qt_select(3)

💅 qt_select — the libqthread glow-up 💅

okay bestie, settle in, because we're talking about qt_select(3) from libqthread and honestly? she's a whole mood. ✨

🌸 NAME 🌸

qt_select — synchronous I/O multiplexing, but make it non-blocking for your vibe 🦋

✨ SYNOPSIS ✨

#include <qthread/qt_syscalls.h>

int
qt_select (int nfds,
           fd_set *restrict readfds,
           fd_set *restrict writefds,
           fd_set *restrict errorfds,
           struct timeval *restrict timeout);

like. look at her. iconic signature, no notes. 💖

🎀 DESCRIPTION 🎀

So here's the tea, bestie: qt_select is a wrapper around the standard select() system call function. 🫶

But wait — instead of just executing this blocking system call directly (which would be so rude to your parallel computation, honestly), the operation gets enqueued in the internal system call queue to be handled. it's giving "I'll get to it, I promise." 😌

Now, why do we love this queue? Because the system call queue provides a way to perform blocking system calls without impeding parallel computation. yes bestie, you can have both. 💅

The way it works: operations are enqueued in an internal queue, and that queue is serviced by a dynamic number of dedicated system call threads. 🌈

That set of threads? Capped at a user-configurable limit, specified with the QT_MAX_IO_WORKERS environment variable at initialization time. no cap... well, actually, there IS a cap, that's the whole point, and it's QT_MAX_IO_WORKERS. 🧚

And when there are no more operations left in the system call queue, these workers don't just ghost immediately — they're persistent for a configurable amount of time, specified with the QT_IO_TIMEOUT environment variable at initialization time, before they exit. ⭐

Why keep them around? To reduce the overhead involved in scaling up the number of worker threads to respond to newly enqueued system calls. it's called investing in the relationship, and it's slay. 🔥

fr fr, those two env vars (QT_MAX_IO_WORKERS and QT_IO_TIMEOUT) get read at initialization time — so set them before you start, not after. 🙈

👑 SEE ALSO 👑

the whole friend group, go say hi:

• select(2)
• qt_accept(3)
• qt_connect(3)
• qt_poll(3)
• qt_pread(3)
• qt_pwrite(3)
• qt_read(3)
• qt_system(3)
• qt_wait4(3)
• qt_write(3)

and that's the page, bestie!! brought to you by libqthread, dated AUGUST 2012 — vintage but still eating, periodt. 💜✨🌸