172 lines
6.8 KiB
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172 lines
6.8 KiB
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<title>pthread_attr_getguardsize</title>
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<basefont size="3"> <a name="pthread_attr_getguardsize"></a> <a name="tag_03_489"></a><!-- pthread_attr_getguardsize -->
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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_489_01"></a>NAME</h4>
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<blockquote>pthread_attr_getguardsize, pthread_attr_setguardsize - get and set the thread guardsize attribute</blockquote>
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<h4><a name="tag_03_489_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_attr_getguardsize(const pthread_attr_t *restrict</tt> <i>attr</i><tt>,<br>
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size_t *restrict</tt> <i>guardsize</i><tt>);<br>
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int pthread_attr_setguardsize(pthread_attr_t</tt> <i>*attr</i><tt>,<br>
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size_t</tt> <i>guardsize</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]"
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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_489_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>pthread_attr_getguardsize</i>() function shall get the <i>guardsize</i> attribute in the <i>attr</i> object. This
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attribute shall be returned in the <i>guardsize</i> parameter.</p>
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<p>The <i>pthread_attr_setguardsize</i>() function shall set the <i>guardsize</i> attribute in the <i>attr</i> object. The new
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value of this attribute shall be obtained from the <i>guardsize</i> parameter. If <i>guardsize</i> is zero, a guard area shall not
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be provided for threads created with <i>attr</i>. If <i>guardsize</i> is greater than zero, a guard area of at least size
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<i>guardsize</i> bytes shall be provided for each thread created with <i>attr</i>.</p>
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<p>The <i>guardsize</i> attribute controls the size of the guard area for the created thread's stack. The <i>guardsize</i>
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attribute provides protection against overflow of the stack pointer. If a thread's stack is created with guard protection, the
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implementation allocates extra memory at the overflow end of the stack as a buffer against stack overflow of the stack pointer. If
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an application overflows into this buffer an error shall result (possibly in a SIGSEGV signal being delivered to the thread).</p>
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<p>A conforming implementation may round up the value contained in <i>guardsize</i> to a multiple of the configurable system
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variable {PAGESIZE} (see <a href="../basedefs/sys/mman.h.html"><i><sys/mman.h></i></a>). If an implementation rounds up the
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value of <i>guardsize</i> to a multiple of {PAGESIZE}, a call to <i>pthread_attr_getguardsize</i>() specifying <i>attr</i> shall
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store in the <i>guardsize</i> parameter the guard size specified by the previous <i>pthread_attr_setguardsize</i>() function
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call.</p>
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<p>The default value of the <i>guardsize</i> attribute is {PAGESIZE} bytes. The actual value of {PAGESIZE} is
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implementation-defined.</p>
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<p>If the <i>stackaddr</i> or <i>stack</i> attribute has been set (that is, the caller is allocating and managing its own thread
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stacks), the <i>guardsize</i> attribute shall be ignored and no protection shall be provided by the implementation. It is the
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responsibility of the application to manage stack overflow along with stack allocation and management in this case.</p>
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</blockquote>
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<h4><a name="tag_03_489_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>If successful, the <i>pthread_attr_getguardsize</i>() and <i>pthread_attr_setguardsize</i>() functions shall return zero;
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otherwise, an error number shall be returned to indicate the error.</p>
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</blockquote>
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<h4><a name="tag_03_489_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>pthread_attr_getguardsize</i>() and <i>pthread_attr_setguardsize</i>() functions shall fail if:</p>
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<dl compact>
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<dt>[EINVAL]</dt>
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<dd>The attribute <i>attr</i> is invalid.</dd>
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<dt>[EINVAL]</dt>
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<dd>The parameter <i>guardsize</i> is invalid.</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_489_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_489_07"></a>APPLICATION USAGE</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_489_08"></a>RATIONALE</h4>
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<blockquote>
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<p>The <i>guardsize</i> attribute is provided to the application for two reasons:</p>
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<ol>
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<li>
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<p>Overflow protection can potentially result in wasted system resources. An application that creates a large number of threads,
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and which knows its threads never overflow their stack, can save system resources by turning off guard areas.</p>
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</li>
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<li>
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<p>When threads allocate large data structures on the stack, large guard areas may be needed to detect stack overflow.</p>
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</li>
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</ol>
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</blockquote>
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<h4><a name="tag_03_489_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_489_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>, <a href="../basedefs/sys/mman.h.html"><i><sys/mman.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_489_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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<h4><a name="tag_03_489_12"></a>Issue 6</h4>
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<blockquote>
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<p>In the ERRORS section, a third [EINVAL] error condition is removed as it is covered by the second error condition.</p>
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<p>The <b>restrict</b> keyword is added to the <i>pthread_attr_getguardsize</i>() prototype for alignment with the
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ISO/IEC 9899:1999 standard.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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