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>F.A.Q.</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="limitations.html" title="Limitations"> 11<link rel="next" href="design_rationale.html" title="Design Rationale"> 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="limitations.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="design_rationale.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.f_a_q_"></a><a class="link" href="f_a_q_.html" title="F.A.Q.">F.A.Q.</a> 29</h2></div></div></div> 30<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 31 <span class="bold"><strong>Question:</strong></span> Is Boost.DLL thread-safe? 32 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "><li class="listitem"> 33 <span class="bold"><strong>Answer:</strong></span> Some platforms allow concurrent 34 calls to <code class="computeroutput"><span class="identifier">dlopen</span></code> like 35 functions. For those platforms Boost.DLL is safe in the manner as 36 all the C++ Standard Library containers are: it is safe to use different 37 instances of shared_library from different threads even if all the 38 instances loaded the same library. On other platforms it is not safe 39 to concurrently call any of the functions from Boost.DLL (even a 40 <code class="computeroutput"><span class="identifier">shared_library</span><span class="special">::</span><span class="identifier">location</span><span class="special">()</span></code> 41 call triggers a race condition). See <a class="link" href="limitations.html#boost_dll.limitations.multithread" title="Thread safe library loading (Fails on FreeBSD, MacOS, iOS and some other)">Limitations, 42 Thread safe library loading</a>. 43 </li></ul></div> 44 </li></ul></div> 45<pre class="programlisting"></pre> 46<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 47 <span class="bold"><strong>Question:</strong></span> Why on Linux symbols from one 48 plugin are seen in another? Can't get symbol with same name from right 49 plugin! 50 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "><li class="listitem"> 51 <span class="bold"><strong>Answer:</strong></span> You've run into the symbol 52 shadowing problem. Compile your plugins with "-fvisibility=hidden" 53 flag and take a look to the Tutorial section. 54 </li></ul></div> 55 </li></ul></div> 56<pre class="programlisting"></pre> 57<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 58 <span class="bold"><strong>Question:</strong></span> How Unicode (Windows) is handled? 59 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "><li class="listitem"> 60 <span class="bold"><strong>Answer:</strong></span> Boost.DLL supports Unicode, 61 so that you could provide Unicode paths to it. 62 </li></ul></div> 63 </li></ul></div> 64<pre class="programlisting"></pre> 65<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 66 <span class="bold"><strong>Question:</strong></span> Can I open an executable file? 67 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "><li class="listitem"> 68 <span class="bold"><strong>Answer:</strong></span> Yes, you can. Symbols need 69 be exported using in the executable using <code class="computeroutput"><span class="identifier">BOOST_SYMBOL_EXPORT</span></code> 70 or <code class="computeroutput"><span class="identifier">BOOST_DLL_ALIAS</span></code>. 71 You can call <code class="computeroutput"><span class="identifier">shared_library</span><span class="special">(</span><span class="identifier">program_location</span><span class="special">())</span></code> to load yourself. Refer to the 72 Tutorial section for more info. You can also query executables, just 73 provide a path to the executable to <code class="computeroutput"><span class="identifier">library_info</span></code> 74 class. 75 </li></ul></div> 76 </li></ul></div> 77<pre class="programlisting"></pre> 78<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 79 <span class="bold"><strong>Question:</strong></span> What if I specify wrong type 80 in <code class="computeroutput"><span class="identifier">shared_library</span><span class="special">::</span><span class="identifier">get</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> 81 or <code class="computeroutput"><span class="identifier">import</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>? 82 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "><li class="listitem"> 83 <span class="bold"><strong>Answer:</strong></span> Usually you'll end up with 84 <code class="computeroutput"><span class="identifier">Segmentation</span> <span class="identifier">Fault</span></code>. 85 However it is safe to make types more strict, for example making 86 <code class="computeroutput"><span class="keyword">const</span> <span class="keyword">int</span></code> 87 from an <code class="computeroutput"><span class="keyword">int</span></code> will not 88 harm. 89 </li></ul></div> 90 </li></ul></div> 91<pre class="programlisting"></pre> 92<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 93 <span class="bold"><strong>Question:</strong></span> Does your library guarantee 94 ABI stability of methods? 95 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "><li class="listitem"> 96 <span class="bold"><strong>Answer:</strong></span> Library only guarantees 97 that alias names created using the <code class="computeroutput"><span class="identifier">BOOST_DLL_ALIAS</span></code> 98 macros will not change with the change of compiler or platform. You 99 must take care of functions ABI and API stability by your own. 100 </li></ul></div> 101 </li></ul></div> 102<pre class="programlisting"></pre> 103<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 104 <span class="bold"><strong>Question:</strong></span> Are there any function signature 105 restrictions for the exported/imported functions? 106 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "><li class="listitem"> 107 <span class="bold"><strong>Answer:</strong></span> No. You may import/export 108 functions with any signature and any return parameter. 109 </li></ul></div> 110 </li></ul></div> 111<pre class="programlisting"></pre> 112<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 113 <span class="bold"><strong>Question:</strong></span> I have 2 plugins that use same 114 shared library. Would be the shared library loaded twice? 115 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "><li class="listitem"> 116 <span class="bold"><strong>Answer:</strong></span> No. Pugins will share the 117 shared library instance. 118 </li></ul></div> 119 </li></ul></div> 120<pre class="programlisting"></pre> 121<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 122 <span class="bold"><strong>Question:</strong></span> I have 2 plugins each of them 123 must work with it's own version of <code class="computeroutput"><span class="identifier">libsome_library</span></code> 124 shared library. How to achieve that? 125 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "><li class="listitem"> 126 <span class="bold"><strong>Answer:</strong></span> Avoid such situations by 127 statically linking in the libsome_library into each plugin and loading 128 plugins with <code class="computeroutput"><span class="identifier">load_mode</span><span class="special">::</span><span class="identifier">rtld_deepbind</span></code>. 129 </li></ul></div> 130 </li></ul></div> 131<pre class="programlisting"></pre> 132<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 133 <span class="bold"><strong>Question:</strong></span> How to load a shared object 134 from memory?? 135 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "><li class="listitem"> 136 <span class="bold"><strong>Answer:</strong></span> All existing OS avoid loading 137 shared libraries directly from userspace memory, so you'll find no 138 syscall for such case. Currently Boost.DLL provides no means for 139 honest loading shared objects from memory. This requires reimplementing 140 dynamic linker logic in userspace for all the platforms, which is 141 a huge amount of work and very error-prone. However working patches 142 are welcomed! 143 </li></ul></div> 144 </li></ul></div> 145<p> 146 Workaround would be to write plugin into a temporary file in RAM and load plugin 147 from it: 148</p> 149<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">filesystem</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 150<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">dll</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span> 151<span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">;</span> 152 153<span class="identifier">dll</span><span class="special">:</span><span class="identifier">shared_library</span> <span class="identifier">load_from_memory</span><span class="special">(</span><span class="keyword">unsigned</span> <span class="keyword">char</span><span class="special">*</span> <span class="identifier">data</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">size_t</span> <span class="identifier">size</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">filesystem</span><span class="special">::</span><span class="identifier">path</span><span class="special">&</span> <span class="identifier">tmp_plugin_path</span> <span class="special">=</span> <span class="identifier">filesystem</span><span class="special">::</span><span class="identifier">unique_path</span><span class="special">()</span> <span class="special">/</span> <span class="string">"libplugin.so"</span><span class="special">)</span> <span class="special">{</span> 154 <span class="keyword">const</span> <span class="identifier">filesystem</span><span class="special">::</span><span class="identifier">path</span> <span class="identifier">plugin_location</span> <span class="special">=</span> <span class="identifier">filesystem</span><span class="special">::</span><span class="identifier">temp_directory_path</span><span class="special">()</span> <span class="special">/</span> <span class="identifier">tmp_plugin_path</span><span class="special">;</span> 155 <span class="identifier">filesystem</span><span class="special">::</span><span class="identifier">create_directories</span><span class="special">(</span><span class="identifier">plugin_location</span><span class="special">.</span><span class="identifier">parent_path</span><span class="special">());</span> 156 <span class="identifier">filesystem</span><span class="special">::</span><span class="identifier">ofstream</span> <span class="identifier">ofs</span><span class="special">(</span><span class="identifier">plugin_location</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">ios</span><span class="special">::</span><span class="identifier">out</span><span class="special">|</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">ios</span><span class="special">::</span><span class="identifier">bin</span><span class="special">|</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">ios</span><span class="special">::</span><span class="identifier">trunc</span><span class="special">);</span> 157 <span class="identifier">ofs</span><span class="special">.</span><span class="identifier">write</span><span class="special">(</span><span class="identifier">data</span><span class="special">,</span> <span class="identifier">size</span><span class="special">);</span> 158 159 <span class="keyword">return</span> <span class="identifier">dll</span><span class="special">::</span><span class="identifier">shared_library</span><span class="special">(</span><span class="identifier">plugin_location</span><span class="special">);</span> 160<span class="special">}</span> 161</pre> 162<p> 163 </p> 164<p> 165 But there's no guarantee that <code class="computeroutput"><span class="identifier">filesystem</span><span class="special">::</span><span class="identifier">temp_directory_path</span><span class="special">()</span></code> will actually write to RAM, that's very platform 166 dependent. 167 </p> 168<pre class="programlisting"></pre> 169<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"> 170 <span class="bold"><strong>Question:</strong></span> I have found a bug, how do I 171 notify? 172 <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; "><li class="listitem"> 173 <span class="bold"><strong>Answer:</strong></span> Create an <a href="https://github.com/apolukhin/Boost.DLL/issues" target="_top">issue 174 at GitHub</a> with a detailed description. 175 </li></ul></div> 176 </li></ul></div> 177</div> 178<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 179<td align="left"></td> 180<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> 181 Distributed under the Boost Software License, Version 1.0. (See accompanying 182 file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) 183 </p> 184</div></td> 185</tr></table> 186<hr> 187<div class="spirit-nav"> 188<a accesskey="p" href="limitations.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="design_rationale.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 189</div> 190</body> 191</html> 192