218 lines
8.3 KiB
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218 lines
8.3 KiB
HTML
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<title>getpriority</title>
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<basefont size="3"> <a name="getpriority"></a> <a name="tag_03_241"></a><!-- getpriority -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_241_01"></a>NAME</h4>
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<blockquote>getpriority, setpriority - get and set the nice value</blockquote>
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<h4><a name="tag_03_241_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> #include <<a href="../basedefs/sys/resource.h.html">sys/resource.h</a>><br>
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<br>
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int getpriority(int</tt> <i>which</i><tt>, id_t</tt> <i>who</i><tt>);<br>
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int setpriority(int</tt> <i>which</i><tt>, id_t</tt> <i>who</i><tt>, int</tt> <i>value</i><tt>); <img src="../images/opt-end.gif"
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alt="[Option End]" border="0"></tt></code></div>
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<tt><br>
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</tt></blockquote>
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<h4><a name="tag_03_241_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>getpriority</i>() function shall obtain the nice value of a process, process group, or user. The <i>setpriority</i>()
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function shall set the nice value of a process, process group, or user to <i>value</i>+ {NZERO}.</p>
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<p>Target processes are specified by the values of the <i>which</i> and <i>who</i> arguments. The <i>which</i> argument may be one
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of the following values: PRIO_PROCESS, PRIO_PGRP, or PRIO_USER, indicating that the <i>who</i> argument is to be interpreted as a
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process ID, a process group ID, or an effective user ID, respectively. A 0 value for the <i>who</i> argument specifies the current
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process, process group, or user.</p>
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<p>The nice value set with <i>setpriority</i>() shall be applied to the process. If the process is multi-threaded, the nice value
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shall affect all system scope threads in the process.</p>
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<p>If more than one process is specified, <i>getpriority</i>() shall return value {NZERO} less than the lowest nice value
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pertaining to any of the specified processes, and <i>setpriority</i>() shall set the nice values of all of the specified processes
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to <i>value</i>+ {NZERO}.</p>
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<p>The default nice value is {NZERO}; lower nice values shall cause more favorable scheduling. While the range of valid nice values
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is [0,{NZERO}*2-1], implementations may enforce more restrictive limits. If <i>value</i>+ {NZERO} is less than the system's lowest
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supported nice value, <i>setpriority</i>() shall set the nice value to the lowest supported value; if <i>value</i>+ {NZERO} is
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greater than the system's highest supported nice value, <i>setpriority</i>() shall set the nice value to the highest supported
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value.</p>
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<p>Only a process with appropriate privileges can lower its nice value.</p>
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<p><sup>[<a href="javascript:open_code('PS')">PS|TPS</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0">
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Any processes or threads using SCHED_FIFO or SCHED_RR shall be unaffected by a call to <i>setpriority</i>(). This is not considered
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an error. A process which subsequently reverts to SCHED_OTHER need not have its priority affected by such a <i>setpriority</i>()
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call. <img src="../images/opt-end.gif" alt="[Option End]" border="0"></p>
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<p>The effect of changing the nice value may vary depending on the process-scheduling algorithm in effect.</p>
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<p>Since <i>getpriority</i>() can return the value -1 on successful completion, it is necessary to set <i>errno</i> to 0 prior to a
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call to <i>getpriority</i>(). If <i>getpriority</i>() returns the value -1, then <i>errno</i> can be checked to see if an error
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occurred or if the value is a legitimate nice value.</p>
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</blockquote>
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<h4><a name="tag_03_241_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, <i>getpriority</i>() shall return an integer in the range -{NZERO} to {NZERO}-1. Otherwise, -1 shall
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be returned and <i>errno</i> set to indicate the error.</p>
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<p>Upon successful completion, <i>setpriority</i>() shall return 0; otherwise, -1 shall be returned and <i>errno</i> set to
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indicate the error.</p>
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</blockquote>
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<h4><a name="tag_03_241_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>getpriority</i>() and <i>setpriority</i>() functions shall fail if:</p>
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<dl compact>
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<dt>[ESRCH]</dt>
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<dd>No process could be located using the <i>which</i> and <i>who</i> argument values specified.</dd>
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<dt>[EINVAL]</dt>
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<dd>The value of the <i>which</i> argument was not recognized, or the value of the <i>who</i> argument is not a valid process ID,
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process group ID, or user ID.</dd>
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</dl>
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<p>In addition, <i>setpriority</i>() may fail if:</p>
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<dl compact>
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<dt>[EPERM]</dt>
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<dd>A process was located, but neither the real nor effective user ID of the executing process match the effective user ID of the
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process whose nice value is being changed.</dd>
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<dt>[EACCES]</dt>
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<dd>A request was made to change the nice value to a lower numeric value and the current process does not have appropriate
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privileges.</dd>
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</dl>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_241_06"></a>EXAMPLES</h4>
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<blockquote>
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<h5><a name="tag_03_241_06_01"></a>Using getpriority()</h5>
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<p>The following example returns the current scheduling priority for the process ID returned by the call to <a href=
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"../functions/getpid.html"><i>getpid</i>()</a>.</p>
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<pre>
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<tt>#include <sys/resource.h>
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...
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int which = PRIO_PROCESS;
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id_t pid;
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int ret;
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<br>
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pid = getpid();
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ret = getpriority(which, pid);
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</tt>
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</pre>
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<h5><a name="tag_03_241_06_02"></a>Using setpriority()</h5>
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<p>The following example sets the priority for the current process ID to -20.</p>
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<pre>
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<tt>#include <sys/resource.h>
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...
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int which = PRIO_PROCESS;
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id_t pid;
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int priority = -20;
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int ret;
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<br>
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pid = getpid();
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ret = setpriority(which, pid, priority);
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</tt>
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</pre>
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</blockquote>
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<h4><a name="tag_03_241_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>The <i>getpriority</i>() and <i>setpriority</i>() functions work with an offset nice value (nice value -{NZERO}). The nice value
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is in the range [0,2*{NZERO} -1], while the return value for <i>getpriority</i>() and the third parameter for <i>setpriority</i>()
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are in the range [-{NZERO},{NZERO} -1].</p>
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</blockquote>
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<h4><a name="tag_03_241_08"></a>RATIONALE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_241_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_241_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="nice.html"><i>nice</i>()</a> , <a href="sched_get_priority_max.html"><i>sched_get_priority_max</i>()</a> , <a href=
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"sched_setscheduler.html"><i>sched_setscheduler</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/sys/resource.h.html"><i><sys/resource.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_241_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 4, Version 2.</p>
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</blockquote>
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<h4><a name="tag_03_241_12"></a>Issue 5</h4>
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<blockquote>
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<p>Moved from X/OPEN UNIX extension to BASE.</p>
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<p>The DESCRIPTION is reworded in terms of the nice value rather than <i>priority</i> to avoid confusion with functionality in the
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POSIX Realtime Extension.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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<hr>
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<center><font size="2"><!--footer start-->
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href=
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"../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>
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