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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2003 The Open Group, All Rights Reserved --><title>semctl</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="semctl"></a> <a name="tag_03_638"></a><!-- semctl --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2003 Edition<br>Copyright © 2001-2003 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_03_638_01"></a>NAME</h4><blockquote>semctl - XSI semaphore control operations</blockquote><h4><a name="tag_03_638_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><div class="box"><code><tt><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> #include <sys/sem.h><br><br> int semctl(int</tt> <i>semid</i><tt>, int</tt> <i>semnum</i><tt>, int</tt> <i>cmd</i><tt>, ...); <img src="../images/opt-end.gif"alt="[Option End]" border="0"></tt></code></div><tt><br></tt></blockquote><h4><a name="tag_03_638_03"></a>DESCRIPTION</h4><blockquote><p>The <i>semctl</i>() function operates on XSI semaphores (see the Base Definitions volume of IEEE Std 1003.1-2001, <ahref="../basedefs/xbd_chap04.html#tag_04_15">Section 4.15, Semaphore</a>). It is unspecified whether this function interoperateswith the realtime interprocess communication facilities defined in <a href="xsh_chap02_08.html#tag_02_08"><i>Realtime</i></a> .</p><p>The <i>semctl</i>() function provides a variety of semaphore control operations as specified by <i>cmd</i>. The fourth argumentis optional and depends upon the operation requested. If required, it is of type <b>union semun</b>, which the application shallexplicitly declare:</p><pre><tt>union semun { int val; struct semid_ds *buf; unsigned short *array;} arg;</tt></pre><p>The following semaphore control operations as specified by <i>cmd</i> are executed with respect to the semaphore specified by<i>semid</i> and <i>semnum</i>. The level of permission required for each operation is shown with each command; see <a href="xsh_chap02_07.html#tag_02_07"><i>XSI Interprocess Communication</i></a> . The symbolic names for the values of <i>cmd</i> aredefined in the <a href="../basedefs/sys/sem.h.html"><i><sys/sem.h></i></a> header:</p><dl compact><dt>GETVAL</dt><dd>Return the value of <i>semval</i>; see <a href="../basedefs/sys/sem.h.html"><i><sys/sem.h></i></a>. Requires readpermission.</dd><dt>SETVAL</dt><dd>Set the value of <i>semval</i> to <i>arg.val</i>, where <i>arg</i> is the value of the fourth argument to <i>semctl</i>(). Whenthis command is successfully executed, the <i>semadj</i> value corresponding to the specified semaphore in all processes iscleared. Requires alter permission; see <a href="xsh_chap02_07.html#tag_02_07"><i>XSI Interprocess Communication</i></a> .</dd><dt>GETPID</dt><dd>Return the value of <i>sempid</i>. Requires read permission.</dd><dt>GETNCNT</dt><dd>Return the value of <i>semncnt</i>. Requires read permission.</dd><dt>GETZCNT</dt><dd>Return the value of <i>semzcnt</i>. Requires read permission.</dd></dl><p>The following values of <i>cmd</i> operate on each <i>semval</i> in the set of semaphores:</p><dl compact><dt>GETALL</dt><dd>Return the value of <i>semval</i> for each semaphore in the semaphore set and place into the array pointed to by<i>arg.array</i>, where <i>arg</i> is the fourth argument to <i>semctl</i>(). Requires read permission.</dd><dt>SETALL</dt><dd>Set the value of <i>semval</i> for each semaphore in the semaphore set according to the array pointed to by <i>arg.array</i>,where <i>arg</i> is the fourth argument to <i>semctl</i>(). When this command is successfully executed, the <i>semadj</i> valuescorresponding to each specified semaphore in all processes are cleared. Requires alter permission.</dd></dl><p>The following values of <i>cmd</i> are also available:</p><dl compact><dt>IPC_STAT</dt><dd>Place the current value of each member of the <b>semid_ds</b> data structure associated with <i>semid</i> into the structurepointed to by <i>arg.buf</i>, where <i>arg</i> is the fourth argument to <i>semctl</i>(). The contents of this structure aredefined in <a href="../basedefs/sys/sem.h.html"><i><sys/sem.h></i></a>. Requires read permission.</dd><dt>IPC_SET</dt><dd>Set the value of the following members of the <b>semid_ds</b> data structure associated with <i>semid</i> to the correspondingvalue found in the structure pointed to by <i>arg.buf</i>, where <i>arg</i> is the fourth argument to <i>semctl</i>(): <pre><tt>sem_perm.uidsem_perm.gidsem_perm.mode</tt></pre><p>The mode bits specified in <a href="xsh_chap02_07.html#tag_02_07_01"><i>IPC General Description</i></a> are copied into thecorresponding bits of the <i>sem_perm.mode</i> associated with <i>semid</i>. The stored values of any other bits areunspecified.</p><p>This command can only be executed by a process that has an effective user ID equal to either that of a process with appropriateprivileges or to the value of <i>sem_perm.cuid</i> or <i>sem_perm.uid</i> in the <b>semid_ds</b> data structure associated with<i>semid</i>.</p></dd><dt>IPC_RMID</dt><dd>Remove the semaphore identifier specified by <i>semid</i> from the system and destroy the set of semaphores and <b>semid_ds</b>data structure associated with it. This command can only be executed by a process that has an effective user ID equal to eitherthat of a process with appropriate privileges or to the value of <i>sem_perm.cuid</i> or <i>sem_perm.uid</i> in the <b>semid_ds</b>data structure associated with <i>semid</i>.</dd></dl></blockquote><h4><a name="tag_03_638_04"></a>RETURN VALUE</h4><blockquote><p>If successful, the value returned by <i>semctl</i>() depends on <i>cmd</i> as follows:</p><dl compact><dt>GETVAL</dt><dd>The value of <i>semval</i>.</dd><dt>GETPID</dt><dd>The value of <i>sempid</i>.</dd><dt>GETNCNT</dt><dd>The value of <i>semncnt</i>.</dd><dt>GETZCNT</dt><dd>The value of <i>semzcnt</i>.</dd><dt>All others</dt><dd>0.</dd></dl><p>Otherwise, <i>semctl</i>() shall return -1 and set <i>errno</i> to indicate the error.</p></blockquote><h4><a name="tag_03_638_05"></a>ERRORS</h4><blockquote><p>The <i>semctl</i>() function shall fail if:</p><dl compact><dt>[EACCES]</dt><dd>Operation permission is denied to the calling process; see <a href="xsh_chap02_07.html#tag_02_07"><i>XSI InterprocessCommunication</i></a> .</dd><dt>[EINVAL]</dt><dd>The value of <i>semid</i> is not a valid semaphore identifier, or the value of <i>semnum</i> is less than 0 or greater than orequal to <i>sem_nsems</i>, or the value of <i>cmd</i> is not a valid command.</dd><dt>[EPERM]</dt><dd>The argument <i>cmd</i> is equal to IPC_RMID or IPC_SET and the effective user ID of the calling process is not equal to thatof a process with appropriate privileges and it is not equal to the value of <i>sem_perm.cuid</i> or <i>sem_perm.uid</i> in thedata structure associated with <i>semid</i>.</dd><dt>[ERANGE]</dt><dd>The argument <i>cmd</i> is equal to SETVAL or SETALL and the value to which <i>semval</i> is to be set is greater than thesystem-imposed maximum.</dd></dl></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_638_06"></a>EXAMPLES</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_638_07"></a>APPLICATION USAGE</h4><blockquote><p>The fourth parameter in the SYNOPSIS section is now specified as <tt>"..."</tt> in order to avoid a clash with the ISO Cstandard when referring to the union <i>semun</i> (as defined in Issue 3) and for backwards-compatibility.</p><p>The POSIX Realtime Extension defines alternative interfaces for interprocess communication. Application developers who need touse IPC should design their applications so that modules using the IPC routines described in <a href="xsh_chap02_07.html#tag_02_07"><i>XSI Interprocess Communication</i></a> can be easily modified to use the alternativeinterfaces.</p></blockquote><h4><a name="tag_03_638_08"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_638_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_638_10"></a>SEE ALSO</h4><blockquote><p><a href="xsh_chap02_07.html#tag_02_07"><i>XSI Interprocess Communication</i></a> , <a href="xsh_chap02_08.html#tag_02_08"><i>Realtime</i></a> , <a href="semget.html"><i>semget</i>()</a> , <a href="semop.html"><i>semop</i>()</a> , <a href="sem_close.html"><i>sem_close</i>()</a> , <a href="sem_destroy.html"><i>sem_destroy</i>()</a> , <a href="sem_getvalue.html"><i>sem_getvalue</i>()</a> , <a href="sem_init.html"><i>sem_init</i>()</a> , <a href="sem_open.html"><i>sem_open</i>()</a> , <a href="sem_post.html"><i>sem_post</i>()</a> , <a href="sem_unlink.html"><i>sem_unlink</i>()</a> , <a href="sem_wait.html"><i>sem_wait</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/sys/sem.h.html"><i><sys/sem.h></i></a></p></blockquote><h4><a name="tag_03_638_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 2. Derived from Issue 2 of the SVID.</p></blockquote><h4><a name="tag_03_638_12"></a>Issue 5</h4><blockquote><p>The note about use of POSIX Realtime Extension IPC routines has been moved from FUTURE DIRECTIONS to the APPLICATION USAGEsection.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
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