compare and swap operation

[Yang Zhang]

I am reading some lock-free shared data-structures currently and am
planning to implement some of them. They are mostly built on the atomic
CAS (compare and swap) operation. I am just wondering how can I use the
hardware CAS instruction? I googled for some time, but it seems there is
very little information on this. I am mainly using C++, pthread library
and the GNU g++ compiler and how can I use the hardware CAS instruction
on Intel/Linux, Sparc/Solaris, and MIPS/IRIX systems. Can someone
provide some examples or point me to the right place? Thanks in advance.

--Yang

[Steve Watt]

In article <WFL2f.10061$5l....@bignews6.bellsouth.net>,

If you are going to be doing lock-free programming, you will need
to understand that the primitives involved are not portable between
different CPU architectures.

For example, MIPS systems don't have CAS, but rather a
load-linked/conditional-store instruction pair. It's been long enough
since I touched a SPARC that I've now forgotten what synch primitives
are available there. You will need to concern yourself with what order
memory accesses become visible to other processors, and those details
change with each architecture (and often within implementations of an
architecture!).

You are entering an area that's surprisingly complex. Unless you have
compelling evidence that you need lock-free techniques, I would suggest
avoiding them at the application level, and using the primitives the
system provides.

If you plan on writing an API layer for your lock-free queues (or
whatever), there's a couple of other recent threads (pun not intended)
in this newsgroup that might get you started.
--
Steve Watt KD6GGD PP-ASEL-IA ICBM: 121W 56' 57.8" / 37N 20' 14.9"
Internet: steve @ Watt.COM Whois: SW32
Free time? There's no such thing. It just comes in varying prices...

[Sean Kelly]

Microsoft provides CAS-like functionality via its
InterlockedCompareExchange function. Another option is to write inline
assembler, though this is obviously nonstandard. I'm not aware of any
cross-platform APIs to do this, though I'm sure they must exist.

Sean

[Joe Seigh]

Check out the atomic_ops package here
http://www.hpl.hp.com/research/linux/qprof/

--
Joe Seigh

When you get lemons, you make lemonade.
When you get hardware, you make software.