.\" $NetBSD: pthread_once.3,v 1.3 2008/05/02 18:11:04 martin Exp $
.\"
.\" Copyright (c) 2002 The NetBSD Foundation, Inc.
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.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" Copyright (c) 1996 John Birrell <jb@cimlogic.com.au>.
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by John Birrell.
.\" 4. Neither the name of the author nor the names of any co-contributors
.\"    may be used to endorse or promote products derived from this software
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" $FreeBSD: src/lib/libpthread/man/pthread_once.3,v 1.14 2002/09/16 19:29:29 mini Exp $
.\"
.Dd January 30, 2003
.Dt PTHREAD_ONCE 3
.Os
.Sh NAME
.Nm pthread_once
.Nd dynamic package initialization
.Sh LIBRARY
.Lb libpthread
.Sh SYNOPSIS
.In pthread.h
.Pp
pthread_once_t
.Fa once_control
= PTHREAD_ONCE_INIT;
.Ft int
.Fn pthread_once "pthread_once_t *once_control" "void (*init_routine)(void)"
.Sh DESCRIPTION
The first call to
.Fn pthread_once
by any thread in a process, with a given
.Fa once_control ,
will call the
.Fn init_routine
with no arguments.
Subsequent calls to
.Fn pthread_once
with the same
.Fa once_control
will not call the
.Fn init_routine .
On return from
.Fn pthread_once ,
it is guaranteed that
.Fn init_routine
has completed.
The
.Fa once_control
parameter is used to determine whether the associated initialization
routine has been called.
.Pp
The function
.Fn pthread_once
is not a cancellation point.
However, if
.Fn init_routine
is a cancellation point and is cancelled, the effect on
.Fa once_control
is as if
.Fn pthread_once
was never called.
.Pp
The constant
.Fa PTHREAD_ONCE_INIT
is defined by header
.Aq Pa pthread.h .
.Pp
The behavior of
.Fn pthread_once
is undefined if
.Fa once_control
has automatic storage duration or is not initialized by
.Fa PTHREAD_ONCE_INIT .
.Sh RETURN VALUES
If successful,  the
.Fn pthread_once
function will return zero.
Otherwise an error number will be returned to
indicate the error.
.Sh ERRORS
None.
.Sh STANDARDS
.Fn pthread_once
conforms to
.St -p1003.1-96 .