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From: jseigh <jseigh_es00@xemaps.com>
Newsgroups: comp.lang.c++
Subject: Re: Futex Stack Test...
Date: Thu, 8 May 2025 18:46:48 -0400
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On 5/3/25 21:57, Chris M. Thomasson wrote:
> On 5/3/2025 12:58 PM, Chris M. Thomasson wrote:
>> On 5/3/2025 11:19 AM, Bonita Montero wrote:
>>> Am 03.05.2025 um 20:02 schrieb Chris M. Thomasson:
>>>
>>>> Now, its fun to be able to get a lock-free stack with only single 
>>>> word exchange and cas, and have the ability to use it with a futex 
>>>> to allow one to wait on empty conditions.
>>>
>>> Is a lock-free stack with a single word CAS really possible without an
>>> ABA-problem ?
>>
>> Will get back to you. Need to run a bunch of errands. If you omit 
>> single item pop, yup. It's also possible to get rid of the cas in push.
> 
> The ABA problem _and_ memory issue is only there in on the single node 
> pop for a lock-free stack. If you just whack it with a nullptr aka flush 
> _all_ nodes, then you are all right and ready to roll.
> 
> Actually, IBM had/has a nice write up of it in an appendix for the 
> principles of operations iirc. I think it might of been in appendix 40 
> ish or something. God it's been a while since I read that Bonita. Then 
> they have a rather nifty PLO, or perform locked operation, again iirc...
> 
> The futex is fun to use because it allows one to wait on an empty 
> condition...
> 
> Actually, I remember Joe Seigh taking all the nodes in an exchange, 
> reversing them, and BAM, its FIFO. ;^)
> 

Probably for a MPSC queue.  I don't the FIFO semantics would hold up
very well for MPMC queue.

Joe Seigh