PTHREAD_RWLOCKATTR_SETKIND_NP(3)

✨ NAME ✨

okay bestie, gather round 💖 this is the manual page for pthread_rwlockattr_setkind_np, pthread_rwlockattr_getkind_np — and they're here to set/get the read-write lock kind of the thread read-write lock attribute object. that's it, that's the whole job. 💅

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📚 LIBRARY 📚

POSIX threads library — libpthread, -lpthread. yeah you gotta link it, no cap. 🔗

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🩷 SYNOPSIS 🩷

#include <pthread.h>

int pthread_rwlockattr_setkind_np(pthread_rwlockattr_t *attr,
                       int pref);
int pthread_rwlockattr_getkind_np(
                       const pthread_rwlockattr_t *restrict attr,
                       int *restrict pref);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

pthread_rwlockattr_setkind_np(), pthread_rwlockattr_getkind_np():
    _XOPEN_SOURCE >= 500 || _POSIX_C_SOURCE >= 200809L

bestie listen 😭 these macros are the bouncers at the club. no matching <italic>feature test macro</italic>, no entry, and the function literally doesn't exist for you. pls define them before you #include anything.

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🌸 DESCRIPTION 🌸

so pthread_rwlockattr_setkind_np() sets the "lock kind" attribute of the read-write lock attribute object referred to by attr to the value you put in pref. lowkey simple. ✨

the argument pref may be set to one of these three icons only 👑:

• PTHREAD_RWLOCK_PREFER_READER_NP — the default, the main character, the one you get if you say nothing 🎀. a thread may hold multiple read locks; that is, read locks are recursive. according to The Single Unix Specification, the behavior is unspecified when a reader tries to place a lock, and there is no write lock but writers are waiting 😬. giving preference to the reader, as is set by PTHREAD_RWLOCK_PREFER_READER_NP, implies that the reader will receive the requested lock, even if a writer is waiting. as long as there are readers, the writer will be starved. yes, starved. that writer is in the group chat typing and nobody's reading 💀.
• PTHREAD_RWLOCK_PREFER_WRITER_NP — this is intended as the write lock analog of PTHREAD_RWLOCK_PREFER_READER_NP. and now the plot twist: this is ignored by glibc 🙈 because the POSIX requirement to support recursive read locks would cause this option to create trivial deadlocks. so instead use PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP, which ensures the application developer will not take recursive read locks thus avoiding deadlocks. it's giving "we love you but we're not doing what you asked" fr fr.
• PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP — setting the lock kind to this avoids writer starvation as long as any read locking is not done in a recursive fashion. the one that actually eats. 🔥

and pthread_rwlockattr_getkind_np() returns the value of the lock kind attribute of the read-write lock attribute object referred to by attr in the pointer pref. it reads it back and hands it to you, no drama. 🫶

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⭐ RETURN VALUE ⭐

on success, these functions return 0. iconic. periodt.

given valid pointer arguments, pthread_rwlockattr_getkind_np() always succeeds. it literally cannot fail on you, bestie, it's that reliable 🧚.

on error, pthread_rwlockattr_setkind_np() returns a nonzero error number. so like, check it, don't be out here ignoring return values, that's not the vibe. 😭

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💀 ERRORS 💀

• EINVAL — pref specifies an unsupported value. you made up a lock kind, girl. it is not real. it is not valid. go pick one of the three. 🙈

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🌈 STANDARDS 🌈

GNU. hence the suffix _np in the names — "(nonportable)". it's nonportable on purpose, that's its whole brand 💅. don't expect this energy to travel.

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💜 HISTORY 💜

glibc 2.1. ancient. historic. still here, still slaying. 👑

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🦋 SEE ALSO 🦋

• pthreads(7)

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and that's the whole page bestie!! 💖✨ this legendary lore comes to you from Linux man-pages 6.20, dated 2026-02-08 — the pthread_rw..._setkind_np(3) era 🎀🫶 go forth and set your lock kinds responsibly, mwah 💅