Subj : Re: Memory visibility and MS Interlocked instructions
To   : comp.programming.threads
From : Joe Seigh
Date : Fri Aug 26 2005 11:30 am

Alexander Terekhov wrote:
> Joe Seigh wrote: ...
> 
> <quote sources=tremblant.pdf>
> 
> 1.1 Atomics library approach
> 
> We have been discussing a library design in which primitives atomically 
> read and/or update a memory location, and may optionally provide some 
> memory ordering guarantees.
> 
> Nearly all lock-free algorithms require both atomic, i.e. indivisible, 
> operations on certain pieces of data, as well as a mechanism for 
> specifying ordering constraints. Allowing them to be combined in a 
> single operation (as opposed to providing separate atomic operations 
> and “memory barriers”) makes it possible to cleanly and precisely 
> express the programmer’s intent, avoids some unnecessary constraints 
> on particularly compiler reordering, and makes it easy to take 
> advantage of hardware primitives that often combine them.
> 
> [...]
> 
> On the vast majority of existing X86 processors, the “load” and “load 
> with acquire ordering semantics” primitives could use the same hardware 
> implementation, and would merely impose different compiler constraints. 
> Other processor architectures are split as to whether they require 
> separate implementations. The same applies to “store” and “store with 
> release semantics”.
> 
> We expect that in the final version of the library, operations such as 
> load and store will be parameterized in some form with an ordering 
> constraint
> 
> </quote>

You're talking about atomic<T>.  Memory barriers are an implementation
detail, not part of the semantics.  Unless of course you don't know
know to specify semantics with specifying an implementation.  But it's
not a good idea to conflate one with the other.


> 
> Why don't you simply spend your weekend studying the archives, Joe.
> 
> jupiter.robustserver.com/pipermail/cpp-threads_decadentplace.org.uk
> 

Why can't you directly answer specific questions like what is meant
by bidirectional and unidirectional?  Instead you blindside the
discussions with pirate talk semantics which nobody has a clue what
you're talking about.


-- 
Joe Seigh

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

.