.\" Copyright (c) 2017, Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH pthread_spin_lock 3 2024-05-02 "Linux man-pages 6.9.1"
.SH NAME
pthread_spin_lock, pthread_spin_trylock, pthread_spin_unlock \-
lock and unlock a spin lock
.SH LIBRARY
POSIX threads library
.RI ( libpthread ", " \-lpthread )
.SH SYNOPSIS
.nf
.B #include <pthread.h>
.P
.BI "int pthread_spin_lock(pthread_spinlock_t *" lock );
.BI "int pthread_spin_trylock(pthread_spinlock_t *" lock );
.BI "int pthread_spin_unlock(pthread_spinlock_t *" lock );
.fi
.P
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.P
.BR pthread_spin_lock (),
.BR pthread_spin_trylock ():
.nf
    _POSIX_C_SOURCE >= 200112L
.fi
.SH DESCRIPTION
The
.BR pthread_spin_lock ()
function locks the spin lock referred to by
.IR lock .
If the spin lock is currently unlocked,
the calling thread acquires the lock immediately.
If the spin lock is currently locked by another thread,
the calling thread spins, testing the lock until it becomes available,
at which point the calling thread acquires the lock.
.P
Calling
.BR pthread_spin_lock ()
on a lock that is already held by the caller
or a lock that has not been initialized with
.BR pthread_spin_init (3)
results in undefined behavior.
.P
The
.BR pthread_spin_trylock ()
function is like
.BR pthread_spin_lock (),
except that if the spin lock referred to by
.I lock
is currently locked,
then, instead of spinning, the call returns immediately with the error
.BR EBUSY .
.P
The
.BR pthread_spin_unlock ()
function unlocks the spin lock referred to
.IR lock .
If any threads are spinning on the lock,
one of those threads will then acquire the lock.
.P
Calling
.BR pthread_spin_unlock ()
on a lock that is not held by the caller results in undefined behavior.
.SH RETURN VALUE
On success, these functions return zero.
On failure, they return an error number.
.SH ERRORS
.BR pthread_spin_lock ()
may fail with the following errors:
.TP
.B EDEADLOCK
.\" Not detected in glibc
The system detected a deadlock condition.
.P
.BR pthread_spin_trylock ()
fails with the following errors:
.TP
.B EBUSY
The spin lock is currently locked by another thread.
.SH STANDARDS
POSIX.1-2008.
.SH HISTORY
glibc 2.2.
POSIX.1-2001.
.SH CAVEATS
Applying any of the functions described on this page to
an uninitialized spin lock results in undefined behavior.
.P
Carefully read NOTES in
.BR pthread_spin_init (3).
.SH SEE ALSO
.ad l
.nh
.\" FIXME . .BR pthread_mutex_lock (3),
.BR pthread_spin_destroy (3),
.BR pthread_spin_init (3),
.BR pthreads (7)