154 lines
5.9 KiB
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154 lines
5.9 KiB
HTML
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<title>pthread_getconcurrency</title>
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<basefont size="3"> <a name="pthread_getconcurrency"></a> <a name="tag_03_529"></a><!-- pthread_getconcurrency -->
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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_529_01"></a>NAME</h4>
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<blockquote>pthread_getconcurrency, pthread_setconcurrency - get and set the level of concurrency</blockquote>
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<h4><a name="tag_03_529_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/pthread.h.html">pthread.h</a>><br>
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<br>
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int pthread_getconcurrency(void);<br>
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int pthread_setconcurrency(int</tt> <i>new_level</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]" border=
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"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_529_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>Unbound threads in a process may or may not be required to be simultaneously active. By default, the threads implementation
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ensures that a sufficient number of threads are active so that the process can continue to make progress. While this conserves
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system resources, it may not produce the most effective level of concurrency.</p>
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<p>The <i>pthread_setconcurrency</i>() function allows an application to inform the threads implementation of its desired
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concurrency level, <i>new_level</i>. The actual level of concurrency provided by the implementation as a result of this function
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call is unspecified.</p>
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<p>If <i>new_level</i> is zero, it causes the implementation to maintain the concurrency level at its discretion as if
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<i>pthread_setconcurrency</i>() had never been called.</p>
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<p>The <i>pthread_getconcurrency</i>() function shall return the value set by a previous call to the
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<i>pthread_setconcurrency</i>() function. If the <i>pthread_setconcurrency</i>() function was not previously called, this function
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shall return zero to indicate that the implementation is maintaining the concurrency level.</p>
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<p>A call to <i>pthread_setconcurrency</i>() shall inform the implementation of its desired concurrency level. The implementation
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shall use this as a hint, not a requirement.</p>
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<p>If an implementation does not support multiplexing of user threads on top of several kernel-scheduled entities, the
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<i>pthread_setconcurrency</i>() and <i>pthread_getconcurrency</i>() functions are provided for source code compatibility but they
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shall have no effect when called. To maintain the function semantics, the <i>new_level</i> parameter is saved when
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<i>pthread_setconcurrency</i>() is called so that a subsequent call to <i>pthread_getconcurrency</i>() shall return the same
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value.</p>
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</blockquote>
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<h4><a name="tag_03_529_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>If successful, the <i>pthread_setconcurrency</i>() function shall return zero; otherwise, an error number shall be returned to
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indicate the error.</p>
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<p>The <i>pthread_getconcurrency</i>() function shall always return the concurrency level set by a previous call to
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<i>pthread_setconcurrency</i>(). If the <i>pthread_setconcurrency</i>() function has never been called,
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<i>pthread_getconcurrency</i>() shall return zero.</p>
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</blockquote>
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<h4><a name="tag_03_529_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>pthread_setconcurrency</i>() function shall fail if:</p>
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<dl compact>
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<dt>[EINVAL]</dt>
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<dd>The value specified by <i>new_level</i> is negative.</dd>
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<dt>[EAGAIN]</dt>
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<dd>The value specific by <i>new_level</i> would cause a system resource to be exceeded.</dd>
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</dl>
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<p>These functions shall not return an error code of [EINTR].</p>
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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_529_06"></a>EXAMPLES</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_529_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>Use of these functions changes the state of the underlying concurrency upon which the application depends. Library developers
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are advised to not use the <i>pthread_getconcurrency</i>() and <i>pthread_setconcurrency</i>() functions since their use may
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conflict with an applications use of these functions.</p>
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</blockquote>
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<h4><a name="tag_03_529_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_529_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_529_10"></a>SEE ALSO</h4>
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<blockquote>
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<p>The Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/pthread.h.html"><i><pthread.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_529_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 5.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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