THR_KILL(2)

💅 THR_KILL(2) — like, the thread-signalling girlies 💅

okay bestie, welcome to THR_KILL(2), the System Calls Manual page where we learn how to slide a signal into one specific thread instead of dumping it on the whole entire process. iykyk. 💌

---

✨ NAME ✨

thr_kill — send signal to thread 🎯

---

🫶 LIBRARY 🫶

Standard C Library (libc, -lc) — she's built in, no extra shopping required. 💖

---

🌸 SYNOPSIS 🌸

#include <sys/thr.h>

int
thr_kill(long id, int sig);

int
thr_kill2(pid_t pid, long id, int sig);

---

🦋 DESCRIPTION 🦋

so the thr_kill() and thr_kill2() system calls let you send a signal — the one you specify with the sig argument — to some threads in a process. not all of them. some. targeted. main character selectivity. ✨

quick vibe check on who's allowed to get signalled:

• with thr_kill(), the signalled threads are always limited to the current process. she stays home. no wandering. 🏠
• with thr_kill2(), the pid argument specifies the process whose threads you wanna signal. so you can go visit. 🌍

now, the id argument is the whole "which thread tho" situation:

• if id is equal to -1, all threads in the specified process are signalled — it's giving group chat blast 📢
• otherwise, only the thread with the thread identifier equal to the argument is signalled — it's giving DM 💌

and the sig argument defines the delivered signal. it must be a valid signal number or zero. yes, zero is a real option, and here's the tea: in that case no signal is actually sent, and the call is used to verify the liveness of the thread. basically a "u up?" text. 👀🫶

one more detail, don't skip it: the signal is delivered with siginfo si_code set to SI_LWP. 📎

---

🎀 RETURN VALUES 🎀

if successful, thr_kill() and thr_kill2() will return zero. otherwise -1 is returned, and errno is set to indicate the error. slay when it works, 😭 when it doesn't.

---

🔥 ERRORS 🔥

the thr_kill() and thr_kill2() operations return the following errors:

• [EINVAL] — the sig argument is not zero and does not specify a valid signal. 🚫
• [ESRCH] — the specified process or thread was not found. she's not here, babe. 💀

additionally, the thr_kill2() may return the following errors:

• [EPERM] — the current process does not have sufficient privilege to check existence or send a signal to the specified process. 🔒 nope, not allowed, no cap.

---

🌈 SEE ALSO 🌈

_umtx_op(2), kill(2), thr_exit(2), thr_new(2), thr_self(2), thr_set_name(2), pthread_kill(3), signal(3)

the whole friend group fr fr 🫂

---

👑 STANDARDS 👑

the thr_kill() and thr_kill2() system calls are non-standard — they're built diff, they don't follow the crowd 💅 — and are used by the 1:1 Threading Library (libthr, -lthr) to implement IEEE Std 1003.1-2001 ("POSIX.1") pthread(3) functionality. iconic behaviour, honestly. ⭐

---

⭐ HISTORY ⭐

the thr_kill() and thr_kill2() system calls first appeared in FreeBSD 5.2. she's been around. vintage. 🎀

---

ngl bestie, sig of zero is genuinely useful — it's the liveness check — but don't go thinking you can send just any number in there, EINVAL will humble you real quick. 🙈

---

that's the whole page!! mwah 💋 this was THR_KILL(2) from Debian, dated May 5, 2020 — go be iconic with your threads, ily, bye 🧚‍♀️💜