THR_SELF(2)

💅 THR_SELF(2) — the thr_self era

okay so bestie, welcome to thr_self from section 2 of the manual — the System Calls Manual, to be exact. yes we're in the syscall neighborhood, not the polite libc one. pull up a chair 🎀

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✨ NAME ✨

thr_self — returns the thread identifier for the calling thread. literally it's just "who am i, thread edition" and honestly? iconic self-discovery moment 💖

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📚 LIBRARY 📚

Standard C Library (libc, -lc)

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🫶 SYNOPSIS 🫶

#include <sys/thr.h>

int
thr_self(long *id);

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🌸 DESCRIPTION 🌸

so the thr_self() system call stores the system-wide thread identifier for the current kernel-scheduled thread into the variable that the argument id points at. that's it. that's the whole job. and she ate 💅

the thread identifier is an integer in the range from PID_MAX + 2 (100001) all the way up to INT_MAX. no cap, those are the real bounds.

it's guaranteed to be unique at any given time, for each running thread in the system — like every thread gets its own little name tag 🏷️✨. but — and this is the part where you go "oh 😭" — after the thread exits, that identifier may be reused. so don't go treating it like a forever-unique snowflake ID, bestie. reuse is real 🙈

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🔥 RETURN VALUES 🔥

• if it worked: thr_self() returns zero 🎉 slay
• if it didn't: -1 comes back, and errno is set to indicate the error 💀

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💀 ERRORS 💀

here's the whole error roster, and it's short so you can absolutely memorize it before chem class:

• [EFAULT] — the memory that the id argument points to is not valid. so like... it's a bad pointer. she's pointing at nothing. ghost memory 👻

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👑 SEE ALSO 👑

_umtx_op(2), thr_exit(2), thr_kill(2), thr_kill2(2), thr_new(2), thr_set_name(2), pthread_getthreadid_np(3), pthread_self(3)

(go read these next, the whole thread friend group is lowkey fascinating 🦋)

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🌈 STANDARDS 🌈

real talk: the thr_self() system call is non-standard. it's not some blessed POSIX-certified icon, it's a FreeBSD special 💅. it exists because the 1:1 Threading Library (libthr, -lthr) uses it to implement IEEE Std 1003.1-2001 (“POSIX.1”) pthread(3) functionality — i.e. she's the backstage crew making the main-character pthreads look effortless ✨

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🧚 HISTORY 🧚

the thr_self() system call first appeared in FreeBSD 5.2. throwback era fr fr 🎀

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warning bestie: [EFAULT] is the only error listed, so if your id pointer is garbage, that's what you're getting. keep that pointer valid and hydrated 🍓

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that's the whole page, you understood it perfectly, i'm obsessed with you 🫶💜

— from the Debian edition of this page, dated May 5, 2020, sourced straight from the System Calls Manual, mwah 💋⭐