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>Missuses</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="../boost_dll.html" title="Chapter 14. Boost.DLL"> 10<link rel="prev" href="mangled_import.html" title="Mangled Import"> 11<link rel="next" href="reference.html" title="Reference"> 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="mangled_import.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../boost_dll.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="reference.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_dll.missuses"></a><a class="link" href="missuses.html" title="Missuses">Missuses</a> 29</h2></div></div></div> 30<div class="warning"><table border="0" summary="Warning"> 31<tr> 32<td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../doc/src/images/warning.png"></td> 33<th align="left">Warning</th> 34</tr> 35<tr><td align="left" valign="top"><p> 36 Typical errors and missuses are located in this section. Please read carefully, 37 this will save a lot of debugging time! 38 </p></td></tr> 39</table></div> 40<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 41<li class="listitem"> 42 <span class="bold"><strong>Issue:</strong></span> Program crashes on <code class="computeroutput"><span class="keyword">delete</span></code> or <code class="computeroutput"><span class="identifier">free</span><span class="special">()</span></code>. 43 </li> 44<li class="listitem"> 45 <span class="bold"><strong>Fix:</strong></span> Your plugin and program must use 46 the same Standard C++ and C libraries, both must be linked dynamically. 47 For Visual Studio use <a href="https://msdn.microsoft.com/library/2kzt1wy3%28v=vs.110%29.aspx" target="_top">/MD 48 or /MDd compiler switches</a>. 49 </li> 50</ul></div> 51<pre class="programlisting"></pre> 52<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 53<li class="listitem"> 54 <span class="bold"><strong>Issue:</strong></span> Program crashes in <code class="computeroutput"><span class="keyword">catch</span><span class="special">(...)</span></code> 55 block. 56 </li> 57<li class="listitem"> 58 <span class="bold"><strong>Example:</strong></span> 59<pre class="programlisting"><span class="keyword">try</span> <span class="special">{</span> 60 <span class="keyword">auto</span> <span class="identifier">f</span> <span class="special">=</span> <span class="identifier">dll</span><span class="special">::</span><span class="identifier">import</span><span class="special"><</span><span class="keyword">int</span><span class="special">()>(</span><span class="identifier">path_to_pugin</span><span class="special">,</span> <span class="string">"function"</span><span class="special">);</span> 61 <span class="identifier">f</span><span class="special">();</span> 62 <span class="comment">// `f` goes out of scope</span> 63<span class="special">}</span> <span class="keyword">catch</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">exception</span><span class="special">&</span> <span class="identifier">e</span><span class="special">)</span> <span class="special">{</span> 64 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cerr</span> <span class="special"><<</span> <span class="identifier">e</span><span class="special">.</span><span class="identifier">what</span><span class="special">();</span> 65<span class="special">}</span> 66</pre> 67 </li> 68<li class="listitem"> 69 <span class="bold"><strong>Fix:</strong></span> Exception was generated inside the 70 plugin, so it refers to the exception code in plugin. When <code class="computeroutput"><span class="identifier">f</span></code> goes out of scope, the plugin gets 71 unloaded and the reference to the exception code is broken. Any attempt 72 to use the exception variable may use the dangling reference, leading to 73 a segmentation fault. Fix your code: 74<pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">f</span> <span class="special">=</span> <span class="identifier">dll</span><span class="special">::</span><span class="identifier">import</span><span class="special"><</span><span class="keyword">int</span><span class="special">()>(</span><span class="identifier">path_to_pugin</span><span class="special">,</span> <span class="string">"function"</span><span class="special">);</span> 75<span class="keyword">try</span> <span class="special">{</span> 76 <span class="identifier">f</span><span class="special">();</span> 77 <span class="comment">// `f` goes out of scope</span> 78<span class="special">}</span> <span class="keyword">catch</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">exception</span><span class="special">&</span> <span class="identifier">e</span><span class="special">)</span> <span class="special">{</span> 79 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cerr</span> <span class="special"><<</span> <span class="identifier">e</span><span class="special">.</span><span class="identifier">what</span><span class="special">();</span> 80<span class="special">}</span> 81</pre> 82 </li> 83</ul></div> 84<pre class="programlisting"></pre> 85<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 86<li class="listitem"> 87 <span class="bold"><strong>Issue:</strong></span> Thread local storage seems to be 88 corrupted. 89 </li> 90<li class="listitem"> 91 <span class="bold"><strong>Fix:</strong></span> Some platforms have no out-of-the-box 92 support for plugins that use TLS, for example <a href="https://support.microsoft.com/en-us/kb/118816" target="_top">Windows</a>. 93 Use platform specific workarounds or just do not use TLS in plugins. 94 </li> 95</ul></div> 96<pre class="programlisting"></pre> 97<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 98<li class="listitem"> 99 <span class="bold"><strong>Issue:</strong></span> Attempt to call a loaded function 100 crashes or function returns incorrect result. 101 </li> 102<li class="listitem"> 103 <span class="bold"><strong>Fix:</strong></span> Boost.DLL does not guarantee ABI 104 stability. If you compile plugin and program with different compilers or 105 different compiler switches the function ABI may change and you'll end 106 up with incorrect code. 107 </li> 108</ul></div> 109<pre class="programlisting"></pre> 110<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> 111<li class="listitem"> 112 <span class="bold"><strong>Issue:</strong></span> Program crashes after plugin unload. 113 </li> 114<li class="listitem"> 115 <span class="bold"><strong>Example:</strong></span> 116<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span> <span class="special">{</span> 117 <span class="identifier">shared_ptr</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">p</span><span class="special">;</span> 118 <span class="keyword">try</span> <span class="special">{</span> 119 <span class="keyword">auto</span> <span class="identifier">f</span> <span class="special">=</span> <span class="identifier">dll</span><span class="special">::</span><span class="identifier">import</span><span class="special"><</span><span class="identifier">shared_ptr</span><span class="special"><</span><span class="keyword">int</span><span class="special">>()>(</span><span class="identifier">path_to_pugin</span><span class="special">,</span> <span class="string">"function"</span><span class="special">);</span> 120 <span class="identifier">p</span> <span class="special">=</span> <span class="identifier">f</span><span class="special">();</span> 121 <span class="comment">// `f` goes out of scope</span> 122 <span class="special">}</span> <span class="keyword">catch</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">exception</span><span class="special">&</span> <span class="identifier">e</span><span class="special">)</span> <span class="special">{</span> 123 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cerr</span> <span class="special"><<</span> <span class="identifier">e</span><span class="special">.</span><span class="identifier">what</span><span class="special">();</span> 124 <span class="special">}</span> 125 <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="special">*</span><span class="identifier">p</span><span class="special">;</span> 126 <span class="comment">// crashes here</span> 127<span class="special">}</span> 128</pre> 129 </li> 130<li class="listitem"> 131 <span class="bold"><strong>Fix:</strong></span> In that particular example the problem 132 is within <code class="computeroutput"><span class="identifier">shared_ptr</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span></code>. 133 It keeps a type erased deleter, code for that deleter is located in plugin. 134 On destruction of <code class="computeroutput"><span class="identifier">p</span></code>, <code class="computeroutput"><span class="identifier">shared_ptr</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span></code> 135 attempts to call that deleter, however the plugin was already unloaded 136 and the code for deleter is not available any more. 137 </li> 138<li class="listitem"> 139 <span class="bold"><strong>Rule of thumb:</strong></span>: if your plugin method 140 returns any C++ class variable, then make sure that the plugin is loaded 141 until that variable and any of its copies are in scope. 142 </li> 143<li class="listitem"> 144 <span class="bold"><strong>Typical classes that cause such errors are:</strong></span> 145 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "> 146<li class="listitem"> 147 <code class="computeroutput"><span class="identifier">any</span></code> 148 </li> 149<li class="listitem"> 150 <code class="computeroutput"><span class="identifier">function</span></code> 151 </li> 152<li class="listitem"> 153 <code class="computeroutput"><span class="identifier">shared_ptr</span></code> 154 </li> 155<li class="listitem"> 156 any container with polymorphic allocator 157 </li> 158<li class="listitem"> 159 <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">type_index</span></code> 160 </li> 161<li class="listitem"> 162 <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">type_info</span></code> 163 </li> 164<li class="listitem"> 165 <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">exception_ptr</span></code> 166 </li> 167<li class="listitem"> 168 <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">Base</span><span class="special">></span></code> 169 holding a <code class="computeroutput"><span class="identifier">Derived</span></code> 170 type from plugin 171 </li> 172<li class="listitem"> 173 exception classes thrown from plugin 174 </li> 175</ul></div> 176 </li> 177</ul></div> 178<pre class="programlisting"></pre> 179</div> 180<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 181<td align="left"></td> 182<td align="right"><div class="copyright-footer">Copyright © 2014 Renato Tegon Forti, Antony Polukhin<br>Copyright © 2015 Antony Polukhin<br>Copyright © 2016 Antony Polukhin, Klemens Morgenstern<br>Copyright © 2017-2019 Antony Polukhin<p> 183 Distributed under the Boost Software License, Version 1.0. (See accompanying 184 file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 185 </p> 186</div></td> 187</tr></table> 188<hr> 189<div class="spirit-nav"> 190<a accesskey="p" href="mangled_import.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../boost_dll.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="reference.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 191</div> 192</body> 193</html> 194
