NAME

       FUTEX_FD - create a file descriptor associated with a futex

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>

       [[deprecated]]
       long syscall(SYS_futex, uint32_t *uaddr, FUTEX_FD, uint32_t val);

DESCRIPTION

       This  operation  creates  a  file descriptor that is associated with the futex at uaddr.  The caller must
       close the returned file descriptor after use.

       When another process or thread performs a FUTEX_WAKE(2const) on  the  futex  word,  the  file  descriptor
       indicates as being readable with select(2), poll(2), and epoll(7)

       The  file  descriptor  can  be  used  to obtain asynchronous notifications: if val is nonzero, then, when
       another process or thread executes a FUTEX_WAKE(2const), the caller will receive the signal  number  that
       was passed in val.

RETURN VALUE

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

       On success, FUTEX_FD Returns the new file descriptor associated with the futex.

ERRORS

       See futex(2).

       EINVAL The signal number supplied in val is invalid.

       ENFILE The system-wide limit on the total number of open files has been reached.

STANDARDS

       Linux.

HISTORY

       From Linux 2.6.0 up to and including Linux 2.6.25.

       Because it was inherently racy, FUTEX_FD has been removed from Linux 2.6.26 onward.

SEE ALSO

       futex(2)

Linux man-pages 6.16                               2025-05-30                                   FUTEX_FD(2const)