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255 lines
6.2 KiB
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of PTHREAD_SPIN_INIT</TITLE>
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</HEAD><BODY>
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<H1>PTHREAD_SPIN_INIT</H1>
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Section: Linux Programmer's Manual (3)<BR>Updated: 2017-09-30<BR><A HREF="#index">Index</A>
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<A HREF="/cgi-bin/man/man2html">Return to Main Contents</A><HR>
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<A NAME="lbAB"> </A>
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<H2>NAME</H2>
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pthread_spin_init, pthread_spin_destroy - initialize or destroy a spin lock
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<A NAME="lbAC"> </A>
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<H2>SYNOPSIS</H2>
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<PRE>
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<B>#include <<A HREF="file:///usr/include/pthread.h">pthread.h</A>></B>
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<B>int pthread_spin_init(pthread_spinlock_t *</B><I>lock</I><B>, int </B><I>pshared</I><B>);</B>
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<B>int pthread_spin_destroy(pthread_spinlock_t *</B><I>lock</I><B>);</B>
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</PRE>
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<P>
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Compile and link with <I>-pthread</I>.
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<P>
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Feature Test Macro Requirements for glibc (see
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<B><A HREF="/cgi-bin/man/man2html?7+feature_test_macros">feature_test_macros</A></B>(7)):
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<P>
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<B>pthread_spin_init</B>(),
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<B>pthread_spin_destroy</B>():
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<BR>
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<DL COMPACT><DT id="1"><DD>
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_POSIX_C_SOURCE >= 200112L
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</DL>
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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<I>General note</I>:
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Most programs should use mutexes
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instead of spin locks.
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Spin locks are primarily useful in conjunction with real-time
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scheduling policies.
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See NOTES.
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<P>
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The
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<B>pthread_spin_init</B>()
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function allocates any resources required for the use of
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the spin lock referred to by
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<I>lock</I>
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and initializes the lock to be in the unlocked state.
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The
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<I>pshared</I>
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argument must have one of the following values:
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<DL COMPACT>
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<DT id="2"><B>PTHREAD_PROCESS_PRIVATE</B>
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<DD>
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The spin lock is to be operated on only by threads in the same process
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as the thread that calls
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<B>pthread_spin_init</B>().
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(Attempting to share the spin lock between processes
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results in undefined behavior.)
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<DT id="3"><B>PTHREAD_PROCESS_SHARED</B>
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<DD>
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The spin lock may be operated on by any thread in any process that
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has access to the memory containing the lock
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(i.e., the lock may be in a shared memory object that is
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shared among multiple processes).
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</DL>
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<P>
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Calling
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<B>pthread_spin_init</B>()
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on a spin lock that has already been initialized results
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in undefined behavior.
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<P>
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The
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<B>pthread_spin_destroy</B>()
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function destroys a previously initialized spin lock,
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freeing any resources that were allocated for that lock.
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Destroying a spin lock that has not been previously been initialized
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or destroying a spin lock while another thread holds the lock
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results in undefined behavior.
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<P>
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Once a spin lock has been destroyed,
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performing any operation on the lock other than
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once more initializing it with
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<B>pthread_spin_init</B>()
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results in undefined behavior.
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<P>
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The result of performing operations such as
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_spin_lock">pthread_spin_lock</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_spin_unlock">pthread_spin_unlock</A></B>(3),
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and
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_spin_destroy">pthread_spin_destroy</A></B>(3)
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on
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<I>copies</I>
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of the object referred to by
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<I>lock</I>
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is undefined.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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On success, there functions return zero.
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On failure, they return an error number.
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In the event that
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<B>pthread_spin_init</B>()
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fails, the lock is not initialized.
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<A NAME="lbAF"> </A>
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<H2>ERRORS</H2>
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<B>pthread_spin_init</B>()
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may fail with the following errors:
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<DL COMPACT>
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<DT id="4"><B>EAGAIN</B>
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<DD>
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The system has insufficient resources to initialize
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a new spin lock.
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<DT id="5"><B>ENOMEM</B>
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<DD>
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Insufficient memory to initialize the spin lock.
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</DL>
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<A NAME="lbAG"> </A>
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<H2>VERSIONS</H2>
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These functions first appeared in glibc in version 2.2.
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<A NAME="lbAH"> </A>
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<H2>CONFORMING TO</H2>
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POSIX.1-2001.
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<P>
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Support for process-shared spin locks is a POSIX option.
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The option is supported in the glibc implementation.
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<A NAME="lbAI"> </A>
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<H2>NOTES</H2>
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Spin locks should be employed in conjunction with
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real-time scheduling policies
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(<B>SCHED_FIFO</B>,
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or possibly
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<B>SCHED_RR</B>).
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Use of spin locks with nondeterministic scheduling policies such as
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<B>SCHED_OTHER</B>
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probably indicates a design mistake.
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The problem is that if a thread operating under such a policy
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is scheduled off the CPU while it holds a spin lock,
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then other threads will waste time spinning on the lock
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until the lock holder is once more rescheduled and releases the lock.
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<P>
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If threads create a deadlock situation while employing spin locks,
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those threads will spin forever consuming CPU time.
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<P>
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User-space spin locks are
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<I>not</I>
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applicable as a general locking solution.
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They are, by definition,
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prone to priority inversion and unbounded spin times.
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A programmer using spin locks must be exceptionally careful not
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only in the code, but also in terms of system configuration,
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thread placement, and priority assignment.
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<A NAME="lbAJ"> </A>
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<H2>SEE ALSO</H2>
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_mutex_init">pthread_mutex_init</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_mutex_lock">pthread_mutex_lock</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_spin_lock">pthread_spin_lock</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+pthread_spin_unlock">pthread_spin_unlock</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?7+pthreads">pthreads</A></B>(7)
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<A NAME="lbAK"> </A>
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<H2>COLOPHON</H2>
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This page is part of release 5.05 of the Linux
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<I>man-pages</I>
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project.
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A description of the project,
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information about reporting bugs,
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and the latest version of this page,
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can be found at
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<A HREF="https://www.kernel.org/doc/man-pages/.">https://www.kernel.org/doc/man-pages/.</A>
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<P>
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<HR>
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<A NAME="index"> </A><H2>Index</H2>
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<DL>
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<DT id="6"><A HREF="#lbAB">NAME</A><DD>
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<DT id="7"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="8"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="9"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="10"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="11"><A HREF="#lbAG">VERSIONS</A><DD>
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<DT id="12"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="13"><A HREF="#lbAI">NOTES</A><DD>
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<DT id="14"><A HREF="#lbAJ">SEE ALSO</A><DD>
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<DT id="15"><A HREF="#lbAK">COLOPHON</A><DD>
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</DL>
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<HR>
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This document was created by
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<A HREF="/cgi-bin/man/man2html">man2html</A>,
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using the manual pages.<BR>
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Time: 00:05:53 GMT, March 31, 2021
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