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            <h1>XSLoader</h1>


  <!--    -->
<ul><li><a href="#NAME">NAME</a><li><a href="#VERSION">VERSION</a><li><a href="#SYNOPSIS">SYNOPSIS</a><li><a href="#DESCRIPTION">DESCRIPTION</a><ul><li><a href="#Migration-from-DynaLoader">Migration from DynaLoader</a><li><a href="#Backward-compatible-boilerplate">Backward compatible boilerplate</a></ul><li><a href="#Order-of-initialization%3a-early-load()">Order of initialization: early load()</a><ul><li><a href="#The-most-hairy-case">The most hairy case</a></ul><li><a href="#DIAGNOSTICS">DIAGNOSTICS</a><li><a href="#LIMITATIONS">LIMITATIONS</a><li><a href="#KNOWN-BUGS">KNOWN BUGS</a><li><a href="#BUGS">BUGS</a><li><a href="#SEE-ALSO">SEE ALSO</a><li><a href="#AUTHORS">AUTHORS</a><li><a href="#COPYRIGHT-%26-LICENSE">COPYRIGHT & LICENSE</a></ul><a name="NAME"></a><h1>NAME</h1>
<p>XSLoader - Dynamically load C libraries into Perl code</p>
<a name="VERSION"></a><h1>VERSION</h1>
<p>Version 0.24</p>
<a name="SYNOPSIS"></a><h1>SYNOPSIS</h1>
<pre class="verbatim"><ol><li><a name="package-YourPackage"></a>    package <span class="i">YourPackage</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/require.html">require</a> <span class="w">XSLoader</span><span class="sc">;</span></li><li></li><li>    <span class="i">XSLoader::load</span><span class="s">(</span><span class="s">)</span><span class="sc">;</span></li></ol></pre><a name="DESCRIPTION"></a><h1>DESCRIPTION</h1>
<p>This module defines a standard <i>simplified</i> interface to the dynamic
linking mechanisms available on many platforms.  Its primary purpose is
to implement cheap automatic dynamic loading of Perl modules.</p>
<p>For a more complicated interface, see <a href="DynaLoader.html">DynaLoader</a>.  Many (most)
features of <code class="inline"><span class="w">DynaLoader</span></code>
 are not implemented in <code class="inline"><span class="w">XSLoader</span></code>
, like for
example the <code class="inline"><span class="w">dl_load_flags</span></code>
, not honored by <code class="inline"><span class="w">XSLoader</span></code>
.</p>
<a name="Migration-from-DynaLoader"></a><h2>Migration from <code class="inline"><span class="w">DynaLoader</span></code>
</h2>
<p>A typical module using <a href="DynaLoader.html">DynaLoader</a> starts like this:</p>
<pre class="verbatim"><ol><li><a name="package-YourPackage"></a>    package <span class="i">YourPackage</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/require.html">require</a> <span class="w">DynaLoader</span><span class="sc">;</span></li><li></li><li>    <a class="l_k" href="functions/our.html">our</a> <span class="i">@ISA</span> = <span class="q">qw( OnePackage OtherPackage DynaLoader )</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/our.html">our</a> <span class="i">$VERSION</span> = <span class="q">&#39;0.01&#39;</span><span class="sc">;</span></li><li>    <span class="w">bootstrap</span> <span class="w">YourPackage</span> <span class="i">$VERSION</span><span class="sc">;</span></li></ol></pre><p>Change this to</p>
<pre class="verbatim"><ol><li><a name="package-YourPackage"></a>    package <span class="i">YourPackage</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/use.html">use</a> <span class="w">XSLoader</span><span class="sc">;</span></li><li></li><li>    <a class="l_k" href="functions/our.html">our</a> <span class="i">@ISA</span> = <span class="q">qw( OnePackage OtherPackage )</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/our.html">our</a> <span class="i">$VERSION</span> = <span class="q">&#39;0.01&#39;</span><span class="sc">;</span></li><li>    <span class="w">XSLoader::load</span> <span class="q">&#39;YourPackage&#39;</span><span class="cm">,</span> <span class="i">$VERSION</span><span class="sc">;</span></li></ol></pre><p>In other words: replace <code class="inline"><a class="l_k" href="functions/require.html">require</a> <span class="w">DynaLoader</span></code>
 by <code class="inline"><a class="l_k" href="functions/use.html">use</a> <span class="w">XSLoader</span></code>
, remove
<code class="inline"><span class="w">DynaLoader</span></code>
 from <code class="inline"><span class="i">@ISA</span></code>
, change <code class="inline"><span class="w">bootstrap</span></code>
 by <code class="inline"><span class="w">XSLoader::load</span></code>
.  Do not
forget to quote the name of your package on the <code class="inline"><span class="w">XSLoader::load</span></code>
 line,
and add comma (<code class="inline"><span class="cm">,</span></code>
) before the arguments (<code class="inline"><span class="i">$VERSION</span></code>
 above).</p>
<p>Of course, if <code class="inline"><span class="i">@ISA</span></code>
 contained only <code class="inline"><span class="w">DynaLoader</span></code>
, there is no need to have
the <code class="inline"><span class="i">@ISA</span></code>
 assignment at all; moreover, if instead of <code class="inline"><a class="l_k" href="functions/our.html">our</a></code> one uses the
more backward-compatible</p>
<pre class="verbatim"><ol><li>    <a class="l_k" href="functions/use.html">use</a> <span class="w">vars</span> <span class="q">qw($VERSION @ISA)</span><span class="sc">;</span></li></ol></pre><p>one can remove this reference to <code class="inline"><span class="i">@ISA</span></code>
 together with the <code class="inline"><span class="i">@ISA</span></code>
 assignment.</p>
<p>If no <code class="inline"><span class="i">$VERSION</span></code>
 was specified on the <code class="inline"><span class="w">bootstrap</span></code>
 line, the last line becomes</p>
<pre class="verbatim"><ol><li>    <span class="w">XSLoader::load</span> <span class="q">&#39;YourPackage&#39;</span><span class="sc">;</span></li></ol></pre><p>If the call to <code class="inline"><span class="w">load</span></code>
 is from <code class="inline"><span class="w">YourPackage</span></code>
, then that can be further
simplified to</p>
<pre class="verbatim"><ol><li>    <span class="i">XSLoader::load</span><span class="s">(</span><span class="s">)</span><span class="sc">;</span></li></ol></pre><p>as <code class="inline"><span class="w">load</span></code>
 will use <code class="inline"><a class="l_k" href="functions/caller.html">caller</a></code> to determine the package.</p>
<a name="Backward-compatible-boilerplate"></a><h2>Backward compatible boilerplate</h2>
<p>If you want to have your cake and eat it too, you need a more complicated
boilerplate.</p>
<pre class="verbatim"><ol><li><a name="package-YourPackage"></a>    package <span class="i">YourPackage</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/use.html">use</a> <span class="w">vars</span> <span class="q">qw($VERSION @ISA)</span><span class="sc">;</span></li><li></li><li>    <span class="i">@ISA</span> = <span class="q">qw( OnePackage OtherPackage )</span><span class="sc">;</span></li><li>    <span class="i">$VERSION</span> = <span class="q">&#39;0.01&#39;</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/eval.html">eval</a> <span class="s">{</span></li><li>       <a class="l_k" href="functions/require.html">require</a> <span class="w">XSLoader</span><span class="sc">;</span></li><li>       <span class="i">XSLoader::load</span><span class="s">(</span><span class="q">&#39;YourPackage&#39;</span><span class="cm">,</span> <span class="i">$VERSION</span><span class="s">)</span><span class="sc">;</span></li><li>       <span class="n">1</span><span class="sc">;</span></li><li>    <span class="s">}</span> or <a class="l_k" href="functions/do.html">do</a> <span class="s">{</span></li><li>       <a class="l_k" href="functions/require.html">require</a> <span class="w">DynaLoader</span><span class="sc">;</span></li><li>       <a class="l_k" href="functions/push.html">push</a> <span class="i">@ISA</span><span class="cm">,</span> <span class="q">&#39;DynaLoader&#39;</span><span class="sc">;</span></li><li>       <span class="w">bootstrap</span> <span class="w">YourPackage</span> <span class="i">$VERSION</span><span class="sc">;</span></li><li>    <span class="s">}</span><span class="sc">;</span></li></ol></pre><p>The parentheses about <code class="inline"><span class="i">XSLoader::load</span><span class="s">(</span><span class="s">)</span></code>
 arguments are needed since we replaced
<code class="inline"><a class="l_k" href="functions/use.html">use</a> <span class="w">XSLoader</span></code>
 by <code class="inline"><a class="l_k" href="functions/require.html">require</a></code>, so the compiler does not know that a function
<code class="inline"><span class="i">XSLoader::load</span><span class="s">(</span><span class="s">)</span></code>
 is present.</p>
<p>This boilerplate uses the low-overhead <code class="inline"><span class="w">XSLoader</span></code>
 if present; if used with
an antique Perl which has no <code class="inline"><span class="w">XSLoader</span></code>
, it falls back to using <code class="inline"><span class="w">DynaLoader</span></code>
.</p>
<a name="Order-of-initialization%3a-early-load()"></a><h1>Order of initialization: early load()</h1>
<p><i>Skip this section if the XSUB functions are supposed to be called from other
modules only; read it only if you call your XSUBs from the code in your module,
or have a <code class="inline"><span class="j">BOOT:</span></code>
 section in your XS file (see <a href="perlxs.html#The-BOOT%3a-Keyword">The BOOT: Keyword in perlxs</a>).
What is described here is equally applicable to the <a href="DynaLoader.html">DynaLoader</a>
interface.</i></p>
<p>A sufficiently complicated module using XS would have both Perl code (defined
in <i>YourPackage.pm</i>) and XS code (defined in <i>YourPackage.xs</i>).  If this
Perl code makes calls into this XS code, and/or this XS code makes calls to
the Perl code, one should be careful with the order of initialization.</p>
<p>The call to <code class="inline"><span class="i">XSLoader::load</span><span class="s">(</span><span class="s">)</span></code>
 (or <code class="inline"><span class="i">bootstrap</span><span class="s">(</span><span class="s">)</span></code>
) calls the module's
bootstrap code. For modules build by <i>xsubpp</i> (nearly all modules) this
has three side effects:</p>
<ul>
<li>
<p>A sanity check is done to ensure that the versions of the <i>.pm</i> and the
(compiled) <i>.xs</i> parts are compatible. If <code class="inline"><span class="i">$VERSION</span></code>
 was specified, this
is used for the check. If not specified, it defaults to
<code class="inline"><span class="i">$XS_VERSION</span> // <span class="i">$VERSION</span></code>
 (in the module's namespace)</p>
</li>
<li>
<p>the XSUBs are made accessible from Perl</p>
</li>
<li>
<p>if a <code class="inline"><span class="j">BOOT:</span></code>
 section was present in the <i>.xs</i> file, the code there is called.</p>
</li>
</ul>
<p>Consequently, if the code in the <i>.pm</i> file makes calls to these XSUBs, it is
convenient to have XSUBs installed before the Perl code is defined; for
example, this makes prototypes for XSUBs visible to this Perl code.
Alternatively, if the <code class="inline"><span class="j">BOOT:</span></code>
 section makes calls to Perl functions (or
uses Perl variables) defined in the <i>.pm</i> file, they must be defined prior to
the call to <code class="inline"><span class="i">XSLoader::load</span><span class="s">(</span><span class="s">)</span></code>
 (or <code class="inline"><span class="i">bootstrap</span><span class="s">(</span><span class="s">)</span></code>
).</p>
<p>The first situation being much more frequent, it makes sense to rewrite the
boilerplate as</p>
<pre class="verbatim"><ol><li><a name="package-YourPackage"></a>    package <span class="i">YourPackage</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/use.html">use</a> <span class="w">XSLoader</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/use.html">use</a> <span class="w">vars</span> <span class="q">qw($VERSION @ISA)</span><span class="sc">;</span></li><li></li><li>    BEGIN <span class="s">{</span></li><li>       <span class="i">@ISA</span> = <span class="q">qw( OnePackage OtherPackage )</span><span class="sc">;</span></li><li>       <span class="i">$VERSION</span> = <span class="q">&#39;0.01&#39;</span><span class="sc">;</span></li><li></li><li>       <span class="c"># Put Perl code used in the BOOT: section here</span></li><li></li><li>       <span class="w">XSLoader::load</span> <span class="q">&#39;YourPackage&#39;</span><span class="cm">,</span> <span class="i">$VERSION</span><span class="sc">;</span></li><li>    <span class="s">}</span></li><li></li><li>    <span class="c"># Put Perl code making calls into XSUBs here</span></li></ol></pre><a name="The-most-hairy-case"></a><h2>The most hairy case</h2>
<p>If the interdependence of your <code class="inline"><span class="j">BOOT:</span></code>
 section and Perl code is
more complicated than this (e.g., the <code class="inline"><span class="j">BOOT:</span></code>
 section makes calls to Perl
functions which make calls to XSUBs with prototypes), get rid of the <code class="inline"><span class="j">BOOT:</span></code>

section altogether.  Replace it with a function <code class="inline"><span class="i">onBOOT</span><span class="s">(</span><span class="s">)</span></code>
, and call it like
this:</p>
<pre class="verbatim"><ol><li><a name="package-YourPackage"></a>    package <span class="i">YourPackage</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/use.html">use</a> <span class="w">XSLoader</span><span class="sc">;</span></li><li>    <a class="l_k" href="functions/use.html">use</a> <span class="w">vars</span> <span class="q">qw($VERSION @ISA)</span><span class="sc">;</span></li><li></li><li>    BEGIN <span class="s">{</span></li><li>       <span class="i">@ISA</span> = <span class="q">qw( OnePackage OtherPackage )</span><span class="sc">;</span></li><li>       <span class="i">$VERSION</span> = <span class="q">&#39;0.01&#39;</span><span class="sc">;</span></li><li>       <span class="w">XSLoader::load</span> <span class="q">&#39;YourPackage&#39;</span><span class="cm">,</span> <span class="i">$VERSION</span><span class="sc">;</span></li><li>    <span class="s">}</span></li><li></li><li>    <span class="c"># Put Perl code used in onBOOT() function here; calls to XSUBs are</span></li><li>    <span class="c"># prototype-checked.</span></li><li></li><li>    <span class="w">onBOOT</span><span class="sc">;</span></li><li></li><li>    <span class="c"># Put Perl initialization code assuming that XS is initialized here</span></li></ol></pre><a name="DIAGNOSTICS"></a><h1>DIAGNOSTICS</h1>
<ul>
<li><a name="Can't-find-'%25s'-symbol-in-%25s"></a><b><code class="inline">Can't find '%s' symbol in %s</code></b>
<p><b>(F)</b> The bootstrap symbol could not be found in the extension module.</p>
</li>
<li><a name="Can't-load-'%25s'-for-module-%25s%3a-%25s"></a><b><code class="inline">Can't load '%s' for module %s: %s</code></b>
<p><b>(F)</b> The loading or initialisation of the extension module failed.
The detailed error follows.</p>
</li>
<li><a name="Undefined-symbols-present-after-loading-%25s%3a-%25s"></a><b><code class="inline">Undefined symbols present after loading %s: %s</code></b>
<p><b>(W)</b> As the message says, some symbols stay undefined although the
extension module was correctly loaded and initialised. The list of undefined
symbols follows.</p>
</li>
</ul>
<a name="LIMITATIONS"></a><h1>LIMITATIONS</h1>
<p>To reduce the overhead as much as possible, only one possible location
is checked to find the extension DLL (this location is where <code class="inline"><span class="w">make</span> <span class="w">install</span></code>

would put the DLL).  If not found, the search for the DLL is transparently
delegated to <code class="inline"><span class="w">DynaLoader</span></code>
, which looks for the DLL along the <code class="inline"><span class="i">@INC</span></code>
 list.</p>
<p>In particular, this is applicable to the structure of <code class="inline"><span class="i">@INC</span></code>
 used for testing
not-yet-installed extensions.  This means that running uninstalled extensions
may have much more overhead than running the same extensions after
<code class="inline"><span class="w">make</span> <span class="w">install</span></code>
.</p>
<a name="KNOWN-BUGS"></a><h1>KNOWN BUGS</h1>
<p>The new simpler way to call <code class="inline"><span class="i">XSLoader::load</span><span class="s">(</span><span class="s">)</span></code>
 with no arguments at all
does not work on Perl 5.8.4 and 5.8.5.</p>
<a name="BUGS"></a><h1>BUGS</h1>
<p>Please report any bugs or feature requests via the perlbug(1) utility.</p>
<a name="SEE-ALSO"></a><h1>SEE ALSO</h1>
<p><a href="DynaLoader.html">DynaLoader</a></p>
<a name="AUTHORS"></a><h1>AUTHORS</h1>
<p>Ilya Zakharevich originally extracted <code class="inline"><span class="w">XSLoader</span></code>
 from <code class="inline"><span class="w">DynaLoader</span></code>
.</p>
<p>CPAN version is currently maintained by S&#xe9;bastien Aperghis-Tramoni
&lt;sebastien@aperghis.net&gt;.</p>
<p>Previous maintainer was Michael G Schwern &lt;schwern@pobox.com&gt;.</p>
<a name="COPYRIGHT-%26-LICENSE"></a><h1>COPYRIGHT &amp; LICENSE</h1>
<p>Copyright (C) 1990-2011 by Larry Wall and others.</p>
<p>This program is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.</p>




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