Re: best approach for multithreading (?)

On 12/8/2024 1:31 AM, Kaz Kylheku wrote:

On 2024-12-08, Chris M. Thomasson <chris.m.thomasson.1@gmail.com> wrote:

On 12/7/2024 7:49 PM, Kaz Kylheku wrote:

On 2024-12-07, James Kuyper <jameskuyper@alumni.caltech.edu> wrote:

My words above not-withstanding, I am not in any sense an expert on any
kind of threading, nor of Windows. What does POSIX require of threads
with regards to signals?

>
Off the top of my head, the highlights:
>
- threads have their own signal masks, inherited from the creator which
    calls pthtead_create.
- signal masks can be manipulated so that a given signal will be
    handled in the context of a desired thread.
- sigwait (and several other functions) can be used by a thread to
    wait for one or more signals, allowing signals to be process
    synchronously, somewhat like message passing.
>

>
Semaphores are sig safe, so to speak. It's been a while:
>
https://www.man7.org/linux/man-pages/man3/sem_post.3.html
>
should be sig safe? Or, am I wrong here Kaz?

 Yes; just not sem_wait. The obvious idea there is that a signal handler
is like an interrupt service top half, and those must be able to bang
semaphores, to wake up something waiting in the bottom half code.
 

Exactly. Actually, I remember a while back (several decades ago) when I was experimenting with lock/wait-free algorithms in sig handlers. They worked fine. Some of the algorithms would allow one to conditionally wait (futex, eventcount, ect...) say wait on a lock-free stack empty condition. So those could not be used. However, the "try" versions of them would work fine. :^)