Re: mutexes, locks and so on...

[der Mouse <mouse%Rodents-Montreal.ORG@localhost>]

> Hadn't it been much nicer of we just had the mutex and lock
> abstraction, and left the whole implementation to each MD part?

Exactly.  Consider this hypothetical:

x86 does #define ATOMIC_OPS_USE_CAS and defines a CAS(); MI code
notices this and defines all the higher-level primitives (if that's not
too much of an oxymoron) in terms of CAS().

ppc, arm, all the arches sufficiently "modern" to have CAS, likewise.

Arches without a sufficiently general CAS[%] do not define
ATOMIC_OPS_USE_CAS and provides their own implementations of mutexes,
spinlocks, whatever.

That seems to me like a mostly sane way to do it.  If I can come up
with it in thirty seconds, it seems likely anyone capable of doing such
overhauls could come up with it.

Instead, all arches must implement a fully-general CAS.  Seems to me
like a lose.

[%] It occurs to me, the VAX's BBSSI and BBCCI _are_ CAS, just
restricted to a one-bit-wide operand (and with the data-to-swap-in
specified by choice of instruction rather than an operand).

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