Subject: Re: [boost] [lockfree::fifo] Review
From: Chris M. Thomasson (cristom_at_[hidden])
Date: 2010-01-20 01:42:50
"Andy Venikov" <avenikov_at_[hidden]> wrote in message
news:hfrs5q$anq$1_at_ger.gmane.org...
> Helge Bahmann wrote:
>>
>> There are valid uses for CAS with and without various types of barriers.
>> See the explicit memory_order specification in my atomic operations
>> library.
>
> So, CAS by itself doesn't imply anything, it's all about how you call it,
> right?
Humm, kind of. CAS on certain architectures actually implies quite a bit
(e.g., `LOCK' prefix on x86-32/64). However, since this is on a Boost Forum
I should probably be thinking abstract, in the sense of creating highly
portable algorithms in order to help make portions of the Boost libraries
expansive programming experience easier, so to speak; right?
;^)
Therefore, CAS is an atomic RMW with absolutely no effect on memory
visibility. However, I think that the return value from failed CAS to an
address A can be thought of as a "load". On the flip side, a successful CAS
on address B is basically a "store" in the sense of the successful RMW
portion of the CAS itself. The "load" from A can rise above the "store" to
B. CAS is irrelevant here and an external memory barrier operation might
need to be executed after the store to B in order to ensure that it is
"fully rendered into visible memory" _before_ the load from A is
"committed".