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193 lines
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<TITLE>"PTHREAD_RWLOCK_DESTROY"(P) manual page</TITLE>
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<BODY LANG="en-GB" BGCOLOR="#ffffff" DIR="LTR">
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<H4>POSIX Threads for Windows – REFERENCE - <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><A HREF="#toc0" NAME="sect0">Name</A></H2>
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<P>pthread_rwlock_destroy, pthread_rwlock_init - destroy and
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initialize a read-write lock object
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</P>
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<H2><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>pthread_wrlock_t </B><I>rwlock</I> <B>=
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PTHREAD_RWLOCK_INITIALIZER;</B></P>
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<P><B>int pthread_rwlock_destroy(pthread_rwlock_t *</B><I>rwlock</I><B>);
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<BR>int pthread_rwlock_init(pthread_rwlock_t *restrict</B> <I>rwlock</I><B>,
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const pthread_rwlockattr_t *restrict</B> <I>attr</I><B>); </B>
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</P>
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<H2><A HREF="#toc2" NAME="sect2">Description</A></H2>
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<P>The <B>pthread_rwlock_destroy</B> function shall destroy the
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read-write lock object referenced by <I>rwlock</I> and release any
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resources used by the lock. The effect of subsequent use of the lock
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is undefined until the lock is reinitialized by another call to
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<B>pthread_rwlock_init</B>. An implementation may cause
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<B>pthread_rwlock_destroy</B> to set the object referenced by <I>rwlock</I>
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to an invalid value. Results are undefined if <B>pthread_rwlock_destroy</B>
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is called when any thread holds <I>rwlock</I>. Attempting to destroy
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an uninitialized read-write lock results in undefined behavior.
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</P>
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<P>The <B>pthread_rwlock_init</B> function shall allocate any
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resources required to use the read-write lock referenced by <I>rwlock</I>
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and initializes the lock to an unlocked state with attributes
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referenced by <I>attr</I>. If <I>attr</I> is NULL, the default
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read-write lock attributes shall be used; the effect is the same as
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passing the address of a default read-write lock attributes object.
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Once initialized, the lock can be used any number of times without
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being reinitialized. Results are undefined if <B>pthread_rwlock_init</B>
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is called specifying an already initialized read-write lock. Results
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are undefined if a read-write lock is used without first being
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initialized.
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</P>
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<P>If the <B>pthread_rwlock_init</B> function fails, <I>rwlock</I>
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shall not be initialized and the contents of <I>rwlock</I> are
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undefined.
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</P>
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<P><B>Pthreads-w32</B> supports statically initialized <I>rwlock</I>
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objects using <B>PTHREAD_RWLOCK_INITIALIZER</B>. <SPAN STYLE="font-weight: medium">
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An application should still call <B>pthread_rwlock_destroy</B> at
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some point to ensure that any resources consumed by the read/write
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lock are released.</SPAN></P>
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<P>Only the object referenced by <I>rwlock</I> may be used for
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performing synchronization. The result of referring to copies of that
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object in calls to <B>pthread_rwlock_destroy</B> ,
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<B>pthread_rwlock_rdlock</B> , <B>pthread_rwlock_timedrdlock</B> ,
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<B>pthread_rwlock_timedwrlock</B> , <B>pthread_rwlock_tryrdlock</B> ,
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<B>pthread_rwlock_trywrlock</B> , <B>pthread_rwlock_unlock</B> , or
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<B>pthread_rwlock_wrlock</B> is undefined.
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</P>
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<P><B>Pthreads-w32</B> defines <B>_POSIX_READER_WRITER_LOCKS</B> in
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pthread.h as 200112L to indicate that the reader/writer routines are
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implemented and may be used.</P>
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<H2><A HREF="#toc3" NAME="sect3">Return Value</A></H2>
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<P>If successful, the <B>pthread_rwlock_destroy</B> and
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<B>pthread_rwlock_init</B> functions shall return zero; otherwise, an
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error number shall be returned to indicate the error.
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</P>
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<P>The [EBUSY] and [EINVAL] error checks, if implemented, act as if
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they were performed immediately at the beginning of processing for
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the function and caused an error return prior to modifying the state
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of the read-write lock specified by <I>rwlock</I>.
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</P>
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<H2><A HREF="#toc4" NAME="sect4">Errors</A></H2>
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<P>The <B>pthread_rwlock_destroy</B> function may fail if:
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</P>
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<DL>
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<DT><B>EBUSY</B>
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</DT><DD>
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The implementation has detected an attempt to destroy the object
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referenced by <I>rwlock</I> while it is locked.
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</DD><DT>
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<B>EINVAL</B>
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</DT><DD STYLE="margin-bottom: 0.5cm">
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The value specified by <I>rwlock</I> is invalid.
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</DD></DL>
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<P>
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The <B>pthread_rwlock_init</B> function shall fail if:
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</P>
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<DL>
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<DT><B>EAGAIN</B>
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</DT><DD>
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The system lacked the necessary resources (other than memory) to
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initialize another read-write lock.
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</DD><DT>
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<B>ENOMEM</B>
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</DT><DD>
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Insufficient memory exists to initialize the read-write lock.
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</DD><DD STYLE="margin-left: 0cm; margin-bottom: 0.5cm">
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<BR><BR>
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</DD></DL>
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<P>
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The <B>pthread_rwlock_init</B> function may fail if:
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</P>
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<DL>
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<DT><B>EINVAL</B>
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</DT><DD STYLE="margin-bottom: 0.5cm">
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The value specified by <I>attr</I> is invalid.
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</DD></DL>
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<P>
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These functions shall not return an error code of [EINTR].
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</P>
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<P><I>The following sections are informative.</I>
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</P>
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<H2><A HREF="#toc5" NAME="sect5">Examples</A></H2>
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<P>None.
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</P>
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<H2><A HREF="#toc6" NAME="sect6">Application Usage</A></H2>
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<P>Applications using these and related read-write lock functions may
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be subject to priority inversion, as discussed in the Base
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Definitions volume of IEEE Std 1003.1-2001, Section 3.285,
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Priority Inversion.
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</P>
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<H2><A HREF="#toc7" NAME="sect7">Rationale</A></H2>
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<P>None.
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</P>
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<H2><A HREF="#toc8" NAME="sect8">Future Directions</A></H2>
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<P>None.
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</P>
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<H2><A HREF="#toc9" NAME="sect9">See Also</A></H2>
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<P><A HREF="pthread_rwlock_rdlock.html"><B>pthread_rwlock_rdlock</B>(3)</A>
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<B>,</B> <A HREF="pthread_rwlock_timedrdlock.html"><B>pthread_rwlock_timedrdlock</B>(3)</A>
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<B>,</B> <A HREF="pthread_rwlock_timedwrlock.html"><B>pthread_rwlock_timedwrlock</B>(3)</A>
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<B>,</B> <A HREF="pthread_rwlock_rdlock.html"><B>pthread_rwlock_tryrdlock</B>(3)</A>
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<B>,</B> <A HREF="pthread_rwlock_wrlock.html"><B>pthread_rwlock_trywrlock</B>(3)</A>
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<B>,</B> <A HREF="pthread_rwlock_unlock.html"><B>pthread_rwlock_unlock</B>(3)</A>
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<B>,</B> <A HREF="pthread_rwlock_wrlock.html"><B>pthread_rwlock_wrlock</B>(3)</A>
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<B>,</B> the Base Definitions volume of IEEE Std 1003.1-2001,
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<I><pthread.h></I>
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</P>
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<H2><A HREF="#toc10" NAME="sect10">Copyright</A></H2>
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<P>Portions of this text are reprinted and reproduced in electronic
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form from IEEE Std 1003.1, 2003 Edition, Standard for Information
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Technology -- Portable Operating System Interface (POSIX), The Open
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Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the
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Institute of Electrical and Electronics Engineers, Inc and The Open
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Group. In the event of any discrepancy between this version and the
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original IEEE and The Open Group Standard, the original IEEE and The
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Open Group Standard is the referee document. The original Standard
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can be obtained online at <A HREF="http://www.opengroup.org/unix/online.html">http://www.opengroup.org/unix/online.html</A>
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.
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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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<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: 0cm"><A HREF="#sect0" NAME="toc0">Name</A>
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</P>
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<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect1" NAME="toc1">Synopsis</A>
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</P>
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<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect2" NAME="toc2">Description</A>
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</P>
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<LI><P STYLE="margin-bottom: 0cm"><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: 0cm"><A HREF="#sect4" NAME="toc4">Errors</A>
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</P>
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<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect5" NAME="toc5">Examples</A>
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</P>
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<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect6" NAME="toc6">Application
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Usage</A>
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</P>
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<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect7" NAME="toc7">Rationale</A>
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</P>
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<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect8" NAME="toc8">Future
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Directions</A>
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</P>
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<LI><P STYLE="margin-bottom: 0cm"><A HREF="#sect9" NAME="toc9">See
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Also</A>
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</P>
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<LI><P><A HREF="#sect10" NAME="toc10">Copyright</A>
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</P>
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</UL>
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