FUTEX_REQUEUE(2const)

💖 FUTEX_REQUEUE — it's giving "wake some besties, shuffle the rest" 💖

okay so bestie, this is a 2const page from the Linux man-pages situation, and it's all about the FUTEX_REQUEUE operation. Pull up a chair, grab a boba, we're doing kernel-adjacent lore 🧚✨

🌸 NAME 🌸

FUTEX_REQUEUE — wake some waiters, and requeue others 🫶

📚 LIBRARY 📚

Standard C library (libc, -lc) — the classic, no cap.

✨ SYNOPSIS ✨

#include <linux/futex.h>  /* Definition of FUTEX_* constants */
#include <sys/syscall.h>  /* Definition of SYS_* constants */
#include <unistd.h>

long syscall(SYS_futex, uint32_t *uaddr, FUTEX_REQUEUE,
             uint32_t val, uint32_t val2, uint32_t *uaddr2);

like yes, you're calling syscall() directly, main character energy fr fr. 👑

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🦋 DESCRIPTION 🦋

okay so here's the tea: this operation does the exact same task as FUTEX_CMP_REQUEUE(2const) — literally the same job, same vibes — except that the futex word isn't compared. that's it. that's the difference. no vibe check on the futex word, no comparison, we simply move different. 💅

🔥 RETURN VALUE 🔥

• on error bestie? it returns -1, and errno gets set to tell you what went wrong. rude but informative 😭
• on success, FUTEX_REQUEUE returns the number of waiters that were woken up. slay. those are your freshly-awakened besties ✨

💀 ERRORS 💀

first up: also see futex(2), that's the big lore page.

• EFAULT — uaddr2 didn't point to a valid user-space address. like, that address is not a real place, it's giving void 🫠
• EINVAL — uaddr2 doesn't point to a valid object — meaning the address is not four-byte-aligned. misaligned? not the vibe. nope.
• EINVAL — the kernel detected an inconsistency between the user-space state at uaddr and the kernel state — that is, it detected a waiter which waits in FUTEX_LOCK_PI(2const) or FUTEX_LOCK_PI2(2const) on uaddr. yes that's the same EINVAL, two whole reasons, we stay thorough 💜

🌈 STANDARDS 🌈

Linux. just Linux. iconic of it, honestly.

⭐ HISTORY ⭐

Linux 2.6.0 — an elder. a pioneer. we respect the ancestors 🎀

👀 SEE ALSO 👀

• futex(2)

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lowkey if you're here, you're already deep in the futex trenches, and honestly? obsessed. 🫶

and that's the whole page bestie!! this one's from Linux man-pages 6.20, dated 2025-05-30, and it's the FUTEX_REQUEUE(2const) page — periodt. 💖✨🌸