1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
|
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<title>Missuses</title>
<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css">
<meta name="generator" content="DocBook XSL Stylesheets V1.79.1">
<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset">
<link rel="up" href="../boost_dll.html" title="Chapter 12. Boost.DLL">
<link rel="prev" href="mangled_import.html" title="Mangled Import">
<link rel="next" href="reference.html" title="Reference">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<table cellpadding="2" width="100%"><tr>
<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td>
<td align="center"><a href="../../../index.html">Home</a></td>
<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td>
<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
<td align="center"><a href="../../../more/index.htm">More</a></td>
</tr></table>
<hr>
<div class="spirit-nav">
<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>
</div>
<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="boost_dll.missuses"></a><a class="link" href="missuses.html" title="Missuses">Missuses</a>
</h2></div></div></div>
<div class="warning"><table border="0" summary="Warning">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../doc/src/images/warning.png"></td>
<th align="left">Warning</th>
</tr>
<tr><td align="left" valign="top"><p>
Typical errors and missuses are located in this section. Please read carefully,
this will save a lot of debugging time!
</p></td></tr>
</table></div>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<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>.
</li>
<li class="listitem">
<span class="bold"><strong>Fix:</strong></span> Your plugin and program must use
the same Standard C++ and C libraries, both must be linked dynamically.
For Visual Studio use <a href="https://msdn.microsoft.com/library/2kzt1wy3%28v=vs.110%29.aspx" target="_top">/MD
or /MDd compiler switches</a>.
</li>
</ul></div>
<pre class="programlisting"></pre>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<span class="bold"><strong>Issue:</strong></span> Program crashes in <code class="computeroutput"><span class="keyword">catch</span><span class="special">(...)</span></code>
block.
</li>
<li class="listitem">
<span class="bold"><strong>Example:</strong></span>
<pre class="programlisting"><span class="keyword">try</span> <span class="special">{</span>
<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>
<span class="identifier">f</span><span class="special">();</span>
<span class="comment">// `f` goes out of scope</span>
<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>
<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>
<span class="special">}</span>
</pre>
</li>
<li class="listitem">
<span class="bold"><strong>Fix:</strong></span> Exception was generated inside the
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
unloaded and the reference to the exception code is broken. Any attempt
to use the exception variable may use the dangling reference, leading to
a segmentation fault. Fix your code:
<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>
<span class="keyword">try</span> <span class="special">{</span>
<span class="identifier">f</span><span class="special">();</span>
<span class="comment">// `f` goes out of scope</span>
<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>
<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>
<span class="special">}</span>
</pre>
</li>
</ul></div>
<pre class="programlisting"></pre>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<span class="bold"><strong>Issue:</strong></span> Thread local storage seems to be
corrupted.
</li>
<li class="listitem">
<span class="bold"><strong>Fix:</strong></span> Some platforms have no out-of-the-box
support for plugins that use TLS, for example <a href="https://support.microsoft.com/en-us/kb/118816" target="_top">Windows</a>.
Use platform specific workarounds or just do not use TLS in plugins.
</li>
</ul></div>
<pre class="programlisting"></pre>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<span class="bold"><strong>Issue:</strong></span> Attempt to call a loaded function
crashes or function returns incorrect result.
</li>
<li class="listitem">
<span class="bold"><strong>Fix:</strong></span> Boost.DLL does not guarantee ABI
stability. If you compile plugin and program with different compilers or
different compiler switches the function ABI may change and you'll end
up with incorrect code.
</li>
</ul></div>
<pre class="programlisting"></pre>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
<span class="bold"><strong>Issue:</strong></span> Program crashes after plugin unload.
</li>
<li class="listitem">
<span class="bold"><strong>Example:</strong></span>
<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</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">p</span><span class="special">;</span>
<span class="keyword">try</span> <span class="special">{</span>
<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>
<span class="identifier">p</span> <span class="special">=</span> <span class="identifier">f</span><span class="special">();</span>
<span class="comment">// `f` goes out of scope</span>
<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>
<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>
<span class="special">}</span>
<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>
<span class="comment">// crashes here</span>
<span class="special">}</span>
</pre>
</li>
<li class="listitem">
<span class="bold"><strong>Fix:</strong></span> In that particular example the problem
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>.
It keeps a type erased deleter, code for that deleter is located in plugin.
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>
attempts to call that deleter, however the plugin was already unloaded
and the code for deleter is not available any more.
</li>
<li class="listitem">
<span class="bold"><strong>Rule of thumb:</strong></span>: if your plugin method
returns any C++ class variable, then make sure that the plugin is loaded
until that variable and any of its copies are in scope.
</li>
<li class="listitem">
<span class="bold"><strong>Typical classes that cause such errors are:</strong></span>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
<code class="computeroutput"><span class="identifier">any</span></code>
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">function</span></code>
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">shared_ptr</span></code>
</li>
<li class="listitem">
any container with polymorphic allocator
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">type_index</span></code>
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">type_info</span></code>
</li>
<li class="listitem">
<code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">exception_ptr</span></code>
</li>
<li class="listitem">
<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>
holding a <code class="computeroutput"><span class="identifier">Derived</span></code>
type from plugin
</li>
<li class="listitem">
exception classes thrown from plugin
</li>
</ul></div>
</li>
</ul></div>
<pre class="programlisting"></pre>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<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<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
</p>
</div></td>
</tr></table>
<hr>
<div class="spirit-nav">
<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>
</div>
</body>
</html>
|
