qt_poll(3)

💅 qt_poll — bestie's guide to synchronous I/O multiplexing ✨

okay so this is qt_poll, from the libqthread manual (section 3, the library girlies 🫶). she's giving "poll but make it non-blocking-for-your-other-threads" and honestly? iconic.

✨ SYNOPSIS ✨

#include <qthread/qt_syscalls.h>

int
qt_poll (struct pollfd fds[], nfds_t nfds, int timeout);

🌸 DESCRIPTION 🌸

so bestie, qt_poll is a wrapper around the standard poll() system call function 💖 like, same vibe, same arguments, same energy. BUT. instead of just raw-dogging that blocking system call directly, the operation gets enqueued in the internal system call queue to be handled. no cap. 🔥

and why do we do this?? because the system call queue is literally the whole point: it's a way to perform blocking system calls without impeding parallel computation</>. so your other threads can keep doing their little computations while this one goes and waits. main character energy for the queue, honestly. 👑

so how does it work:

• operations get enqueued in an internal queue 📥
• that queue is serviced by a dynamic number of dedicated system call threads 🧚
• the number of threads in that set is capped at a user-configurable limit, which you specify with the QT_MAX_IO_WORKERS environment variable at initialization time ⭐
• when there are no more operations in the system call queue, those workers stay persistent for a configurable amount of time — set with the QT_IO_TIMEOUT environment variable, also at initialization time — before they exit 💀
• and why do they linger?? to reduce the overhead involved in scaling up the number of worker threads to respond to newly enqueued system calls 🎀

basically the workers are like "okay we'll hang around a bit in case you need us again" and honestly, relatable. the commitment. the loyalty. 🫶

ngl the two env vars that matter here are QT_MAX_IO_WORKERS (the cap) and QT_IO_TIMEOUT (how long idle workers stick around), and both get read at initialization time, so don't go changing them mid-run and expecting a glow-up. 🙈

👀 SEE ALSO 👀

• poll(2)
• qt_accept(3)
• qt_connect(3)
• qt_pread(3)
• qt_pwrite(3)
• qt_read(3)
• qt_select(3)
• qt_system(3)
• qt_wait4(3)
• qt_write(3)

like, the whole qt_ squad. go read them too, bestie. 💜

libqthread • AUGUST 2012 • qt_poll(3)

and that's the page!! mwah 💋 thanks for coming to my ted talk, go forth and multiplex synchronously, you absolute queen 🎀✨🦋