169 lines
7.1 KiB
HTML
169 lines
7.1 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<meta name="generator" content="HTML Tidy, see www.w3.org">
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<link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 -->
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>vfork</title>
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</head>
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<body bgcolor="white">
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<script type="text/javascript" language="JavaScript" src="../jscript/codes.js">
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</script>
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<basefont size="3"> <a name="vfork"></a> <a name="tag_03_809"></a><!-- vfork -->
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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_809_01"></a>NAME</h4>
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<blockquote>vfork - create a new process; share virtual memory</blockquote>
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<h4><a name="tag_03_809_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('OB XSI')">OB XSI</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> #include <<a href="../basedefs/unistd.h.html">unistd.h</a>><br>
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<br>
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pid_t vfork(void); <img src="../images/opt-end.gif" 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_809_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>vfork</i>() function shall be equivalent to <a href="../functions/fork.html"><i>fork</i>()</a>, except that the behavior
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is undefined if the process created by <i>vfork</i>() either modifies any data other than a variable of type <b>pid_t</b> used to
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store the return value from <i>vfork</i>(), or returns from the function in which <i>vfork</i>() was called, or calls any other
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function before successfully calling <a href="../functions/_exit.html"><i>_exit</i>()</a> or one of the <i><a href=
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"../functions/exec.html">exec</a></i> family of functions.</p>
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</blockquote>
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<h4><a name="tag_03_809_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, <i>vfork</i>() shall return 0 to the child process and return the process ID of the child process to
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the parent process. Otherwise, -1 shall be returned to the parent, no child process shall be created, and <i>errno</i> shall be set
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to indicate the error.</p>
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</blockquote>
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<h4><a name="tag_03_809_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>vfork</i>() function shall fail if:</p>
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<dl compact>
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<dt>[EAGAIN]</dt>
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<dd>The system-wide limit on the total number of processes under execution would be exceeded, or the system-imposed limit on the
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total number of processes under execution by a single user would be exceeded.</dd>
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<dt>[ENOMEM]</dt>
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<dd>There is insufficient swap space for the new process.</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_809_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_809_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>Conforming applications are recommended not to depend on <i>vfork</i>(), but to use <a href=
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"../functions/fork.html"><i>fork</i>()</a> instead. The <i>vfork</i>() function may be withdrawn in a future version.</p>
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<p>On some implementations, <i>vfork</i>() is equivalent to <a href="../functions/fork.html"><i>fork</i>()</a>.</p>
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<p>The <i>vfork</i>() function differs from <a href="../functions/fork.html"><i>fork</i>()</a> only in that the child process can
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share code and data with the calling process (parent process). This speeds cloning activity significantly at a risk to the
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integrity of the parent process if <i>vfork</i>() is misused.</p>
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<p>The use of <i>vfork</i>() for any purpose except as a prelude to an immediate call to a function from the <i><a href=
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"../functions/exec.html">exec</a></i> family, or to <a href="../functions/_exit.html"><i>_exit</i>()</a>, is not advised.</p>
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<p>The <i>vfork</i>() function can be used to create new processes without fully copying the address space of the old process. If a
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forked process is simply going to call <i><a href="../functions/exec.html">exec</a></i>, the data space copied from the parent to
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the child by <a href="../functions/fork.html"><i>fork</i>()</a> is not used. This is particularly inefficient in a paged
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environment, making <i>vfork</i>() particularly useful. Depending upon the size of the parent's data space, <i>vfork</i>() can give
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a significant performance improvement over <a href="../functions/fork.html"><i>fork</i>()</a>.</p>
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<p>The <i>vfork</i>() function can normally be used just like <a href="../functions/fork.html"><i>fork</i>()</a>. It does not work,
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however, to return while running in the child's context from the caller of <i>vfork</i>() since the eventual return from
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<i>vfork</i>() would then return to a no longer existent stack frame. Care should be taken, also, to call <a href=
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"../functions/_exit.html"><i>_exit</i>()</a> rather than <a href="../functions/exit.html"><i>exit</i>()</a> if <i><a href=
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"../functions/exec.html">exec</a></i> cannot be used, since <a href="../functions/exit.html"><i>exit</i>()</a> flushes and closes
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standard I/O channels, thereby damaging the parent process' standard I/O data structures. (Even with <a href=
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"../functions/fork.html"><i>fork</i>()</a>, it is wrong to call <a href="../functions/exit.html"><i>exit</i>()</a>, since buffered
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data would then be flushed twice.)</p>
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<p>If signal handlers are invoked in the child process after <i>vfork</i>(), they must follow the same rules as other code in the
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child process.</p>
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</blockquote>
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<h4><a name="tag_03_809_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_809_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>This function may be withdrawn in a future version.</p>
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</blockquote>
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<h4><a name="tag_03_809_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="exec.html"><i><a href="../functions/exec.html">exec</a></i>()</a> , <a href="exit.html"><i>exit</i>()</a> , <a href=
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"fork.html"><i>fork</i>()</a> , <a href="wait.html"><i>wait</i>()</a> , the Base Definitions volume of
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IEEE Std 1003.1-2001, <a href="../basedefs/unistd.h.html"><i><unistd.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_809_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_809_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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</blockquote>
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<h4><a name="tag_03_809_13"></a>Issue 6</h4>
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<blockquote>
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<p>This function is marked obsolescent.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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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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