141 lines
3.4 KiB
HTML
141 lines
3.4 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_GETVALUE</TITLE>
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</HEAD><BODY>
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<H1>SEM_GETVALUE</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_getvalue - get the value of a 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_getvalue(sem_t *</B><I>sem</I><B>, int *</B><I>sval</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_getvalue</B>()
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places the current value of the semaphore pointed to
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<I>sem</I>
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into the integer pointed to by
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<I>sval</I>.
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<P>
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If one or more processes or threads are blocked
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waiting to lock the semaphore with
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<B><A HREF="/cgi-bin/man/man2html?3+sem_wait">sem_wait</A></B>(3),
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POSIX.1 permits two possibilities for the value returned in
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<I>sval</I>:
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either 0 is returned;
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or a negative number whose absolute value is the count
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of the number of processes and threads currently blocked in
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<B><A HREF="/cgi-bin/man/man2html?3+sem_wait">sem_wait</A></B>(3).
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Linux adopts the former behavior.
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<A NAME="lbAE"> </A>
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<H2>RETURN VALUE</H2>
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<B>sem_getvalue</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>sem</I>
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is not a valid semaphore.
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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_getvalue</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, POSIX.1-2008.
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<A NAME="lbAI"> </A>
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<H2>NOTES</H2>
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The value of the semaphore may already have changed by the time
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<B>sem_getvalue</B>()
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returns.
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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_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="2"><A HREF="#lbAB">NAME</A><DD>
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<DT id="3"><A HREF="#lbAC">SYNOPSIS</A><DD>
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<DT id="4"><A HREF="#lbAD">DESCRIPTION</A><DD>
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<DT id="5"><A HREF="#lbAE">RETURN VALUE</A><DD>
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<DT id="6"><A HREF="#lbAF">ERRORS</A><DD>
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<DT id="7"><A HREF="#lbAG">ATTRIBUTES</A><DD>
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<DT id="8"><A HREF="#lbAH">CONFORMING TO</A><DD>
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<DT id="9"><A HREF="#lbAI">NOTES</A><DD>
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<DT id="10"><A HREF="#lbAJ">SEE ALSO</A><DD>
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<DT id="11"><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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