qthread_syncvar_readFE(3)

💖 qthread_syncvar_readFE — from libqthread (section 3) 💖

okay bestie, sit down, hydrate, and let's talk about the most dramatic little function in libqthread 🫶

✨ NAME ✨

qthread_syncvar_readFE — she waits for the syncvar to be full, then copies its data and empties it 💅

🌸 SYNOPSIS 🌸

#include <qthread.h>

int
qthread_syncvar_readFE (uint64_t * restrict dest, syncvar_t * restrict
src);

🦋 DESCRIPTION 🦋

So here's the vibe: this function waits for memory to become full, and then empties it. That's the whole personality. 🎀

When memory becomes full, only one thread blocked like this will be awoken. Not two. Not "whoever gets there first." One. The others stay seated, bestie. 💀

Data is read from src and stored in dest. And here's the cute part — dest may be NULL, in which case the data will not be copied. She just empties. No notes. 🙈

The semantics of readFE are, in order:

1. src's FEB state must be "full" ⭐
2. data is copied from src to dest ✨
3. src's FEB state gets changed from "full" to "empty" 💅

it's giving full → copy → empty, and honestly? iconic. periodt.

🔥 RETURN VALUE 🔥

On success: the memory address src is marked empty, the memory address dest is filled with the contents of src, and 0 (QTHREAD_SUCCESS) is returned. slay. 🎉

On error: a non-zero error code is returned. not slay, but at least you know. 😭

💜 ERRORS 💜

• ENOMEM — Not enough memory could be allocated for bookkeeping structures. she tried to set up her little admin and there was just nothing left in the budget. 💀
• QTHREAD_TIMEOUT — Could not obtain the lock on the syncvar_t's status bits. This may be caused by many things, including memory corruption, an invalid syncvar, or even absurdly excessive contention (because it's protected by a naive spinlock rather than a fair spinlock). ngl, the naive spinlock is the villain of this story. 🙈

🌈 SEE ALSO 🌈

• qthread_syncvar_empty(3)
• qthread_syncvar_fill(3)
• qthread_syncvar_writeFE(3)
• qthread_syncvar_writeF(3)
• qthread_syncvar_readFF(3)
• qthread_syncvar_status(3)

go read the whole friend group, they're all connected iykyk 👑

💖 cute sign-off: this page came from libqthread, dated APRIL 2011 — yes she's vintage, yes she still ate. mwah. 🎀💅✨