futex_wait_bitset(9)

✨ futex_wait_bitset(9) ✨

okay so bestie, quick vibe check: this is a page from the Kernel API Manual, and it's about futex_wait_bitset — the futex wait that's picky about which bits it wakes up for. no cap, it's giving "i'll block, but only for the specific bits i care about" 💅

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🌸 NAME 🌸

futex_wait_bitset — block on uaddr with bitset

like literally that's the whole name section, she's concise, she's iconic, we love her 🎀

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🦋 SYNOPSIS 🦋

int futex_wait_bitset (futex_t *uaddr , futex_t val , struct timespec
*timeout , u_int32_t bitset , int opflags );

(yeah the wrap happened mid-declaration up there, that's just how the original rolled, and we're keeping it EXACTLY as-is, fr fr 🫶)

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💜 ARGUMENTS 💜

okay so this is the part where the manpage kind of left us on read 😭 — most of these are literally marked -- undescribed -- in the source. i'm not gonna invent lore that isn't there, so here's the honest rundown:

• uaddr — -- undescribed -- 🙈 (the address you're futex-ing on, obviously, but the page itself says nothing, so neither do i)
• val — -- undescribed -- 💀
• timeout — -- undescribed -- ⌛ (it's a struct timespec *, do with that what you will)
• bitset — bitset to be used with futex_wake_bitset ⭐ — this is the one argument the page actually bothers to describe, and it's the whole point of the function, so like... main character energy honestly 👑
• opflags — -- undescribed -- 🫠

bestie, real talk: if you need the real semantics of uaddr, val, timeout and opflags, the manpage is not gonna hand them to you. check the kernel source and the selftest header below. i'm not out here guessing at kernel behaviour, that's not the move 💅

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🌈 SEE ALSO 🌈

• Kernel file ./tools/testing/selftests/futex/include/futextest.h 📁 — yes, that's the actual path, go look, iykyk
• futex(9)
• futex_wait(9)
• futex_wake(9)
• futex_wake_bitset(9)
• futex_lock_pi(9)
• futex_unlock_pi(9)
• futex_wake_op(9)
• futex_requeue(9)
• futex_cmp_requeue(9)
• futex_wait_requeue_pi(9)
• futex_cmp_requeue_pi(9)
• futex_cmpxchg(9)
• futex_dec(9)
• futex_inc(9)
• futex_set(9)

like, that's the whole futex friend group right there and they all showed up to the party 🔥

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that's the page, bestie! mwah 💋

source/version: ./tools/testing/selftests/fute... — yeah it's truncated in the footer, that's canon, we don't fix it 🎀

dated October 2026 — future girl summer ✨ see u in the next section, ily, bye! 🌸🦋💖