187 lines
4.5 KiB
HTML
187 lines
4.5 KiB
HTML
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<HTML><HEAD><TITLE>Man page of SEM_INIT</TITLE>
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</HEAD><BODY>
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<H1>SEM_INIT</H1>
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Section: Linux Programmer's Manual (3)<BR>Updated: 2017-09-15<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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sem_init - initialize an unnamed semaphore
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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/semaphore.h">semaphore.h</A>></B>
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<B>int sem_init(sem_t *</B><I>sem</I><B>, int </B><I>pshared</I><B>, unsigned int </B><I>value</I><B>);</B>
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</PRE>
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<P>
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Link with <I>-pthread</I>.
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<A NAME="lbAD"> </A>
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<H2>DESCRIPTION</H2>
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<B>sem_init</B>()
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initializes the unnamed semaphore at the address pointed to by
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<I>sem</I>.
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The
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<I>value</I>
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argument specifies the initial value for the semaphore.
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<P>
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The
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<I>pshared</I>
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argument indicates whether this semaphore is to be shared
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between the threads of a process, or between processes.
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<P>
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If
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<I>pshared</I>
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has the value 0,
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then the semaphore is shared between the threads of a process,
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and should be located at some address that is visible to all threads
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(e.g., a global variable, or a variable allocated dynamically on
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the heap).
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<P>
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If
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<I>pshared</I>
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is nonzero, then the semaphore is shared between processes,
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and should be located in a region of shared memory (see
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<B><A HREF="/cgi-bin/man/man2html?3+shm_open">shm_open</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?2+mmap">mmap</A></B>(2),
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and
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<B><A HREF="/cgi-bin/man/man2html?2+shmget">shmget</A></B>(2)).
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(Since a child created by
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<B><A HREF="/cgi-bin/man/man2html?2+fork">fork</A></B>(2)
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inherits its parent's memory mappings, it can also access the semaphore.)
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Any process that can access the shared memory region
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can operate on the semaphore using
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<B><A HREF="/cgi-bin/man/man2html?3+sem_post">sem_post</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+sem_wait">sem_wait</A></B>(3),
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and so on.
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<P>
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Initializing a semaphore that has already been initialized
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results in undefined behavior.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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<B>sem_init</B>()
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returns 0 on success;
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on error, -1 is returned, and
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<I>errno</I>
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is set to indicate the error.
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<A NAME="lbAF"> </A>
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<H2>ERRORS</H2>
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<DL COMPACT>
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<DT id="1"><B>EINVAL</B>
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<DD>
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<I>value</I>
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exceeds
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<B>SEM_VALUE_MAX</B>.
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<DT id="2"><B>ENOSYS</B>
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<DD>
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<I>pshared</I>
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is nonzero,
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but the system does not support process-shared semaphores (see
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<B><A HREF="/cgi-bin/man/man2html?7+sem_overview">sem_overview</A></B>(7)).
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</DL>
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<A NAME="lbAG"> </A>
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<H2>ATTRIBUTES</H2>
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For an explanation of the terms used in this section, see
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<B><A HREF="/cgi-bin/man/man2html?7+attributes">attributes</A></B>(7).
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<TABLE BORDER>
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<TR VALIGN=top><TD><B>Interface</B></TD><TD><B>Attribute</B></TD><TD><B>Value</B><BR></TD></TR>
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<TR VALIGN=top><TD>
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<B>sem_init</B>()
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</TD><TD>Thread safety</TD><TD>MT-Safe<BR></TD></TR>
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</TABLE>
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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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<A NAME="lbAI"> </A>
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<H2>NOTES</H2>
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Bizarrely, POSIX.1-2001 does not specify the value that should
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be returned by a successful call to
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<B>sem_init</B>().
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POSIX.1-2008 rectifies this, specifying the zero return on success.
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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+sem_destroy">sem_destroy</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+sem_post">sem_post</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?3+sem_wait">sem_wait</A></B>(3),
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<B><A HREF="/cgi-bin/man/man2html?7+sem_overview">sem_overview</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="3"><A HREF="#lbAB">NAME</A><DD>
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<DT id="4"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="5"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="6"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="7"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="8"><A HREF="#lbAG">ATTRIBUTES</A><DD>
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<DT id="9"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="10"><A HREF="#lbAI">NOTES</A><DD>
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<DT id="11"><A HREF="#lbAJ">SEE ALSO</A><DD>
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<DT id="12"><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: 00:05:56 GMT, March 31, 2021
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