/g/ - syscall of the day: semget/semop/semctl - Technology


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Anonymous
syscall of the day: semget/sem(...) 02/28/26(Sat)11:21:55 No.108262843

File: 1737780691839246.jpg (222 KB, 2048x2048)

syscall of the day: semget/semop/semctl Anonymous 02/28/26(Sat)11:21:55 No.108262843

previous: >>108252317
#define __NR_semget                64
#define __NR_semop                65
#define __NR_semctl                66
https://man7.org/linux/man-pages/man2/semget.2.html
https://man7.org/linux/man-pages/man2/semop.2.html
https://man7.org/linux/man-pages/man2/semctl.2.html

tl;dr:
semaphores, but worse!
https://man7.org/linux/man-pages/man7/sem_overview.7.html
to be clear, these syscalls are NOT posix semaphores. but the above link mentions them in the notes, and it should explain a bit more

i try to avoid any multi-threading primitives outside of the basic mutex and condition variable. i know that the others have their places, and there are definitely circumstances where they're far better suited to the task at hand, but they're also way less widely known and used. if you stick to just mutexes and cvs, it's a lot easier for anyone coming after you to read your code and know what the hell is going on.
what about you, anon? what's been your experience with multi-threading primitives? have you ever used semaphores before? if so, why?
bonus: https://en.wikipedia.org/wiki/Semaphore
are you familiar with where the term semaphore came from? most people are, but in case you aren't, give this article a read. it's pretty interesting

relevant resources:
man man
man syscalls
https://man7.org/linux/man-pages/
https://linux.die.net/man/
https://elixir.bootlin.com/linux/
https://elixir.bootlin.com/musl/
https://elixir.bootlin.com/glibc/

Anonymous
02/28/26(Sat)11:51:37 No.108262995

Anonymous 02/28/26(Sat)11:51:37 No.108262995

>are you familiar with where the term semaphore came from? most people are, but in case you aren't, give this article a read. it's pretty interesting
I only knew that semaphore was traffic light in Czech/Slovak, so I was familiar with the term before I knew about semaphores in computers, but I didn't know its actual origin.

>what about you, anon? what's been your experience with multi-threading primitives? have you ever used semaphores before? if so, why?
I read about them on the Osdev wiki when I was browsing through it, but I never got far enough with my hobby OS that they would have been of any use though. I never programmed anything with semaphores, and I doubt I will any time soon.

Also putting questions in the OP makes it easier to know what to respond with, so it's easier to have a conversation like this.

Anonymous
02/28/26(Sat)11:53:56 No.108263011

Anonymous 02/28/26(Sat)11:53:56 No.108263011

>>108262843
i'm gonna fuck your ass

Anonymous
02/28/26(Sat)12:00:42 No.108263045

Anonymous 02/28/26(Sat)12:00:42 No.108263045

File: 1767852603238574.png (236 KB, 736x820)

236 KB PNG

>>108263011
i'm mostly sex negative, i think

Anonymous
02/28/26(Sat)12:02:03 No.108263053

Anonymous 02/28/26(Sat)12:02:03 No.108263053

>what about you, anon? what's been your experience with multi-threading primitives? have you ever used semaphores before? if so, why?
I used semaphores when implementing blocking in a multiple-producer multiple-consumer queue. If a thread tries to pop an entry out of an empty queue, it runs sem_wait, and when a thread adds something to a queue, it checks to see if any threads are blocked on it, and then runs sem_post to wake them up. Those were posix semaphores though.
Nowadays I'd probably just use a futex instead, but it worked fine.

Anonymous
02/28/26(Sat)13:27:57 No.108263556

Anonymous 02/28/26(Sat)13:27:57 No.108263556

>you stick to just mutexes and cvs, it's a lot easier for anyone coming after you to read your code and know what the hell is going on.
As far as I understand it, the point of these semaphore apis isn't necessarily for thread synchronization but process synchronization.
So why does the OS only provide syscalls for semaphore, but not for mutex? You can trivially implement mutex in terms of semaphore operations, but I guess the other way around isn't as straightforward? I haven't really played this out my head.

Anonymous
02/28/26(Sat)14:00:08 No.108263760

Anonymous 02/28/26(Sat)14:00:08 No.108263760

she semgets me if you know what i mean

Anonymous
02/28/26(Sat)14:32:11 No.108263991

Anonymous 02/28/26(Sat)14:32:11 No.108263991

>>108263556
it does provide syscalls for mutexes

Anonymous
02/28/26(Sat)18:16:17 No.108265411

Anonymous 02/28/26(Sat)18:16:17 No.108265411

bampu

Anonymous
02/28/26(Sat)18:31:09 No.108265526

Anonymous 02/28/26(Sat)18:31:09 No.108265526

>>108263045
idc

Anonymous
02/28/26(Sat)18:32:23 No.108265536

Anonymous 02/28/26(Sat)18:32:23 No.108265536

mob face sexo

Anonymous
02/28/26(Sat)19:55:07 No.108266175

Anonymous 02/28/26(Sat)19:55:07 No.108266175

>>108265526
l-lewd....
>>108265536
you too honestly

Anonymous
02/28/26(Sat)20:32:28 No.108266486

Anonymous 02/28/26(Sat)20:32:28 No.108266486

semop is pomes backward
have you ever written a pome, OP

Anonymous
02/28/26(Sat)20:47:53 No.108266609

Anonymous 02/28/26(Sat)20:47:53 No.108266609

>>108266486
>a fruit consisting of a fleshy enlarged receptacle and a tough central core containing the seeds, e.g., an apple or pear
a fleshy enlarged receptacle......
i wrote poems as an angsty teen, yes

Anonymous
02/28/26(Sat)22:39:08 No.108267349

Anonymous 02/28/26(Sat)22:39:08 No.108267349

bampu 2

Anonymous
02/28/26(Sat)23:11:23 No.108267576

Anonymous 02/28/26(Sat)23:11:23 No.108267576

why does glibc mimic a lot of kernel syscalls? do they think they can do it better or is it a comparability question?

Anonymous
02/28/26(Sat)23:42:18 No.108267754

Anonymous 02/28/26(Sat)23:42:18 No.108267754

>>108267576
it (generally) doesn't mimic them, but just wraps them

Anonymous
03/01/26(Sun)00:56:12 No.108268062

Anonymous 03/01/26(Sun)00:56:12 No.108268062

>>108262843
>what's been your experience with multi-threading primitives?
linux futexes are pretty good

Anonymous
03/01/26(Sun)01:05:46 No.108268097

Anonymous 03/01/26(Sun)01:05:46 No.108268097

>>108262843
I wish I can draw like this.

Anonymous
03/01/26(Sun)01:08:25 No.108268106

Anonymous 03/01/26(Sun)01:08:25 No.108268106

>>108268097
just download stablediffusion

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