io_uring_prep_futex_wait(3) liburing Manual io_uring_prep_futex_wait(3)

io_uring_prep_futex_wait - prepare a futex wait request

#include <linux/futex.h>
#include <unistd.h>
#include <liburing.h>
void io_uring_prep_futex_wait(struct io_uring_sqe *sqe,
                              uint32_t *futex,
                              uint64_t val,
                              uint64_t mask,
                              uint32_t futex_flags,
                              unsigned int flags);

The io_uring_prep_futex_wait(3) function prepares a futex wait request. The submission queue entry sqe is setup for waiting on a futex at address futex and which still has the value val and with futex2(2) flags of futex_flags and io_uring futex flags of flags .

mask can be set to a specific bitset mask, which will be matched by the waking side to decide who to wake up. To always get woken, an application may use FUTEX_BITSET_MATCH_ANY .

futex_flags follows the futex2(2) flags, not the futex(2) v1 interface flags.

flags are currently unused and hence 0 must be passed.

This function prepares an async futex(2) wait request. See that man page for details. Note that the io_uring futex wait request is similar to the FUTEX_WAIT_BITSET operation, as FUTEX_WAIT is a strict subset of that.


The CQE res field will contain the result of the operation. See the related man page for details on possible values. Note that where synchronous system calls will return -1 on failure and set errno to the actual error value, io_uring never uses errno. Instead it returns the negated errno directly in the CQE res field.

Unlike the sync futex syscalls that wait on a futex, io_uring does not support passing in a timeout for the request. Instead, applications are encouraged to use a linked timeout to abort the futex request at a given time, if desired.

io_uring_get_sqe(3), io_uring_submit(3), io_uring_prep_futex_waitv(3), io_uring_prep_futex_wake(3), io_uring_prep_link_timeout(3), futex(2) futex2(2)

September 29, 2023 liburing-2.5