<!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_MUTEXATTR(3) manual page</TITLE> <META NAME="GENERATOR" CONTENT="OpenOffice.org 3.2 (Linux)"> <META NAME="CREATED" CONTENT="20050504;23040500"> <META NAME="CHANGEDBY" CONTENT="Ross Johnson"> <META NAME="CHANGED" CONTENT="20110326;13190500"> <!-- manual page source format generated by PolyglotMan v3.2, --> <!-- available at http://polyglotman.sourceforge.net/ --> <STYLE TYPE="text/css"> <!-- H4.cjk { font-family: "AR PL UMing CN" } H4.ctl { font-family: "Lohit Devanagari" } H2.cjk { font-family: "AR PL UMing CN" } H2.ctl { font-family: "Lohit Devanagari" } --> </STYLE> </HEAD> <BODY LANG="en-GB" BGCOLOR="#ffffff" DIR="LTR"> <H4 CLASS="western">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 CLASS="western"><A HREF="#toc0" NAME="sect0">Name</A></H2> <P>pthread_mutexattr_init, pthread_mutexattr_destroy, pthread_mutexattr_settype, pthread_mutexattr_gettype - mutex creation attributes </P> <H2 CLASS="western"><A HREF="#toc1" NAME="sect1">Synopsis</A></H2> <P><B>#include <pthread.h></B> </P> <P><B>int pthread_mutexattr_init(pthread_mutexattr_t *</B><I>attr</I><B>);</B> </P> <P><B>int pthread_mutexattr_destroy(pthread_mutexattr_t *</B><I>attr</I><B>);</B> </P> <P><B>int pthread_mutexattr_settype(pthread_mutexattr_t *</B><I>attr</I><B>, int </B><I>type</I><B>);</B> </P> <P><B>int pthread_mutexattr_gettype(const pthread_mutexattr_t *</B><I>attr</I><B>, int *</B><I>type</I><B>);</B> </P> <P><B>int pthread_mutexattr_setkind_np(pthread_mutexattr_t *</B><I>attr</I><B>, int </B><I>type</I><B>);</B> </P> <P><B>int pthread_mutexattr_getkind_np(const pthread_mutexattr_t *</B><I>attr</I><B>, int *</B><I>type</I><B>);</B> </P> <P><B>int pthread_mutexattr_setrobust(pthread_mutexattr_t *</B><I>attr</I><B>, int</B><SPAN STYLE="font-weight: normal"> </SPAN><I><SPAN STYLE="font-weight: normal">robust</SPAN></I><B>);</B> </P> <P><B>int pthread_mutexattr_getrobust(pthread_mutexattr_t *</B><I>attr</I><B>, int</B><SPAN STYLE="font-weight: normal"> </SPAN><B>*</B><I><SPAN STYLE="font-weight: normal">robust</SPAN></I><B>);</B> </P> <H2 CLASS="western"><A HREF="#toc2" NAME="sect2">Description</A></H2> <P>Mutex attributes can be specified at mutex creation time, by passing a mutex attribute object as second argument to <A HREF="pthread_mutex_init.html"><B>pthread_mutex_init</B>(3)</A> . Passing <B>NULL</B> is equivalent to passing a mutex attribute object with all attributes set to their default values. </P> <P><B>pthread_mutexattr_init</B> initializes the mutex attribute object <I>attr</I> and fills it with default values for the attributes. </P> <P><B>pthread_mutexattr_destroy</B> destroys a mutex attribute object, which must not be reused until it is reinitialized.</P> <P><B>pthread_mutexattr_settype</B> sets the mutex type attribute in <I>attr</I> to the value specified by <I>type</I>. </P> <P><B>pthread_mutexattr_gettype</B> retrieves the current value of the mutex kind attribute in <I>attr</I> and stores it in the location pointed to by <I>type</I>. </P> <P><B>Pthreads-w32</B> also recognises the following equivalent functions that are used in Linux:</P> <P><B>pthread_mutexattr_setkind_np</B> is an alias for <B>pthread_mutexattr_settype</B>. </P> <P STYLE="font-weight: normal"><B>pthread_mutexattr_getkind_np</B> is an alias for <B>pthread_mutexattr_gettype</B>. </P> <P>The following mutex types are supported:</P> <P STYLE="margin-left: 0.79in"><B>PTHREAD_MUTEX_NORMAL</B> - for ‘‘fast’’ mutexes.</P> <P STYLE="margin-left: 0.79in"><B>PTHREAD_MUTEX_RECURSIVE</B> - for ‘‘recursive’’ mutexes.</P> <P STYLE="margin-left: 0.79in"><B>PTHREAD_MUTEX_ERRORCHECK</B> - for ‘‘error checking’’ mutexes.</P> <P>The mutex type determines what happens if a thread attempts to lock a mutex it already owns with <A HREF="pthread_mutex_lock.html"><B>pthread_mutex_lock</B>(3)</A> . If the mutex is of the “normal” or “fast” type, <A HREF="pthread_mutex_lock.html"><B>pthread_mutex_lock</B>(3)</A> simply suspends the calling thread forever. If the mutex is of the ‘‘error checking’’ type, <A HREF="pthread_mutex_lock.html"><B>pthread_mutex_lock</B>(3)</A> returns immediately with the error code <B>EDEADLK</B>. If the mutex is of the ‘‘recursive’’ type, the call to <A HREF="pthread_mutex_lock.html"><B>pthread_mutex_lock</B>(3)</A> returns immediately with a success return code. The number of times the thread owning the mutex has locked it is recorded in the mutex. The owning thread must call <A HREF="pthread_mutex_unlock.html"><B>pthread_mutex_unlock</B>(3)</A> the same number of times before the mutex returns to the unlocked state. </P> <P>The default mutex type is <B>PTHREAD_MUTEX_NORMAL</B></P> <P><B>Pthreads-w32</B> also recognises the following equivalent types that are used by Linux:</P> <P STYLE="margin-left: 0.79in; font-weight: normal"><B>PTHREAD_MUTEX_FAST_NP</B> – equivalent to <B>PTHREAD_MUTEX_NORMAL</B></P> <P STYLE="margin-left: 0.79in"><B>PTHREAD_MUTEX_RECURSIVE_NP</B></P> <P STYLE="margin-left: 0.79in"><B>PTHREAD_MUTEX_ERRORCHECK_NP</B></P> <P><B>pthread_mutexattr_setrobust</B><SPAN STYLE="font-weight: normal"> sets the robustness attribute to the value given by </SPAN><I><SPAN STYLE="font-weight: normal">robust</SPAN></I><SPAN STYLE="font-weight: normal">.</SPAN></P> <P><B>pthread_mutexattr_getrobust</B><SPAN STYLE="font-weight: normal"> returns the current robustness value to the location given by *</SPAN><I><SPAN STYLE="font-weight: normal">robust</SPAN></I><SPAN STYLE="font-weight: normal">.</SPAN></P> <P><SPAN STYLE="font-weight: normal">The possible values for </SPAN><I><SPAN STYLE="font-weight: normal">robust</SPAN></I><SPAN STYLE="font-weight: normal"> are:</SPAN></P> <P STYLE="margin-left: 0.79in"><B>PTHREAD_MUTEX_STALLED</B><SPAN STYLE="font-weight: normal"> - when the owner of the mutex terminates without unlocking the mutex, all subsequent calls to pthread_mutex_*lock() are blocked from progress in an unspecified manner.</SPAN></P> <P STYLE="margin-left: 0.79in"><B>PTHREAD_MUTEX_ROBUST</B><SPAN STYLE="font-weight: normal"> - when the owner of the mutex terminates without unlocking the mutex, the mutex is unlocked. The next owner of this mutex acquires the mutex with an error return of EOWNERDEAD.</SPAN></P> <H2 CLASS="western"><A HREF="#toc3" NAME="sect3">Return Value</A></H2> <P><SPAN STYLE="font-weight: normal">On success all functions return 0, otherwise they return an error code as follows:</SPAN></P> <P><B>pthread_mutexattr_init</B></P> <P STYLE="margin-left: 0.79in"><B>ENOMEM</B><SPAN STYLE="font-weight: normal"> - insufficient memory for </SPAN><I><SPAN STYLE="font-weight: normal">attr</SPAN></I><SPAN STYLE="font-weight: normal">.</SPAN></P> <P><B>pthread_mutexattr_destroy</B></P> <P STYLE="margin-left: 0.79in"><B>EINVAL</B><SPAN STYLE="font-weight: normal"> - </SPAN><I><SPAN STYLE="font-weight: normal">attr</SPAN></I><SPAN STYLE="font-weight: normal"> is invalid.</SPAN></P> <P><B>pthread_mutexattr_gettype</B></P> <P STYLE="margin-left: 0.79in"><B>EINVAL</B><SPAN STYLE="font-weight: normal"> - </SPAN><I><SPAN STYLE="font-weight: normal">attr</SPAN></I><SPAN STYLE="font-weight: normal"> is invalid.</SPAN></P> <P><B>pthread_mutexattr_settype</B></P> <DL> <DL> <DL> <DT><B>EINVAL</B><SPAN STYLE="font-weight: normal"> - </SPAN><I><SPAN STYLE="font-weight: normal">attr</SPAN></I><SPAN STYLE="font-weight: normal"> is invalid or </SPAN><I><SPAN STYLE="font-weight: normal">type</SPAN></I><SPAN STYLE="font-weight: normal"> is none of:</SPAN></DT><DL> <DL> <DT> <B>PTHREAD_MUTEX_NORMAL<BR>PTHREAD_MUTEX_FAST_NP<BR>PTHREAD_MUTEX_RECURSIVE<BR>PTHREAD_MUTEX_RECURSIVE_NP<BR>PTHREAD_MUTEX_ERRORCHECK<BR>PTHREAD_MUTEX_ERRORCHECK_NP</B></DT></DL> </DL> </DL> </DL> <DD STYLE="margin-left: 0in"> <BR> </DD></DL> <P> <B>pthread_mutexattr_getrobust</B></P> <P STYLE="margin-left: 0.79in"><B>EINVAL</B><SPAN STYLE="font-weight: normal"> – </SPAN><I><SPAN STYLE="font-weight: normal">attr</SPAN></I><SPAN STYLE="font-weight: normal"> or </SPAN><I><SPAN STYLE="font-weight: normal">robust</SPAN></I><SPAN STYLE="font-weight: normal"> is invalid.</SPAN></P> <P><B>pthread_mutexattr_setrobust</B></P> <P STYLE="margin-left: 0.79in"><B>EINVAL</B><SPAN STYLE="font-weight: normal"> – </SPAN><I><SPAN STYLE="font-weight: normal">attr</SPAN></I><SPAN STYLE="font-weight: normal"> or </SPAN><I><SPAN STYLE="font-weight: normal">robust</SPAN></I><SPAN STYLE="font-weight: normal"> is invalid.</SPAN></P> <H2 CLASS="western"><A HREF="#toc5" NAME="sect5">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> <H2 CLASS="western"><A HREF="#toc6" NAME="sect6">See Also</A></H2> <P><A HREF="pthread_mutex_init.html"><B>pthread_mutex_init</B>(3)</A> , <A HREF="pthread_mutex_lock.html"><B>pthread_mutex_lock</B>(3)</A> , <A HREF="pthread_mutex_unlock.html"><B>pthread_mutex_unlock</B>(3)</A> . </P> <H2 CLASS="western"><A HREF="#toc7" NAME="sect7"><FONT COLOR="#000080"><U>Notes</U></FONT></A></H2> <P>For speed, <B>Pthreads-w32</B> never checks the thread ownership of non-robust mutexes of type <B>PTHREAD_MUTEX_NORMAL</B> (or <B>PTHREAD_MUTEX_FAST_NP</B>) when performing operations on the mutex. It is therefore possible for one thread to lock such a mutex and another to unlock it.</P> <P STYLE="font-weight: normal">When developing code, it is a common precaution to substitute the error checking type, then drop in the normal type for release if the extra performance is required.</P> <HR> <P><A NAME="toc"></A><B>Table of Contents</B></P> <UL> <LI><P STYLE="margin-bottom: 0in"><A HREF="#sect0" NAME="toc0">Name</A> </P> <LI><P STYLE="margin-bottom: 0in"><A HREF="#sect1" NAME="toc1">Synopsis</A> </P> <LI><P STYLE="margin-bottom: 0in"><A HREF="#sect2" NAME="toc2">Description</A> </P> <LI><P STYLE="margin-bottom: 0in"><A HREF="#sect3" NAME="toc3">Return Value</A> </P> <LI><P STYLE="margin-bottom: 0in"><A HREF="#sect5" NAME="toc5">Author</A> </P> <LI><P STYLE="margin-bottom: 0in"><A HREF="#sect6" NAME="toc6">See Also</A></P> <LI><P><A HREF="#sect7" NAME="toc7">Notes</A></P> </UL> </BODY> </HTML>