aio_init(3)

✨ aio_init(3) ✨

okay bestie, we're in the Library Functions Manual today and the vibe is: you wanna be the main character of asynchronous I/O 💅 this is all about aio_init — asynchronous I/O initialization, no cap.

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🦋 LIBRARY 🦋

Real-time library (librt, link it with -lrt) — yeah she lives in librt, don't forget the flag or the linker will simply not know her 💀

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🌸 SYNOPSIS 🌸

#define _GNU_SOURCE         /* See feature_test_macros(7) */
#include <aio.h>

void aio_init(const struct aioinit *init);

like, you gotta define _GNU_SOURCE first (peep feature_test_macros(7) for the lore on why), then pull in <aio.h>, then boom — one function, one pointer, that's the whole mood 🫶

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🎀 DESCRIPTION 🎀

So aio_init() is GNU-specific — she's not POSIX, she's glibc's own little baby. What she does is let you, the caller, hand over some tuning hints to the glibc POSIX AIO implementation. It's giving "let me customize my experience" ✨

Using this function is optional, but — and this is the important part, bestie — to actually be effective she must be called before you use any other function in the POSIX AIO API. Like, she's the pregame, not the afterparty. Call her late and she's just sitting there, useless, not slaying 😭

The tuning info goes in the buffer that the init argument points to. That buffer is a structure that looks exactly like this:

struct aioinit {
    int aio_threads;    /* Maximum number of threads */
    int aio_num;        /* Number of expected simultaneous
                           requests */
    int aio_locks;      /* Not used */
    int aio_usedba;     /* Not used */
    int aio_debug;      /* Not used */
    int aio_numusers;   /* Not used */
    int aio_idle_time;  /* Number of seconds before idle thread
                           terminates (since glibc 2.2) */
    int aio_reserved;
};

notice how half of those fields are just sitting there with "Not used" energy? they're the wallflowers of the struct, we love them anyway 🙈

Here's the tea on the fields that actually do something in the aioinit structure:

• aio_threads — this one sets the max number of worker threads the implementation is allowed to use. If your outstanding I/O operations go over that limit, the extra ones just get queued up and wait politely until a worker thread frees up (very demure, very mindful 🧚). If you specify anything less than 1, the value 1 gets used instead. The default is 20.
• aio_num — this should be the max number of simultaneous I/O requests you expect to enqueue. If you give it anything less than 32, it gets rounded up to 32. The default is 64.
• aio_idle_time — this is the amount of time, in seconds, that a worker thread should wait for more requests before it terminates — and this is after it already finished a previous request. The default is 1.

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👑 STANDARDS 👑

GNU. that's it. that's the standard. she's a GNU girlie 🎀

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⭐ HISTORY ⭐

glibc 2.1 — she's been around a minute, lowkey iconic for it 💜

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🌈 SEE ALSO 🌈

• aio(7)

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and that's the whole page, bestie!! go forth and initialize your async I/O ✨ this was aio_init(3) from Linux man-pages 6.20, dated 2026-02-08 — slay, periodt, bye 🫶💖