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 6.16                               2025-05-30                                 FUTEX_WAKE(2const)