volatile (in comp.lang.c)

[Ray Dunn]

In article <1988May23.003847.1114 at utzoo.uucp> (Henry Spencer) writes:
 [quoting an article without attributing it]
>> ....  To get behaviour that is the same for all compilers, the 
>> variable v must be declared volatile.
>
>Unfortunately, this is not sufficient.  "Volatile" does not guarantee
>that operations are atomic.  It is entirely possible for x and/or y to
>contain trash because they caught the variable midway through the
>assignment.

Fortunately this is sufficient when the programmer understands what he is
programming, and chooses data types etc which will ensure atomicity, if that
is what he is trying to achieve.

Even in assembler, problems will result if a non-atomic instruction is used
in a semaphore mechanism.

All "volatile" gives in this shared memory context is a basic low level tool
that a careful programmer can use to sufficiently handle this class of
problems.  All the compiler need be aware of is that a reference to a
volatile variable must always generate a memory reference.

-- 
Ray Dunn.                      |   UUCP: ..!{philabs, mnetor}!micomvax!ray
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