1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<head> 4<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 5<title>Concepts</title> 6<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> 7<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 8<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> 9<link rel="up" href="../process.html" title="Chapter 29. Boost.Process"> 10<link rel="prev" href="../process.html" title="Chapter 29. Boost.Process"> 11<link rel="next" href="tutorial.html" title="Tutorial"> 12</head> 13<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 14<table cellpadding="2" width="100%"><tr> 15<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> 16<td align="center"><a href="../../../index.html">Home</a></td> 17<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> 18<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 19<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 20<td align="center"><a href="../../../more/index.htm">More</a></td> 21</tr></table> 22<hr> 23<div class="spirit-nav"> 24<a accesskey="p" href="../process.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../process.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="tutorial.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 25</div> 26<div class="section"> 27<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 28<a name="boost_process.concepts"></a><a class="link" href="concepts.html" title="Concepts">Concepts</a> 29</h2></div></div></div> 30<div class="toc"><dl class="toc"> 31<dt><span class="section"><a href="concepts.html#boost_process.concepts.pipes">Pipes</a></span></dt> 32<dt><span class="section"><a href="concepts.html#boost_process.concepts.process">Processes</a></span></dt> 33<dt><span class="section"><a href="concepts.html#boost_process.concepts.env">Environment</a></span></dt> 34</dl></div> 35<p> 36 In this section, some of the underlying concepts of the operating system used 37 in this library, will be explained. In the following chapters we will presume 38 knowledge of that. Though please note, that this is a short summary and not 39 conclusive of everything that can be done. 40 </p> 41<p> 42 The goal of this library is to implement a portable wrapper, so that we will 43 explain mostly what windows and posix have in common. 44 </p> 45<div class="section"> 46<div class="titlepage"><div><div><h3 class="title"> 47<a name="boost_process.concepts.pipes"></a><a class="link" href="concepts.html#boost_process.concepts.pipes" title="Pipes">Pipes</a> 48</h3></div></div></div> 49<div class="toc"><dl class="toc"> 50<dt><span class="section"><a href="concepts.html#boost_process.concepts.pipes.anonymous">Anonymous Pipes</a></span></dt> 51<dt><span class="section"><a href="concepts.html#boost_process.concepts.pipes.named">Named Pipes</a></span></dt> 52</dl></div> 53<p> 54 Pipes are a facility for communication between different threads, processes 55 and in some cases machines, the operating system provides. 56 </p> 57<p> 58 The typical feature of a pipe is, that it is one channel, to which two handles 59 are given, one for reading (source), one for writing (sink). In that it is 60 different than other facilities (like sockets) and provides another way to 61 manage the connectivity: if one side of the pipe is closed (i.e. the pipe 62 is broken), the other is notified. 63 </p> 64<p> 65 Pipes are typically used for interprocess communication. The main reason 66 is, that pipes can be directly assigned to the process stdio, i.e. stderr, 67 stdin and stdout. Additionally, half of the pipe can be inherited to the 68 child process and closed in the father process. This will cause the pipe 69 to be broken when the child process exits. 70 </p> 71<p> 72 Though please note, that if the same thread reads and writes to a pipe, it 73 will only talk to itself. 74 </p> 75<div class="section"> 76<div class="titlepage"><div><div><h4 class="title"> 77<a name="boost_process.concepts.pipes.anonymous"></a><a class="link" href="concepts.html#boost_process.concepts.pipes.anonymous" title="Anonymous Pipes">Anonymous Pipes</a> 78</h4></div></div></div> 79<p> 80 The most common pipes are anonymous. Since they have no name, a handle 81 to them can only be obtained from duplicating either handle. 82 </p> 83<p> 84 In this library the following functions are used for the creation of unnamed 85 pipes: 86 </p> 87<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 88<li class="listitem"> 89 <a href="http://pubs.opengroup.org/onlinepubs/7908799/xsh/pipe.html" target="_top">posix</a> 90 </li> 91<li class="listitem"> 92 <a href="https://msdn.microsoft.com/de-de/library/windows/desktop/aa365152.aspx" target="_top">windows</a> 93 </li> 94</ul></div> 95</div> 96<div class="section"> 97<div class="titlepage"><div><div><h4 class="title"> 98<a name="boost_process.concepts.pipes.named"></a><a class="link" href="concepts.html#boost_process.concepts.pipes.named" title="Named Pipes">Named Pipes</a> 99</h4></div></div></div> 100<p> 101 As the name suggests, named pipes have a string identifier. This means 102 that a handle to them can be obtained with the identifier, too. 103 </p> 104<p> 105 The implementation on posix uses <a href="(http://pubs.opengroup.org/onlinepubs/009695399/functions/mkfifo.html" target="_top">fifos</a>, 106 which means, that the named pipe behaves like a file. 107 </p> 108<p> 109 Windows does provide a facility called <a href="https://msdn.microsoft.com/en-us/library/windows/desktop/aa365150(v=vs.85).aspx" target="_top">named 110 pipes</a>, which also have file-like names, but are in a different 111 scope than the actual file system. 112 </p> 113<div class="note"><table border="0" summary="Note"> 114<tr> 115<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td> 116<th align="left">Note</th> 117</tr> 118<tr><td align="left" valign="top"><p> 119 The main reason named pipes are part of this library, is because they 120 need to be internally used for asynchrounous communication on windows. 121 </p></td></tr> 122</table></div> 123</div> 124</div> 125<div class="section"> 126<div class="titlepage"><div><div><h3 class="title"> 127<a name="boost_process.concepts.process"></a><a class="link" href="concepts.html#boost_process.concepts.process" title="Processes">Processes</a> 128</h3></div></div></div> 129<div class="toc"><dl class="toc"> 130<dt><span class="section"><a href="concepts.html#boost_process.concepts.process.exit_code">Exit code</a></span></dt> 131<dt><span class="section"><a href="concepts.html#boost_process.concepts.process.termination">Termination</a></span></dt> 132</dl></div> 133<p> 134 A process is an independently executable entity, which is different from 135 a thread, in that it has its own resources. Those include memory and hardware 136 resources. 137 </p> 138<p> 139 Every process is identified by a unique number<a href="#ftn.boost_process.concepts.process.f0" class="footnote" name="boost_process.concepts.process.f0"><sup class="footnote">[28]</sup></a>, called the process identification digit, <code class="computeroutput"><span class="identifier">pid</span></code>. 140 </p> 141<div class="section"> 142<div class="titlepage"><div><div><h4 class="title"> 143<a name="boost_process.concepts.process.exit_code"></a><a class="link" href="concepts.html#boost_process.concepts.process.exit_code" title="Exit code">Exit code</a> 144</h4></div></div></div> 145<p> 146 A process will return an integer value indicating whether it was successful. 147 On posix there are more codes associated with that, but not so on windows. 148 Therefore there is no such encoding currently in the library. However an 149 exit code of zero means the process was successful, while one different 150 than zero indicates an error. 151 </p> 152</div> 153<div class="section"> 154<div class="titlepage"><div><div><h4 class="title"> 155<a name="boost_process.concepts.process.termination"></a><a class="link" href="concepts.html#boost_process.concepts.process.termination" title="Termination">Termination</a> 156</h4></div></div></div> 157<p> 158 Processes can also be forced to exit. There are two ways to do this, signal 159 the process to do so and wait, and just terminate the process without conditions. 160 </p> 161<p> 162 Usually the first approach is to signal an exit request, but windows - 163 unlike posix - does not provide a consistent way to do this. Hence this 164 is not part of the library and only the hard terminate is. 165 </p> 166</div> 167</div> 168<div class="section"> 169<div class="titlepage"><div><div><h3 class="title"> 170<a name="boost_process.concepts.env"></a><a class="link" href="concepts.html#boost_process.concepts.env" title="Environment">Environment</a> 171</h3></div></div></div> 172<p> 173 The environment is a map of variables local to every process. The most significant 174 one for this library is the <code class="computeroutput"><span class="identifier">PATH</span></code> 175 variable, which contains a list of paths, that ought to be searched for executables. 176 A shell will do this automatically, while this library provides a function 177 for that. 178 </p> 179</div> 180<div class="footnotes"> 181<br><hr style="width:100; text-align:left;margin-left: 0"> 182<div id="ftn.boost_process.concepts.process.f0" class="footnote"><p><a href="#boost_process.concepts.process.f0" class="para"><sup class="para">[28] </sup></a> 183 it is unique as long as the process is active 184 </p></div> 185</div> 186</div> 187<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 188<td align="left"></td> 189<td align="right"><div class="copyright-footer">Copyright © 2006-2012 Julio M. Merino Vidal, Ilya Sokolov, 190 Felipe Tanus, Jeff Flinn, Boris Schaeling<br>Copyright © 2016 Klemens D. Morgenstern<p> 191 Distributed under the Boost Software License, Version 1.0. (See accompanying 192 file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 193 </p> 194</div></td> 195</tr></table> 196<hr> 197<div class="spirit-nav"> 198<a accesskey="p" href="../process.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../process.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="tutorial.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 199</div> 200</body> 201</html> 202
