---
name: "io_uring_prep_futex_wait"
section: "3"
platform: "linux"
package: "liburing"
version: "2.15-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/io_uring_prep_futex_wait"
---

# io\_uring\_prep\_futex\_wait(3)

prepare a futex wait request

## NAME

io\_uring\_prep\_futex\_wait - prepare a futex wait request

## SYNOPSIS

```
#include <linux/futex.h>
#include <unistd.h>
#include <liburing.h>
```

**void io\_uring\_prep\_futex\_wait(struct io\_uring\_sqe \****sqe***,**                               **const uint32\_t \****futex***,**                               **uint64\_t** *val***,**                               **uint64\_t** *mask***,**                               **uint32\_t** *futex\_flags***,**                               **unsigned int** *flags***);**

## DESCRIPTION

The [**io\_uring\_prep\_futex\_wait**(3)](/io_uring_prep_futex_wait/3.md) 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)](/futex/2.md) v1 interface flags.

*flags* are currently unused and hence **0** must be passed.

This function prepares an async [**futex**(2)](/futex/2.md) 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.

Available since kernel 6.7.

## RETURN VALUE

None

## ERRORS

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.

## NOTES

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.

## SEE ALSO

[**io\_uring\_get\_sqe**(3)](/io_uring_get_sqe/3.md), [**io\_uring\_submit**(3)](/io_uring_submit/3.md), [**io\_uring\_prep\_futex\_waitv**(3)](/io_uring_prep_futex_waitv/3.md), [**io\_uring\_prep\_futex\_wake**(3)](/io_uring_prep_futex_wake/3.md), [**io\_uring\_prep\_link\_timeout**(3)](/io_uring_prep_link_timeout/3.md), [**futex**(2)](/futex/2.md) **futex2**(2)