it is not, how would you implement such a 
> code in C or C++? 


Well, gcc has not added any extensions to the C/C++. What happened is 
the POSIX extensions on threads in both kernel and user space which 
resulted on 2 major libc changes in past few years which resulted to 
non-functionality and non-portability of some code which is another 
story and has nothing to do with the C/C++ language specification which 
by all means is inferior to the M2's. On Unices the original 
multitasking enviroment is multiprocessing, while threading was added 
lately. So be encouraged at this point to use the POSIX (unistd.h : 
fork(), execwhatever(); pthread library) and WIN32 process and thread 
functions depending on the system where you use either GM2 or C++.

> I have attached a small program which illustrates the use of this 
> construct on Modula-2. This code was written using the old JPI 
> TopSpeed Modula-2, running on DOS. It was written by our lecturer to 
> illustrate this principle more than 10 years ago, when I was taught M2 
> at colege for the first time. It is a simple program which draws three 
> boxes on the screen: in the first a star keeps moving back and forth, 
> in the second the text, "Have a nice day," is constantly scrolling, 
> and in the third you can enter text from the keyboard. All three 
> events appear to be hapenning at the same time. Suppose you wanted to 
> translate this code into C or C++, how would you do it? 

The best way is to use XDS-C compiler which will have to use the native 
M2 RTS (RunTimeSystem).

The next way is to get you a source of the GM2 or the GardensPoint M2 
Process module which are written in C or maybe even in assembly - thus 
you will get the insight into the real M2 Process happening.

> Thanks for your help

You're welcome !

I.