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<TITLE>PTHREAD_MUTEXATTR(3) manual page</TITLE>
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<H4 CLASS="western">POSIX Threads for Windows – REFERENCE -
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<A HREF="http://sources.redhat.com/pthreads-win32">Pthreads-w32</A></H4>
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<P><A HREF="index.html">Reference Index</A></P>
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<P><A HREF="#toc">Table of Contents</A></P>
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<H2 CLASS="western"><A HREF="#toc0" NAME="sect0">Name</A></H2>
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<P>pthread_mutexattr_init, pthread_mutexattr_destroy,
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pthread_mutexattr_settype, pthread_mutexattr_gettype - mutex creation
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attributes
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</P>
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<H2 CLASS="western"><A HREF="#toc1" NAME="sect1">Synopsis</A></H2>
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<P><B>#include <pthread.h></B>
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</P>
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<P><B>int pthread_mutexattr_init(pthread_mutexattr_t *</B><I>attr</I><B>);</B>
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</P>
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<P><B>int pthread_mutexattr_destroy(pthread_mutexattr_t *</B><I>attr</I><B>);</B>
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</P>
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<P><B>int pthread_mutexattr_settype(pthread_mutexattr_t *</B><I>attr</I><B>,
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int </B><I>type</I><B>);</B>
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</P>
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<P><B>int pthread_mutexattr_gettype(const pthread_mutexattr_t *</B><I>attr</I><B>,
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int *</B><I>type</I><B>);</B>
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</P>
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<P><B>int pthread_mutexattr_setkind_np(pthread_mutexattr_t *</B><I>attr</I><B>,
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int </B><I>type</I><B>);</B>
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</P>
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<P><B>int pthread_mutexattr_getkind_np(const pthread_mutexattr_t
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*</B><I>attr</I><B>, int *</B><I>type</I><B>);</B>
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</P>
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<P><B>int pthread_mutexattr_setrobust(pthread_mutexattr_t *</B><I>attr</I><B>,
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int</B><SPAN STYLE="font-weight: normal"> </SPAN><I><SPAN STYLE="font-weight: normal">robust</SPAN></I><B>);</B>
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</P>
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<P><B>int pthread_mutexattr_getrobust(pthread_mutexattr_t *</B><I>attr</I><B>,
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int</B><SPAN STYLE="font-weight: normal"> </SPAN><B>*</B><I><SPAN STYLE="font-weight: normal">robust</SPAN></I><B>);</B>
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</P>
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<H2 CLASS="western"><A HREF="#toc2" NAME="sect2">Description</A></H2>
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<P>Mutex attributes can be specified at mutex creation time, by
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passing a mutex attribute object as second argument to
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<A HREF="pthread_mutex_init.html"><B>pthread_mutex_init</B>(3)</A> .
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Passing <B>NULL</B> is equivalent to passing a mutex attribute object
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with all attributes set to their default values.
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</P>
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<P><B>pthread_mutexattr_init</B> initializes the mutex attribute
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object <I>attr</I> and fills it with default values for the
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attributes.
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</P>
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<P><B>pthread_mutexattr_destroy</B> destroys a mutex attribute
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object, which must not be reused until it is reinitialized.</P>
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<P><B>pthread_mutexattr_settype</B> sets the mutex type attribute in
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<I>attr</I> to the value specified by <I>type</I>.
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</P>
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<P><B>pthread_mutexattr_gettype</B> retrieves the current value of
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the mutex kind attribute in <I>attr</I> and stores it in the location
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pointed to by <I>type</I>.
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</P>
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<P><B>Pthreads-w32</B> also recognises the following equivalent
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functions that are used in Linux:</P>
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<P><B>pthread_mutexattr_setkind_np</B> is an alias for
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<B>pthread_mutexattr_settype</B>.
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</P>
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<P STYLE="font-weight: normal"><B>pthread_mutexattr_getkind_np</B> is
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an alias for <B>pthread_mutexattr_gettype</B>.
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</P>
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<P>The following mutex types are supported:</P>
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<P STYLE="margin-left: 0.79in"><B>PTHREAD_MUTEX_NORMAL</B> - for
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‘‘fast’’ mutexes.</P>
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<P STYLE="margin-left: 0.79in"><B>PTHREAD_MUTEX_RECURSIVE</B> - for
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‘‘recursive’’ mutexes.</P>
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<P STYLE="margin-left: 0.79in"><B>PTHREAD_MUTEX_ERRORCHECK</B> - for
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‘‘error checking’’ mutexes.</P>
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<P>The mutex type determines what happens if a thread attempts to
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lock a mutex it already owns with <A HREF="pthread_mutex_lock.html"><B>pthread_mutex_lock</B>(3)</A>
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. If the mutex is of the “normal” or “fast” type,
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<A HREF="pthread_mutex_lock.html"><B>pthread_mutex_lock</B>(3)</A>
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simply suspends the calling thread forever. If the mutex is of the
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‘‘error checking’’ type, <A HREF="pthread_mutex_lock.html"><B>pthread_mutex_lock</B>(3)</A>
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returns immediately with the error code <B>EDEADLK</B>. If the mutex
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is of the ‘‘recursive’’ type, the call to
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<A HREF="pthread_mutex_lock.html"><B>pthread_mutex_lock</B>(3)</A>
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returns immediately with a success return code. The number of times
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the thread owning the mutex has locked it is recorded in the mutex.
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The owning thread must call <A HREF="pthread_mutex_unlock.html"><B>pthread_mutex_unlock</B>(3)</A>
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the same number of times before the mutex returns to the unlocked
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state.
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</P>
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<P>The default mutex type is <B>PTHREAD_MUTEX_NORMAL</B></P>
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<P><B>Pthreads-w32</B> also recognises the following equivalent types
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that are used by Linux:</P>
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<P STYLE="margin-left: 0.79in; font-weight: normal"><B>PTHREAD_MUTEX_FAST_NP</B>
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– equivalent to <B>PTHREAD_MUTEX_NORMAL</B></P>
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<P STYLE="margin-left: 0.79in"><B>PTHREAD_MUTEX_RECURSIVE_NP</B></P>
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<P STYLE="margin-left: 0.79in"><B>PTHREAD_MUTEX_ERRORCHECK_NP</B></P>
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<P><B>pthread_mutexattr_setrobust</B><SPAN STYLE="font-weight: normal">
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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>
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<P><B>pthread_mutexattr_getrobust</B><SPAN STYLE="font-weight: normal">
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returns the current robustness value to the location given by
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*</SPAN><I><SPAN STYLE="font-weight: normal">robust</SPAN></I><SPAN STYLE="font-weight: normal">.</SPAN></P>
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<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">
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are:</SPAN></P>
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<P STYLE="margin-left: 0.79in"><B>PTHREAD_MUTEX_STALLED</B><SPAN STYLE="font-weight: normal">
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- when the owner of the mutex terminates without unlocking the mutex,
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all subsequent calls
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to pthread_mutex_*lock() are blocked from
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progress in an unspecified manner.</SPAN></P>
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<P STYLE="margin-left: 0.79in"><B>PTHREAD_MUTEX_ROBUST</B><SPAN STYLE="font-weight: normal">
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- when the owner of the mutex terminates without unlocking the mutex,
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the mutex is
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unlocked. The next owner of this mutex acquires the
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mutex with an error return of
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EOWNERDEAD.</SPAN></P>
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<H2 CLASS="western"><A HREF="#toc3" NAME="sect3">Return Value</A></H2>
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<P><SPAN STYLE="font-weight: normal">On success all functions return
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0, otherwise they return an error code as follows:</SPAN></P>
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<P><B>pthread_mutexattr_init</B></P>
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<P STYLE="margin-left: 0.79in"><B>ENOMEM</B><SPAN STYLE="font-weight: normal">
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- insufficient memory for </SPAN><I><SPAN STYLE="font-weight: normal">attr</SPAN></I><SPAN STYLE="font-weight: normal">.</SPAN></P>
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<P><B>pthread_mutexattr_destroy</B></P>
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<P STYLE="margin-left: 0.79in"><B>EINVAL</B><SPAN STYLE="font-weight: normal">
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- </SPAN><I><SPAN STYLE="font-weight: normal">attr</SPAN></I><SPAN STYLE="font-weight: normal">
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is invalid.</SPAN></P>
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<P><B>pthread_mutexattr_gettype</B></P>
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<P STYLE="margin-left: 0.79in"><B>EINVAL</B><SPAN STYLE="font-weight: normal">
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- </SPAN><I><SPAN STYLE="font-weight: normal">attr</SPAN></I><SPAN STYLE="font-weight: normal">
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is invalid.</SPAN></P>
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<P><B>pthread_mutexattr_settype</B></P>
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<DL>
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<DL>
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<DL>
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<DT><B>EINVAL</B><SPAN STYLE="font-weight: normal"> - </SPAN><I><SPAN STYLE="font-weight: normal">attr</SPAN></I><SPAN STYLE="font-weight: normal">
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is invalid or </SPAN><I><SPAN STYLE="font-weight: normal">type</SPAN></I><SPAN STYLE="font-weight: normal">
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is none of:</SPAN></DT><DL>
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<DL>
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<DT>
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<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>
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</DL>
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</DL>
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</DL>
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<DD STYLE="margin-left: 0in">
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<BR>
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</DD></DL>
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<P>
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<B>pthread_mutexattr_getrobust</B></P>
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<P STYLE="margin-left: 0.79in"><B>EINVAL</B><SPAN STYLE="font-weight: normal">
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– </SPAN><I><SPAN STYLE="font-weight: normal">attr</SPAN></I><SPAN STYLE="font-weight: normal">
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or </SPAN><I><SPAN STYLE="font-weight: normal">robust</SPAN></I><SPAN STYLE="font-weight: normal">
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is invalid.</SPAN></P>
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<P><B>pthread_mutexattr_setrobust</B></P>
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<P STYLE="margin-left: 0.79in"><B>EINVAL</B><SPAN STYLE="font-weight: normal">
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– </SPAN><I><SPAN STYLE="font-weight: normal">attr</SPAN></I><SPAN STYLE="font-weight: normal">
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or </SPAN><I><SPAN STYLE="font-weight: normal">robust</SPAN></I><SPAN STYLE="font-weight: normal">
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is invalid.</SPAN></P>
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<H2 CLASS="western"><A HREF="#toc5" NAME="sect5">Author</A></H2>
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<P>Xavier Leroy <Xavier.Leroy@inria.fr>
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</P>
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<P>Modified by Ross Johnson for use with <A HREF="http://sources.redhat.com/pthreads-win32">Pthreads-w32</A>.</P>
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<H2 CLASS="western"><A HREF="#toc6" NAME="sect6">See Also</A></H2>
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<P><A HREF="pthread_mutex_init.html"><B>pthread_mutex_init</B>(3)</A>
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, <A HREF="pthread_mutex_lock.html"><B>pthread_mutex_lock</B>(3)</A>
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, <A HREF="pthread_mutex_unlock.html"><B>pthread_mutex_unlock</B>(3)</A>
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.
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</P>
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<H2 CLASS="western"><A HREF="#toc7" NAME="sect7"><FONT COLOR="#000080"><U>Notes</U></FONT></A></H2>
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<P>For speed, <B>Pthreads-w32</B> never checks the thread ownership
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of non-robust mutexes of type <B>PTHREAD_MUTEX_NORMAL</B> (or
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<B>PTHREAD_MUTEX_FAST_NP</B>) when performing operations on the
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mutex. It is therefore possible for one thread to lock such a mutex
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and another to unlock it.</P>
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<P STYLE="font-weight: normal">When developing code, it is a common
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precaution to substitute the error checking type, then drop in the
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normal type for release if the extra performance is required.</P>
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<HR>
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<P><A NAME="toc"></A><B>Table of Contents</B></P>
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<UL>
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<LI><P STYLE="margin-bottom: 0in"><A HREF="#sect0" NAME="toc0">Name</A>
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</P>
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<LI><P STYLE="margin-bottom: 0in"><A HREF="#sect1" NAME="toc1">Synopsis</A>
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</P>
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<LI><P STYLE="margin-bottom: 0in"><A HREF="#sect2" NAME="toc2">Description</A>
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</P>
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<LI><P STYLE="margin-bottom: 0in"><A HREF="#sect3" NAME="toc3">Return
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Value</A>
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</P>
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<LI><P STYLE="margin-bottom: 0in"><A HREF="#sect5" NAME="toc5">Author</A>
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</P>
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<LI><P STYLE="margin-bottom: 0in"><A HREF="#sect6" NAME="toc6">See
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Also</A></P>
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<LI><P><A HREF="#sect7" NAME="toc7">Notes</A></P>
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</UL>
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