pthread_sigqueue(3)

✨ pthread_sigqueue(3) ✨

okay bestie, so this one lives in the Library Functions Manual and it's a libc-adjacent baddie — let's get into it 💖

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🌸 NAME 🌸

pthread_sigqueue — queue a signal and data to a thread 👑

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🎀 LIBRARY 🎀

POSIX threads library — link it with -lpthread, and note that the actual library you're pulling in is libpthread. slay. 💅

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✨ SYNOPSIS ✨

#include <signal.h>
#include <pthread.h>

int pthread_sigqueue(pthread_t thread, int sig,
                     const union sigval value);

🦋 Feature Test Macro Requirements for glibc 🦋

(if you wanna know how this whole feature-test-macro thing works, go peek at feature_test_macros(7), bestie)

• pthread_sigqueue():
  • _GNU_SOURCE

ik ik, the macro gating is real. set _GNU_SOURCE or this function is just not gonna show up. no cap.

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💜 DESCRIPTION 💜

So pthread_sigqueue() basically does the same job as sigqueue(3)… except instead of yeeting a signal at a whole process, it sends the signal to a single thread in the same process as the calling thread. it's giving targeted delivery. 🎯

• thread — the ID of a thread that lives in the same process as the caller.
• sig — the signal you wanna send.
• value — the data that tags along with the signal. (head to sigqueue(3) if you want the full breakdown of that part 📬)

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🔥 RETURN VALUE 🔥

• On success, pthread_sigqueue() returns 0. 🫶
• On error, it returns an error number. (yes, an error number, not setting errno — that's just how the pthread girlies do it)

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💀 ERRORS 💀

• EAGAIN — the limit of signals that may be queued has been reached. like the queue said "no more room, babe" 😭 (see signal(7) for the deets)
• EINVAL — sig was invalid. nope, not that one.
• ENOSYS — pthread_sigqueue() is not supported on this system. she's simply not available here 🙈
• ESRCH — thread is not valid. that thread? doesn't exist. gone. 💀

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🌈 ATTRIBUTES 🌈

want the definition of the terms used in this section? go read attributes(7), i'll wait 💅

• pthread_sigqueue() — Thread safety attribute: MT-Safe ✨

so yeah, it's MT-Safe, we love a thread-safe icon.

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⭐ VERSIONS ⭐

Heads up: the glibc implementation of pthread_sigqueue() throws an error (EINVAL) if you try to send either of the real-time signals that the NPTL threading implementation uses internally. that's intentional, not a bug. nptl(7) has the details if you're curious 👀

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👑 STANDARDS 👑

GNU. that's it, that's the standard. periodt.

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🧚 HISTORY 🧚

glibc 2.11 — she's been around a minute 🎀

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🌟 SEE ALSO 🌟

• rt_tgsigqueueinfo(2)
• sigaction(2)
• pthread_sigmask(3)
• sigqueue(3)
• sigwait(3)
• pthreads(7)
• signal(7)

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and that's the whole page, bestie 🫶 this was Linux man-pages 6.20, dated 2026-02-08, and honestly? iconic. go queue a signal to a thread, you've earned it 💖✨