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	1	.\" Copyright (c) 1996 John Birrell <jb@cimlogic.com.au>.
	2	.\" All rights reserved.
	3	.\"
	4	.\" Redistribution and use in source and binary forms, with or without
	5	.\" modification, are permitted provided that the following conditions
	6	.\" are met:
	7	.\" 1. Redistributions of source code must retain the above copyright
	8	.\" notice, this list of conditions and the following disclaimer.
	9	.\" 2. Redistributions in binary form must reproduce the above copyright
	10	.\" notice, this list of conditions and the following disclaimer in the
	11	.\" documentation and/or other materials provided with the distribution.
	12	.\" 3. All advertising materials mentioning features or use of this software
	13	.\" must display the following acknowledgement:
	14	.\" This product includes software developed by John Birrell.
	15	.\" 4. Neither the name of the author nor the names of any co-contributors
	16	.\" may be used to endorse or promote products derived from this software
	17	.\" without specific prior written permission.
	18	.\"
	19	.\" THIS SOFTWARE IS PROVIDED BY JOHN BIRRELL AND CONTRIBUTORS ``AS IS'' AND
	20	.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
	21	.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
	22	.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
	23	.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
	24	.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
	25	.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
	26	.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
	27	.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
	28	.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
	29	.\" SUCH DAMAGE.
	30	.\"
	31	.\" $FreeBSD$
	32	.\"
	33	.Dd April 4, 1996
	34	.Dt PTHREAD_ONCE 3
	35	.Os
	36	.Sh NAME
	37	.Nm pthread_once
	38	.Nd dynamic package initialization
	39	.Sh SYNOPSIS
	40	.In pthread.h
	41	.Pp
	42	pthread_once_t
	43	.Fa once_control
	44	= PTHREAD_ONCE_INIT;
	45	.Ft int
	46	.Fn pthread_once "pthread_once_t once_control" "void (init_routine)(void)"
	47	.Sh DESCRIPTION
	48	The first call to
	49	.Fn pthread_once
	50	by any thread in a process, with a given
	51	.Fa once_control ,
	52	will call the
	53	.Fn init_routine
	54	with no arguments.
	55	Subsequent calls to
	56	.Fn pthread_once
	57	with the same
	58	.Fa once_control
	59	will not call the
	60	.Fn init_routine .
	61	On return from
	62	.Fn pthread_once ,
	63	it is guaranteed that
	64	.Fn init_routine
	65	has completed.
	66	The
	67	.Fa once_control
	68	parameter is used to determine whether the associated initialization
	69	routine has been called.
	70	.Pp
	71	The function
	72	.Fn pthread_once
	73	is not a cancellation point.
	74	However, if
	75	.Fn init_routine
	76	is a cancellation point and is cancelled, the effect on
	77	.Fa once_control
	78	is as if
	79	.Fn pthread_once
	80	was never called.
	81	.Pp
	82	The constant
	83	.Fa PTHREAD_ONCE_INIT
	84	is defined by header
	85	.In pthread.h .
	86	.Pp
	87	The behavior of
	88	.Fn pthread_once
	89	is undefined if
	90	.Fa once_control
	91	has automatic storage duration or is not initialized by
	92	.Fa PTHREAD_ONCE_INIT .
	93	.Sh RETURN VALUES
	94	If successful, the
	95	.Fn pthread_once
	96	function will return zero.
	97	Otherwise an error number will be returned to
	98	indicate the error.
	99	.Sh ERRORS
	100	None.
	101	.Sh STANDARDS
	102	The
	103	.Fn pthread_once
	104	function conforms to
	105	.St -p1003.1-96 .