<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <HTML> <HEAD> <META HTTP-EQUIV="CONTENT-TYPE" CONTENT="text/html; charset=utf-8"> <TITLE>PTHREAD_ONCE(3) manual page</TITLE> <META NAME="GENERATOR" CONTENT="OpenOffice.org 1.1.3 (Linux)"> <META NAME="CREATED" CONTENT="20050505;322600"> <META NAME="CHANGED" CONTENT="20050603;463100"> <!-- manual page source format generated by PolyglotMan v3.2, --> <!-- available at http://polyglotman.sourceforge.net/ --> </HEAD> <BODY LANG="en-GB" BGCOLOR="#ffffff" DIR="LTR"> <H4>POSIX Threads for Windows – REFERENCE - <A HREF="http://sources.redhat.com/pthreads-win32">Pthreads-w32</A></H4> <P><A HREF="index.html">Reference Index</A></P> <P><A HREF="#toc">Table of Contents</A></P> <H2><A HREF="#toc0" NAME="sect0">Name</A></H2> <P>pthread_once - once-only initialization </P> <H2><A HREF="#toc1" NAME="sect1">Synopsis</A></H2> <P><B>#include <pthread.h></B> </P> <P><B>pthread_once_t </B><I>once_control</I> <B>= PTHREAD_ONCE_INIT;</B> </P> <P><B>int pthread_once(pthread_once_t *</B><I>once_control</I><B>, void (*</B><I>init_routine</I><B>) (void));</B> </P> <H2><A HREF="#toc2" NAME="sect2">Description</A></H2> <P>The purpose of <B>pthread_once</B> is to ensure that a piece of initialization code is executed at most once. The <I>once_control</I> argument points to a static or extern variable statically initialized to <B>PTHREAD_ONCE_INIT</B>. </P> <P>The first time <B>pthread_once</B> is called with a given <I>once_control</I> argument, it calls <I>init_routine</I> with no argument and changes the value of the <I>once_control</I> variable to record that initialization has been performed. Subsequent calls to <B>pthread_once</B> with the same <B>once_control</B> argument do nothing. </P> <H2><A HREF="#toc3" NAME="sect3">Cancellation</A></H2> <P>While <B>pthread_once</B> is not a cancellation point, <I>init_routine</I> can be. The effect on <I>once_control</I> of a cancellation inside the <I>init_routine</I> is to leave it as if <B>pthread_once</B> had not been called by the cancelled thread.</P> <H2><A HREF="#toc4" NAME="sect4">Return Value</A></H2> <P STYLE="text-decoration: none"><FONT COLOR="#000000"><B>pthread_once</B> returns 0 on success, or an error code on failure.</FONT></P> <H2><A HREF="#toc5" NAME="sect5">Errors</A></H2> <P>The <B>pthread_once</B> function returns the following error code on error: </P> <DL> <DL> <DT STYLE="margin-right: 1cm; margin-bottom: 0.5cm"><B>EINVAL</B> </DT></DL> </DL> <P STYLE="margin-left: 2cm"> The once_control or init_routine parameter is NULL.</P> <H2><A HREF="#toc6" NAME="sect6">Author</A></H2> <P>Xavier Leroy <Xavier.Leroy@inria.fr> </P> <P>Modified by Ross Johnson for use with <A HREF="http://sources.redhat.com/pthreads-win32">Pthreads-w32</A>.</P> <HR> <P><A NAME="toc"></A><B>Table of Contents</B></P> <UL> <LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect0" NAME="toc0">Name</A> </P> <LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect1" NAME="toc1">Synopsis</A> </P> <LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect2" NAME="toc2">Description</A> </P> <LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect3" NAME="toc3">Cancellation</A> </P> <LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect4" NAME="toc4">Return Value</A> </P> <LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect5" NAME="toc5">Errors</A> </P> <LI><P><A HREF="#sect6" NAME="toc6">Author</A> </P> </UL> </BODY> </HTML>