.\" $NetBSD: pthread_once.3,v 1.9 2012/11/12 23:28:11 uwe Exp $
.\"
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.\" Copyright (c) 1996 John Birrell <jb@cimlogic.com.au>.
.\" All rights reserved.
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.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
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.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by John Birrell.
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.\"    may be used to endorse or promote products derived from this software
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.\" $FreeBSD: src/lib/libpthread/man/pthread_once.3,v 1.14 2002/09/16 19:29:29 mini Exp $
.\"
.Dd July 9, 2010
.Dt PTHREAD_ONCE 3
.Os
.Sh NAME
.Nm pthread_once
.Nd dynamic package initialization
.Sh LIBRARY
.Lb libpthread
.Sh SYNOPSIS
.In pthread.h
.Ft int
.Fn pthread_once "pthread_once_t *once_control" "void (*init_routine)(void)"
.Vt pthread_once_t once_control No = Dv PTHREAD_ONCE_INIT;
.Sh DESCRIPTION
The first call to
.Fn pthread_once
by any thread in a process, with a given
.Fa once_control ,
will call the
.Fa init_routine Ns ()
with no arguments.
Subsequent calls to
.Fn pthread_once
with the same
.Fa once_control
will not call the
.Fa init_routine Ns ().
On return from
.Fn pthread_once ,
it is guaranteed that
.Fa init_routine Ns ()
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
.Fa init_routine Ns ()
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
.Dv PTHREAD_ONCE_INIT
initializes the static once synchronization control structure
.Fa once_control
to be used with
.Fn pthread_once .
The behavior of
.Fn pthread_once
is undefined if
.Fa once_control
has automatic storage duration or is not initialized by
.Dv 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
The function conforms to
.St -p1003.1-2001 .