\" $NetBSD: pthread_barrier.3,v 1.8 2017/10/22 16:15:02 abhinav Exp $

\" $NetBSD: pthread_barrier.3,v 1.8 2017/10/22 16:15:02 abhinav Exp $
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\" ----------------------------------------------------------------------------
Dd October 22, 2017
Dt PTHREAD_BARRIER 3
Os
Sh NAME
Nm pthread_barrier ,
Nm pthread_barrier_init ,
Nm pthread_barrier_destroy ,
Nm pthread_barrier_wait
Nd barrier interface
Sh LIBRARY
Lb libpthread
Sh SYNOPSIS
In pthread.h
Ft int
Fn pthread_barrier_init "pthread_barrier_t * restrict barrier" \
"const pthread_barrierattr_t * restrict attr" "unsigned int count"
Ft int
Fn pthread_barrier_destroy "pthread_barrier_t *barrier"
Ft int
Fn pthread_barrier_wait "pthread_barrier_t *barrier"
\" ----------------------------------------------------------------------------
Sh DESCRIPTION
The
Fn pthread_barrier_init
function creates a new barrier with attributes
Fa attr
and
Fa count .
The
Fa count
parameter indicates the number of threads
which will participate in the barrier.
The
Xr pthread_barrierattr_init 3
function may be used to specify the attributes supplied in
Fa attr .
If
Fa attr
is
Dv NULL ,
the default attributes are used.
Barriers are most commonly used in the decomposition of parallel loops.
Pp
\" -----
The
Fn pthread_barrier_destroy
function causes the resources allocated to
Fa barrier
to be released.
No threads should be blocked on
Fa barrier .
Pp
\" -----
The
Fn pthread_barrier_wait
function causes the current thread to wait on the barrier specified.
Once as many threads as specified by the
Fa count
parameter to the corresponding
Fn pthread_barrier_init
call have called
Fn pthread_barrier_wait ,
all threads will wake up, return from their respective
Fn pthread_barrier_wait
calls and continue execution.
\" -----
\" ----------------------------------------------------------------------------
Sh RETURN VALUES
If successful,
Fn pthread_barrier_init
will return zero and put the new barrier id into
Fa barrier ,
otherwise an error number will be returned to indicate the error.
Pp
\" -----
If successful,
Fn pthread_barrier_destroy
will return zero.
Otherwise an error value will be returned.
Pp
\" -----
If successful,
Fn pthread_barrier_wait
will return zero for all waiting threads except for one.
One thread will receive status
Dv PTHREAD_BARRIER_SERIAL_THREAD ,
which is intended to indicate that this thread may be used to update
shared data.
It is the responsibility of this thread to insure the visibility
and atomicity of any updates to shared data with respect to the
other threads participating in the barrier.
In the case of failure, an error value will be returned.
\" ----------------------------------------------------------------------------
Sh ERRORS
The
Fn pthread_barrier_init
function may fail if:
Bl -tag -width Er
It Bq Er EINVAL
The value specified by
Fa count
is zero or
Fa attr
is invalid.
El
Pp
\" -----
The
Fn pthread_barrier_destroy
function may fail if:
Bl -tag -width Er
It Bq Er EBUSY
The
Fa barrier
still has active threads associated with it.
It Bq Er EINVAL
The value specified by
Fa barrier
is invalid.
El
Pp
\" -----
The
Fn pthread_barrier_wait
function may fail if:
Bl -tag -width Er
It Bq Er EINVAL
The value specified by
Fa barrier
is invalid.
El
\" ---------------------------------------------------------------------------
Sh SEE ALSO
Xr pthread_barrierattr 3 ,
Xr pthread_cond 3 ,
Xr pthread_mutex 3
Sh STANDARDS
These functions conform to
St -p1003.1-2001 .