.\" Copyright (c) 2004 Michael Telahun Makonnen
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.Dd August 17, 2018
.Dt PTHREAD_BARRIER 3
.Os
.Sh NAME
.Nm pthread_barrier_destroy , pthread_barrier_init , pthread_barrier_wait
.Nd "destroy, initialize or wait on a barrier object"
.Sh LIBRARY
.Lb libpthread
.Sh SYNOPSIS
.In pthread.h
.Ft int
.Fn pthread_barrier_destroy "pthread_barrier_t *barrier"
.Ft int
.Fn pthread_barrier_init "pthread_barrier_t *restrict barrier" "const pthread_barrierattr_t *attr" "unsigned count"
.Ft int
.Fn pthread_barrier_wait "pthread_barrier_t *barrier"
.Sh DESCRIPTION
The
.Fn pthread_barrier_init
function will initialize
.Fa barrier
with attributes specified in
.Fa attr ,
or if it is
.Dv NULL ,
with default attributes.
The number of threads that must call
.Fn pthread_barrier_wait
before any of the waiting threads can be
released is specified by
.Fa count .
The
.Fn pthread_barrier_destroy
function will destroy
.Fa barrier
and release any resources that may have been allocated on its behalf.
.Pp
The
.Fn pthread_barrier_wait
function will synchronize calling threads at
.Fa barrier .
The threads will be blocked from
making further progress until
a sufficient number of threads calls this function.
The number of threads that must call it before
any of them will be released is determined by the
.Fa count
argument to
.Fn pthread_barrier_init .
Once the threads have been released the barrier will be reset.
.Sh IMPLEMENTATION NOTES
In
.Lb libthr
the
.Dv PTHREAD_BARRIER_SERIAL_THREAD
return value will
always be returned by the last thread to reach the barrier.
.Sh RETURN VALUES
If successful,
both
.Fn pthread_barrier_destroy
and
.Fn pthread_barrier_init
will return zero.
Otherwise, an error number will be returned to indicate the error.
If the call to
.Fn pthread_barrier_wait
is successful, all but one of the threads will return zero.
That one thread will return
.Dv PTHREAD_BARRIER_SERIAL_THREAD .
Otherwise, an error number will be returned to indicate the error.
.Pp
None of these functions will return
.Er EINTR .
.Sh ERRORS
The
.Fn pthread_barrier_destroy
function will fail if:
.Bl -tag -width Er
.It Bq Er EBUSY
An attempt was made to destroy
.Fa barrier
while it was in use.
.El
.Pp
The
.Fn pthread_barrier_destroy
and
.Fn pthread_barrier_wait
functions may fail if:
.Bl -tag -width Er
.It Bq Er EINVAL
The value specified by
.Fa barrier
is invalid.
.El
.Pp
The
.Fn pthread_barrier_init
function will fail if:
.Bl -tag -width Er
.It Bq Er EAGAIN
The system lacks resources,
other than memory,
to initialize
.Fa barrier .
.It Bq Er EINVAL
The
.Fa count
argument is less than 1.
.It Bq Er ENOMEM
Insufficient memory to initialize
.Fa barrier .
.El
.Sh SEE ALSO
.Xr pthread_barrierattr 3
.Sh HISTORY
The
.Fn pthread_barrier_destroy ,
.Fn pthread_barrier_init
and
.Fn pthread_barrier_wait
functions first appeared in
.Lb libkse
in
.Fx 5.2 ,
and in
.Lb libthr
in
.Fx 5.3 .