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From: casper@fwi.uva.nl (Casper H.S. Dik)
Newsgroups: comp.lang.ada
Subject: Re: Easily-Read C++?
Date: 11 Oct 1994 14:44:18 +0100
Organization: FWI, University of Amsterdam
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References: <1994Oct7.153254.29848@swlvx2.msd.ray.com>
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 <1994Oct11.090047.9190@sei.cmu.edu>
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Date: 1994-10-11T14:44:18+01:00
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firth@sei.cmu.edu (Robert Firth) writes:

>The C code I've seen is absolutely littered with this stuff. I am
>continually amazed that *anything* still works when people write
>true multitasking code in C.

Why?  The only think you need to take care of in C when writing
multi-threaded code is using proper (explicit) locking of global
data.  Most of the foo++ usages in C are of automatic variables.
Those aren't shared between threads or even function invocations
and consequently there is no problem with c++ kind of code.

However, when incrementing a global variable one should do something
like this:

	set_write_lock(foo_lock);
	foo++;
	unlock_write_lock(foo_lock);

The problem with C multi-threading is making the locking explicit.
You may also need to make such variable "volatile"  which is C-speak
for "can be modified behind my back".

Locking is also necessary for reading variables that are shared
between threads (and modified by some of those threads).

I really don't see what the difference between "foo = foo + 1"
or foo++ is in this context.

Casper