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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | CAVEATS | SEE ALSO | COLOPHON |
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FUTEX_LOCK_PI(2const) FUTEX_LOCK_PI(2const)
FUTEX_LOCK_PI - lock a priority-inheritance futex
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_LOCK_PI, 0,
const struct timespec *timeout);
This operation is used after an attempt to acquire the lock via an
atomic user-mode instruction failed because the futex word has a
nonzero value—specifically, because it contained the (PID-
namespace-specific) TID of the lock owner.
The operation checks the value of the futex word at the address
uaddr. If the value is 0, then the kernel tries to atomically set
the futex value to the caller's TID. If the futex word's value is
nonzero, the kernel atomically sets the FUTEX_WAITERS bit, which
signals the futex owner that it cannot unlock the futex in user
space atomically by setting the futex value to 0. After that, the
kernel:
(1) Tries to find the thread which is associated with the owner
TID.
(2) Creates or reuses kernel state on behalf of the owner. (If
this is the first waiter, there is no kernel state for this
futex, so kernel state is created by locking the RT-mutex and
the futex owner is made the owner of the RT-mutex. If there
are existing waiters, then the existing state is reused.)
(3) Attaches the waiter to the futex (i.e., the waiter is
enqueued on the RT-mutex waiter list).
If more than one waiter exists, the enqueueing of the waiter is in
descending priority order. (For information on priority ordering,
see the discussion of the SCHED_DEADLINE, SCHED_FIFO, and SCHED_RR
scheduling policies in sched(7).) The owner inherits either the
waiter's CPU bandwidth (if the waiter is scheduled under the
SCHED_DEADLINE policy) or the waiter's priority (if the waiter is
scheduled under the SCHED_RR or SCHED_FIFO policy). This
inheritance follows the lock chain in the case of nested locking
and performs deadlock detection.
The timeout argument provides a timeout for the lock attempt. If
timeout is not NULL, the structure it points to specifies an
absolute timeout. If timeout is NULL, the operation will block
indefinitely.
On error, -1 is returned, and errno is set to indicate the error.
On success, FUTEX_LOCK_PI returns 0 if the futex was successfully
locked.
See futex(2).
EAGAIN The futex owner thread ID of uaddr 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.
EFAULT timeout did not point to a valid user-space address.
EINVAL The supplied timeout argument was invalid (tv_sec was less
than zero, or tv_nsec was not less than 1,000,000,000).
EINVAL The kernel detected an inconsistency between the user-space
state at uaddr and the kernel state. This indicates either
state corruption or that the kernel found a waiter on uaddr
which is waiting via FUTEX_WAIT(2const) or
FUTEX_WAIT_BITSET(2const).
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
uaddr. (This may be caused by a state corruption in user
space.)
ESRCH The thread ID in the futex word at uaddr does not exist.
ETIMEDOUT
The timeout expired before the operation completed.
Linux.
Linux 2.6.18.
Unlike other futex(2) operations, the timeout is measured against
the CLOCK_REALTIME clock.
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
man-pages@man7.org
Linux man-pages 6.15 2025-05-30 FUTEX_LOCK_PI(2const)
Pages that refer to this page: futex(2), FUTEX_CMP_REQUEUE(2const), FUTEX_CMP_REQUEUE_PI(2const), FUTEX_LOCK_PI2(2const), FUTEX_REQUEUE(2const), FUTEX_UNLOCK_PI(2const), FUTEX_WAIT_BITSET(2const), FUTEX_WAKE(2const), FUTEX_WAKE_OP(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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