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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>pthread_attr_getguardsize</title></head><body bgcolor=white><center><font size=2>The Single UNIX ® Specification, Version 2<br>Copyright © 1997 The Open Group</font></center><hr size=2 noshade><h4><a name = "tag_000_007_1135"> </a>NAME</h4><blockquote>pthread_attr_getguardsize, pthread_attr_setguardsize -get or set the thread guardsize attribute</blockquote><h4><a name = "tag_000_007_1136"> </a>SYNOPSIS</h4><blockquote><pre><code>#include <<a href="pthread.h.html">pthread.h</a>>int pthread_attr_getguardsize(const pthread_attr_t <i>*attr</i>, size_t <i>*guardsize</i>);int pthread_attr_setguardsize(pthread_attr_t <i>*attr</i>, size_t <i>guardsize</i>);</code></pre></blockquote><h4><a name = "tag_000_007_1137"> </a>DESCRIPTION</h4><blockquote>The <i>guardsize</i> attribute controls the sizeof the guard area for the created thread's stack. The <i>guardsize</i>attribute provides protection against overflow of thestack pointer. If a thread's stack is created with guardprotection, the implementation allocates extramemory at the overflow end of the stack as a buffer againststack overflow of the stack pointer. If an applicationoverflows into this buffer an error results (possiblyin a SIGSEGV signal being delivered to the thread).<p>The <i>guardsize</i> attribute is provided to the applicationfor two reasons:<ol type = 1><p><li>Overflow protection can potentiallyresult in wasted system resources. An application that creates a largenumber of threads, and which knows its threads will never overflowtheir stack, can save system resources by turning off guard areas.<p><li>When threads allocate large data structures on the stack,large guard areas may be needed to detect stack overflow.<p></ol><p>The <i>pthread_attr_getguardsize()</i>function gets the<i>guardsize</i> attribute in the <i>attr</i> object. This attribute isreturned in the <i>guardsize</i> parameter.<p>The <i>pthread_attr_setguardsize()</i>function sets the<i>guardsize</i> attribute in the <i>attr</i> object. The new value ofthis attribute is obtained from the <i>guardsize</i> parameter.If <i>guardsize</i> is zero, a guard area will not beprovided for threads created with <i>attr</i>. If <i>guardsize</i> isgreaterthan zero, a guard area of at least size <i>guardsize</i>bytes is provided for each thread created with <i>attr</i>.<p>A conforming implementation is permitted to round upthe value contained in <i>guardsize</i> to a multipleof the configurable system variable PAGESIZE (see <i><a href="sysmman.h.html"><sys/mman.h></a></i>).If an implementation rounds up thevalue of <i>guardsize</i> to a multiple of PAGESIZE, a call to<i>pthread_attr_getguardsize()</i>specifying <i>attr</i> willstore in the <i>guardsize</i> parameter the guard size specified by theprevious <i>pthread_attr_setguardsize()</i>function call.<p>The default value of the <i>guardsize</i> attribute is PAGESIZE bytes.The actual value of PAGESIZE isimplementation-dependent and may not be the same on all implementations.<p>If the <i>stackaddr</i> attribute has been set (that is, the calleris allocating and managing its own thread stacks), the<i>guardsize</i> attribute is ignored and no protectionwill be provided by the implementation. It is theresponsibility of the application to manage stack overflowalong with stack allocation and management in thiscase.</blockquote><h4><a name = "tag_000_007_1138"> </a>RETURN VALUE</h4><blockquote>If successful, the <i>pthread_attr_getguardsize()</i>and<i>pthread_attr_setguardsize()</i>functions return zero.Otherwise, an error number is returned to indicate the error.<br></blockquote><h4><a name = "tag_000_007_1139"> </a>ERRORS</h4><blockquote>The<i>pthread_attr_getguardsize()</i>and<i>pthread_attr_setguardsize()</i>functions will fail if:<dl compact><dt>[EINVAL]<dd>The attribute <i>attr</i> is invalid.<dt>[EINVAL]<dd>The parameter <i>guardsize</i> is invalid.<dt>[EINVAL]<dd>The parameter <i>guardsize</i> contains an invalid value.</dl></blockquote><h4><a name = "tag_000_007_1140"> </a>EXAMPLES</h4><blockquote>None.</blockquote><h4><a name = "tag_000_007_1141"> </a>APPLICATION USAGE</h4><blockquote>None.</blockquote><h4><a name = "tag_000_007_1142"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_000_007_1143"> </a>SEE ALSO</h4><blockquote><i><a href="pthread.h.html"><pthread.h></a></i>.</blockquote><hr size=2 noshade><center><font size=2>UNIX ® is a registered Trademark of The Open Group.<br>Copyright © 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>⌨️ 快捷键说明
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