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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
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FUTEX_CMP_REQUEUE_PI(2const) FUTEX_CMP_REQUEUE_PI(2const)
FUTEX_CMP_REQUEUE_PI - compare a priority-inheritance futex, wake
a waiter, and requeue others
Standard C library (libc, -lc)
#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_CMP_REQUEUE_PI, 1,
uint32_t val2, uint32_t *uaddr2,
uint32_t val3);
This operation is a PI-aware variant of FUTEX_CMP_REQUEUE(2const).
It requeues waiters that are blocked via
FUTEX_WAIT_REQUEUE_PI(2const) on uaddr from a non-PI source futex
(uaddr) to a PI target futex (uaddr2).
Unlike with FUTEX_CMP_REQUEUE(2const), this operation wakes up a
maximum of 1 waiter that is waiting on the futex at uaddr (since
the main point is to avoid a thundering herd). The remaining
waiters are removed from the wait queue of the source futex at
uaddr and added to the wait queue of the target futex at uaddr2.
The val2 and val3 arguments serve the same purposes as for
FUTEX_CMP_REQUEUE(2const).
On error, -1 is returned, and errno is set to indicate the error.
On success, FUTEX_CMP_REQUEUE_PI Returns the total number of
waiters that were woken up or requeued to the futex for the futex
word at uaddr2. If this value is greater than 1, then difference
is the number of waiters requeued to the futex for the futex word
at uaddr2.
See futex(2).
EAGAIN The value pointed to by uaddr is not equal to the expected
value val3.
EAGAIN The futex owner thread ID of uaddr2 is about to exit, but
has not yet handled the internal state cleanup. Try again.
EDEADLK
The futex word at uaddr is already locked by the caller.
EDEADLK
While requeueing a waiter to the PI futex for the futex
word at uaddr2, the kernel detected a deadlock.
EFAULT uaddr2 did not point to a valid user-space address.
EINVAL uaddr2 does not point to a valid object—that is, the
address is not four-byte-aligned.
EINVAL uaddr equals uaddr2 (i.e., an attempt was made to requeue
to the same futex).
EINVAL The kernel detected an inconsistency between the user-space
state at uaddr2 and the kernel state; that is, the kernel
detected a waiter which waits via FUTEX_WAIT(2const) or
FUTEX_WAIT_BITSET(2const) on uaddr2.
EINVAL The kernel detected an inconsistency between the user-space
state at uaddr and the kernel state; that is, the kernel
detected a waiter which waits via FUTEX_WAIT(2const) or
FUTEX_WAIT_BITSET(2const) on uaddr.
EINVAL The kernel detected an inconsistency between the user-space
state at uaddr and the kernel state; that is, the kernel
detected a waiter which waits on uaddr via
FUTEX_LOCK_PI(2const) or FUTEX_LOCK_PI2(2const) (instead of
FUTEX_WAIT_REQUEUE_PI).
EINVAL An attempt was made to requeue a waiter to a futex other
than that specified by the matching FUTEX_WAIT_REQUEUE_PI
call for that waiter.
EINVAL The fourth argument is not 1.
ENOMEM The kernel could not allocate memory to hold state
information.
ENOSYS A run-time check determined that the operation is not
available. The PI-futex operations are not implemented on
all architectures and are not supported on some CPU
variants.
EPERM The caller is not allowed to attach itself to the futex at
uaddr2. (This may be caused by a state corruption in user
space.)
ESRCH The thread ID in the futex word at uaddr does not exist.
ESRCH The thread ID in the futex word at uaddr2 does not exist.
Linux.
Linux 2.6.31.
futex(2)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
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improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-30 FUTEX_CMP_REQUEUE_PI(2const)
Pages that refer to this page: futex(2), FUTEX_WAIT_REQUEUE_PI(2const)
Copyright and license for this manual page
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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