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.TH FUTEX_UNLOCK_PI 2const 2025-05-30 "Linux man-pages 6.16"
.SH NAME
FUTEX_UNLOCK_PI \- unlock a priority‐inheritance futex
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.BR "#include <linux/futex.h>" "  /* Definition of " FUTEX_* " constants */"
.BR "#include <sys/syscall.h>" "  /* Definition of " SYS_* " constants */"
.B #include <unistd.h>
.P
.BI "long syscall(SYS_futex, uint32_t *" uaddr ", FUTEX_UNLOCK_PI);"
.fi
.SH DESCRIPTION
This operation wakes the top priority waiter that is waiting in
.BR FUTEX_LOCK_PI (2const)
or
.BR FUTEX_LOCK_PI2 (2const)
on the futex address provided by the
.I uaddr
argument.
.P
This is called when the user-space value at
.I uaddr
cannot be changed atomically from a TID (of the owner) to 0.
.\"
.SH RETURN VALUE
On error,
\-1 is returned,
and
.I errno
is set to indicate the error.
.P
On success,
.B FUTEX_UNLOCK_PI
returns 0 if the futex was successfully unlocked.
.SH ERRORS
See
.BR futex (2).
.TP
.B EINVAL
The kernel detected an inconsistency between the user-space state at
.I uaddr
and the kernel state.
This indicates either state corruption
or that the kernel found a waiter on
.I uaddr
which is waiting via
.BR FUTEX_WAIT (2const)
or
.BR FUTEX_WAIT_BITSET (2const).
.TP
.B 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.
.TP
.B EPERM
The caller does not own the lock represented by the futex word.
.SH STANDARDS
Linux.
.SH HISTORY
Linux 2.6.18.
.\" commit c87e2837be82df479a6bae9f155c43516d2feebc
.SH SEE ALSO
.BR futex (2)