.\" $NetBSD: pthread_spin_init.3,v 1.8 2008/05/26 08:45:55 wiz Exp $
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.Dd May 26, 2008
.Dt PTHREAD_SPIN_INIT 3
.Os
.Sh NAME
.Nm pthread_spin_init
.Nd initialize a spin lock
.Sh LIBRARY
.Lb libpthread
.Sh SYNOPSIS
.In pthread.h
.Ft int
.Fn pthread_spin_init "pthread_spinlock_t *lock" "int pshared"
.Sh DESCRIPTION
The
.Fn pthread_spin_init
function is used to initialize a spinlock.
The
.Fa pshared
parameter is currently unused and all spinlocks exhibit the
.Dv PTHREAD_PROCESS_SHARED
property.
.Pp
The results of calling
.Fn pthread_spin_init
with an already initialized lock are undefined.
.Sh RETURN VALUES
If successful, the
.Fn pthread_spin_init
function will return zero.
Otherwise an error number will be returned to indicate the error.
.Sh ERRORS
The
.Fn pthread_spin_init
function shall fail if:
.Bl -tag -width Er
.It Bq Er ENOMEM
Insufficient memory exists to initialize the lock.
.El
.Pp
The
.Fn pthread_spin_init
function may fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The
.Fa lock
parameter was NULL or the
.Fa pshared
parameter was neither
.Dv PTHREAD_PROCESS_SHARED
nor
.Dv PTHREAD_PROCESS_PRIVATE .
.El
.Sh SEE ALSO
.Xr pthread_spin_destroy 3 ,
.Xr pthread_spin_lock 3 ,
.Xr pthread_spin_trylock 3 ,
.Xr pthread_spin_unlock 3
.Sh STANDARDS
.Fn pthread_spin_init
conforms 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.