NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
|
|
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-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
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