FUTEX_WAKE(2const)                                          FUTEX_WAKE(2const)

NAME
       FUTEX_WAKE - wake waiters that are inside FUTEX_WAIT

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <linux/futex.h>  /* Definition of FUTEX_* constants */
       #include <sys/syscall.h>  /* Definition of SYS_* constants */
       #include <unistd.h>

       long syscall(SYS_futex, uint32_t *uaddr, FUTEX_WAKE, uint32_t val);

DESCRIPTION
       This operation wakes at most val of the waiters that are waiting (e.g.,
       inside FUTEX_WAIT(2const)) on the futex word at the address uaddr.

       Most commonly, val is specified as either 1 (wake up a single waiter)
       or INT_MAX (wake up all waiters).

       No guarantee is provided about which waiters are awoken (e.g., a waiter
       with a higher scheduling priority is not guaranteed to be awoken in
       preference to a waiter with a lower priority).

RETURN VALUE
       On error, -1 is returned, and errno is set to indicate the error.

       On success, FUTEX_WAKE returns the number of waiters that were woken
       up.

ERRORS
       See futex(2).

       EINVAL The kernel detected an inconsistency between the user-space
              state at uaddr and the kernel state--that is, it detected a
              waiter which waits in FUTEX_LOCK_PI(2const) or
              FUTEX_LOCK_PI2(2const) on uaddr.

STANDARDS
       Linux.

HISTORY
       Linux 2.6.0.

SEE ALSO
       futex(2)

Linux man-pages 6.15              2025-05-30                FUTEX_WAKE(2const)