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<div id="projectname">Crypto++
 <span id="projectnumber">7.0</span>
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<div id="projectbrief">Free C++ class library of cryptographic schemes</div>
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<a href="#pub-methods">Public Member Functions</a> |
<a href="class_singleton-members.html">List of all members</a> </div>
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<div class="title">Singleton< T, F, instance > Class Template Reference</div> </div>
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<p>Restricts the instantiation of a class to one static object without locks.
<a href="class_singleton.html#details">More...</a></p>
<table class="memberdecls">
<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="pub-methods"></a>
Public Member Functions</h2></td></tr>
<tr class="memitem:a864479413a63f1752a16981a4819a123"><td class="memItemLeft" align="right" valign="top"><a id="a864479413a63f1752a16981a4819a123"></a>
 </td><td class="memItemRight" valign="bottom"><b>Singleton</b> (F objectFactory=F())</td></tr>
<tr class="separator:a864479413a63f1752a16981a4819a123"><td class="memSeparator" colspan="2"> </td></tr>
<tr class="memitem:a2dfafdfafaaf20ca4cfc550125f6332d"><td class="memItemLeft" align="right" valign="top">const T & </td><td class="memItemRight" valign="bottom"><a class="el" href="class_singleton.html#a2dfafdfafaaf20ca4cfc550125f6332d">Ref</a> (...) const</td></tr>
<tr class="memdesc:a2dfafdfafaaf20ca4cfc550125f6332d"><td class="mdescLeft"> </td><td class="mdescRight">Return a reference to the inner <a class="el" href="class_singleton.html" title="Restricts the instantiation of a class to one static object without locks. ">Singleton</a> object. <a href="#a2dfafdfafaaf20ca4cfc550125f6332d">More...</a><br /></td></tr>
<tr class="separator:a2dfafdfafaaf20ca4cfc550125f6332d"><td class="memSeparator" colspan="2"> </td></tr>
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<a name="details" id="details"></a><h2 class="groupheader">Detailed Description</h2>
<div class="textblock"><h3>template<class T, class F = NewObject<T>, int instance = 0><br />
class Singleton< T, F, instance ></h3>
<p>Restricts the instantiation of a class to one static object without locks. </p>
<dl class="tparams"><dt>Template Parameters</dt><dd>
<table class="tparams">
<tr><td class="paramname">T</td><td>the class or type </td></tr>
<tr><td class="paramname">F</td><td>the object factory for T </td></tr>
<tr><td class="paramname">instance</td><td>an instance counter for the class object</td></tr>
</table>
</dd>
</dl>
<p>This class safely initializes a static object in a multithreaded environment. For C++03 and below it will do so without using locks for portability. If two threads call <a class="el" href="class_singleton.html#a2dfafdfafaaf20ca4cfc550125f6332d" title="Return a reference to the inner Singleton object. ">Ref()</a> at the same time, they may get back different references, and one object may end up being memory leaked. This is by design and it avoids a subltle initialization problem ina multithreaded environment with thread local storage on early Windows platforms, like Windows XP and Windows 2003.</p>
<p>For C++11 and above, a standard double-checked locking pattern with thread fences are used. The locks and fences are standard and do not hinder portability.</p>
<p>Microsoft's C++11 implementation provides the necessary primitive support on Windows Vista and above when using Visual Studio 2015 (<code>cl.exe</code> version 19.00). If C++11 is desired, you should set <code>WINVER</code> or <code>_WIN32_WINNT</code> to 0x600 (or above), and compile with Visual Studio 2015. </p><dl class="section see"><dt>See also</dt><dd><a href="http://preshing.com/20130930/double-checked-locking-is-fixed-in-cpp11/">Double-Checked Locking is Fixed In C++11</a>, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2008/n2660.htm">Dynamic Initialization and Destruction with Concurrency</a> and <a href="http://msdn.microsoft.com/en-us/library/6yh4a9k1.aspx">Thread Local Storage (TLS)</a> on MSDN. </dd></dl>
<dl class="section since"><dt>Since</dt><dd>Crypto++ 5.2 </dd></dl>
<p class="definition">Definition at line <a class="el" href="misc_8h_source.html#l00291">291</a> of file <a class="el" href="misc_8h_source.html">misc.h</a>.</p>
</div><h2 class="groupheader">Member Function Documentation</h2>
<a id="a2dfafdfafaaf20ca4cfc550125f6332d"></a>
<h2 class="memtitle"><span class="permalink"><a href="#a2dfafdfafaaf20ca4cfc550125f6332d">◆ </a></span>Ref()</h2>
<div class="memitem">
<div class="memproto">
<div class="memtemplate">
template<class T , class F , int instance> </div>
<table class="memname">
<tr>
<td class="memname">const T & <a class="el" href="class_singleton.html">Singleton</a>< T, F, instance >::Ref </td>
<td>(</td>
<td class="paramtype"> </td>
<td class="paramname"><em>...</em></td><td>)</td>
<td> const</td>
</tr>
</table>
</div><div class="memdoc">
<p>Return a reference to the inner <a class="el" href="class_singleton.html" title="Restricts the instantiation of a class to one static object without locks. ">Singleton</a> object. </p>
<dl class="tparams"><dt>Template Parameters</dt><dd>
<table class="tparams">
<tr><td class="paramname">T</td><td>the class or type </td></tr>
<tr><td class="paramname">F</td><td>the object factory for T </td></tr>
<tr><td class="paramname">instance</td><td>an instance counter for the class object</td></tr>
</table>
</dd>
</dl>
<p><a class="el" href="class_singleton.html#a2dfafdfafaaf20ca4cfc550125f6332d" title="Return a reference to the inner Singleton object. ">Ref()</a> is used to create the object using the object factory. The object is only created once with the limitations discussed in the class documentation. </p><dl class="section see"><dt>See also</dt><dd><a href="http://preshing.com/20130930/double-checked-locking-is-fixed-in-cpp11/">Double-Checked Locking is Fixed In C++11</a> </dd></dl>
<dl class="section since"><dt>Since</dt><dd>Crypto++ 5.2 </dd></dl>
<p class="definition">Definition at line <a class="el" href="misc_8h_source.html#l00312">312</a> of file <a class="el" href="misc_8h_source.html">misc.h</a>.</p>
</div>
</div>
<hr/>The documentation for this class was generated from the following file:<ul>
<li><a class="el" href="misc_8h_source.html">misc.h</a></li>
</ul>
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