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From: "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com>
Newsgroups: comp.arch
Subject: Re: MSI interrupts
Date: Fri, 28 Mar 2025 09:51:54 -0700
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On 3/28/2025 8:24 AM, MitchAlsup1 wrote:
> On Fri, 28 Mar 2025 2:53:57 +0000, Dan Cross wrote:
[...]
> 
> Generally when I write queue-code, I use a dummy Node front/rear
> such that the checks for Null are unnecessary (at the cost of
> following 1 more ->next or ->prev). That is Q->head and Q->tail
> are never NULL and when the queue is empty there is a Node which
> carries the fact the queue is empty (not using NULL as a pointer).
> 
> But that is just my style.

Actually, it's a fairly common practice to use a dummy node in 
lock/wait-free queues. For instance:

https://www.cs.rochester.edu/research/synchronization/pseudocode/queues.html

In fact, wrt the C++20 futex stack code I posted to this group uses a 
dummy address:

#define CT_WAIT ((ct_node*)0xDEADBEEF)

To define a wait state for the C++20 futex to use wrt avoiding 
slow-paths. However, this scares me a bit because if the user allocates 
a node that has that exact address, it will break the algorithm. So, I 
really should create a dummy node and use that for the wait condition. 
Have you seen that post "Futex Stack..."?