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.Dd May 26, 2008
.Dt PTHREAD_SPIN_LOCK 3
.Os
.Sh NAME
.Nm pthread_spin_lock ,
.Nm pthread_spin_trylock
.Nd acquire a spin lock
.Sh LIBRARY
.Lb libpthread
.Sh SYNOPSIS
.In pthread.h
.Ft int
.Fn pthread_spin_lock "pthread_spinlock_t *lock"
.Ft int
.Fn pthread_spin_trylock "pthread_spinlock_t *lock"
.Sh DESCRIPTION
The
.Fn pthread_spin_lock
function acquires a spin lock on
.Fa lock
provided that
.Fa lock
is not presently held.
If the lock cannot be
immediately acquired, the calling thread repeatedly retries until it can
acquire the lock.
.Pp
The
.Fn pthread_spin_trylock
function performs the same action, but does not block if the lock
cannot be immediately obtained (i.e., the lock is held).
.Sh RETURN VALUES
If successful, the
.Fn pthread_spin_lock
and
.Fn pthread_spin_trylock
functions will return zero.
Otherwise an error number will be returned to indicate the error.
.Sh ERRORS
The
.Fn pthread_spin_trylock
function shall fail if:
.Bl -tag -width Er
.It Bq Er EBUSY
The lock could not be acquired because a writer holds the lock or
was blocked on it.
.El
.Pp
The
.Fn pthread_spin_lock
function may fail if:
.Bl -tag -width Er
.It Bq Er EDEADLK
The current thread already owns
.Fa lock
for writing.
.El
.Pp
The
.Fn pthread_spin_lock
and
.Fn pthread_spin_trylock
functions may fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The value specified by
.Fa lock
is invalid.
.El
.Sh SEE ALSO
.Xr pthread_spin_destroy 3 ,
.Xr pthread_spin_init 3 ,
.Xr pthread_spin_unlock 3
.Sh STANDARDS
.Fn pthread_spin_lock
and
.Fn pthread_spin_trylock
conform to
.St -p1003.1-2001 .
.Sh CAVEATS
Applications using spinlocks are vulnerable to the effects of priority
inversion.
Applications using real-time threads
.Pq Dv SCHED_FIFO , SCHED_RR
should not use these interfaces.
Outside carefully controlled environments, priority inversion with spinlocks
can lead to system deadlock.
Mutexes are preferable in nearly every possible use case.