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<a href="#pub-methods">Public Member Functions</a> |
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<a href="../../da/d44/class_m_utils_1_1_lazy-members.html">List of all members</a> </div>
<div class="headertitle">
-<div class="title">MUtils::Lazy< T > Class Template Reference<span class="mlabels"><span class="mlabel">abstract</span></span></div> </div>
+<div class="title">MUtils::Lazy< T > Class Template Reference</div> </div>
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<tr class="heading"><td colspan="2"><h2 class="groupheader"><a name="pub-methods"></a>
Public Member Functions</h2></td></tr>
+<tr class="memitem:a7dc7baa7d7ac31c644965be2ccc4d8cd"><td class="memItemLeft" align="right" valign="top"><a id="a7dc7baa7d7ac31c644965be2ccc4d8cd"></a>
+ </td><td class="memItemRight" valign="bottom"><b>Lazy</b> (std::function< T *(void)> &&initializer)</td></tr>
+<tr class="separator:a7dc7baa7d7ac31c644965be2ccc4d8cd"><td class="memSeparator" colspan="2"> </td></tr>
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T & </td><td class="memItemRight" valign="bottom"><b>operator*</b> (void)</td></tr>
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-Protected Member Functions</h2></td></tr>
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-virtual T * </td><td class="memItemRight" valign="bottom"><b>create</b> ()=0</td></tr>
-<tr class="separator:a03f52adf0e421b20298f2f7578e3375f"><td class="memSeparator" colspan="2"> </td></tr>
</table>
<a name="details" id="details"></a><h2 class="groupheader">Detailed Description</h2>
<div class="textblock"><h3>template<typename T><br />
class MUtils::Lazy< T ></h3>
<p><a class="el" href="../../d0/dce/class_m_utils_1_1_lazy.html" title="Lazy initialization template class. ">Lazy</a> initialization template class. </p>
-<p>In order to create your own "lazy" initializer, inherit from the <code><a class="el" href="../../d0/dce/class_m_utils_1_1_lazy.html" title="Lazy initialization template class. ">Lazy</a><T></code> class an implement the <a class="el" href="../../d2/dad/_hash_8h.html#a330b73d6927d6cd95892712f9396f40e" title="Create instance of a hash function. ">create()</a> function. The lazy-initialized value can be obtained from a <code><a class="el" href="../../d0/dce/class_m_utils_1_1_lazy.html" title="Lazy initialization template class. ">Lazy</a><T></code> instance by using the <code>operator*()</code>. Initialization of the value happens when the <code>operator*()</code> is called for the very first time, by invoking the concrete <a class="el" href="../../d2/dad/_hash_8h.html#a330b73d6927d6cd95892712f9396f40e" title="Create instance of a hash function. ">create()</a> function. The return value of <a class="el" href="../../d2/dad/_hash_8h.html#a330b73d6927d6cd95892712f9396f40e" title="Create instance of a hash function. ">create()</a> is then stored internally, so that any subsequent call to the <code>operator*()</code> immediately returns the previously created value.</p>
-<p><b>Note on thread-saftey:</b> This class is thread-safe in the sense that all calls to <code>operator*()</code> on the same <code><a class="el" href="../../d0/dce/class_m_utils_1_1_lazy.html" title="Lazy initialization template class. ">Lazy</a><T></code> instance, regardless from which thread, are guaranteed to return the exactly same value/object. Still, if the value has <em>not</em> been initialized yet <b>and</b> if multiple threads happen to call <code>operator*()</code> at the same time, then the concrete <a class="el" href="../../d2/dad/_hash_8h.html#a330b73d6927d6cd95892712f9396f40e" title="Create instance of a hash function. ">create()</a> function <em>may</em> be invoked more than once (concurrently and by different threads). In that case, all but one return value of <a class="el" href="../../d2/dad/_hash_8h.html#a330b73d6927d6cd95892712f9396f40e" title="Create instance of a hash function. ">create()</a> are discarded, and all threads eventually receive the same value/object. </p>
+<p>The lazy-initialized value of type T can be obtained from a <code><a class="el" href="../../d0/dce/class_m_utils_1_1_lazy.html" title="Lazy initialization template class. ">Lazy</a><T></code> instance by using the <code>operator*()</code>. Initialization of the value happens when the <code>operator*()</code> is called for the very first time, by invoking the <code>initializer</code> lambda-function that was passed to the constructor. The return value of the <code>initializer</code> lambda-function is then stored internally, so that any subsequent call to the <code>operator*()</code> <em>immediately</em> returns the previously created value.</p>
+<p><b>Note on thread-saftey:</b> This class is thread-safe in the sense that all calls to <code>operator*()</code> on the same <code><a class="el" href="../../d0/dce/class_m_utils_1_1_lazy.html" title="Lazy initialization template class. ">Lazy</a><T></code> instance, regardless from which thread, are guaranteed to return the exactly same value/object. Still, if the value has <em>not</em> been initialized yet <b>and</b> if multiple threads happen to call <code>operator*()</code> at the same time, then the <code>initializer</code> lambda-function <em>may</em> be invoked more than once (concurrently and by different threads). In that case, all but one return value of the <code>initializer</code> lambda-function are discarded, and all threads eventually obtain the same value/object. </p>
</div><hr/>The documentation for this class was generated from the following file:<ul>
<li>include/MUtils/<a class="el" href="../../d8/d4d/_lazy_8h_source.html">Lazy.h</a></li>
</ul>
<a href="#details">More...</a></p>
<div class="textblock"><code>#include <<a class="el" href="../../d5/d3b/_global_8h_source.html">MUtils/Global.h</a>></code><br />
<code>#include <MUtils/Exception.h></code><br />
-<code>#include <QScopedPointer></code><br />
<code>#include <QAtomicPointer></code><br />
+<code>#include <functional></code><br />
</div>
<p><a href="../../d8/d4d/_lazy_8h_source.html">Go to the source code of this file.</a></p>
<table class="memberdecls">
<div class="title">Lazy.h</div> </div>
</div><!--header-->
<div class="contents">
-<a href="../../d8/d4d/_lazy_8h.html">Go to the documentation of this file.</a><div class="fragment"><div class="line"><a name="l00001"></a><span class="lineno"> 1</span> <span class="comment">// MuldeR's Utilities for Qt</span></div><div class="line"><a name="l00003"></a><span class="lineno"> 3</span> <span class="comment">// Copyright (C) 2004-2017 LoRd_MuldeR <MuldeR2@GMX.de></span></div><div class="line"><a name="l00004"></a><span class="lineno"> 4</span> <span class="comment">//</span></div><div class="line"><a name="l00005"></a><span class="lineno"> 5</span> <span class="comment">// This library is free software; you can redistribute it and/or</span></div><div class="line"><a name="l00006"></a><span class="lineno"> 6</span> <span class="comment">// modify it under the terms of the GNU Lesser General Public</span></div><div class="line"><a name="l00007"></a><span class="lineno"> 7</span> <span class="comment">// License as published by the Free Software Foundation; either</span></div><div class="line"><a name="l00008"></a><span class="lineno"> 8</span> <span class="comment">// version 2.1 of the License, or (at your option) any later version.</span></div><div class="line"><a name="l00009"></a><span class="lineno"> 9</span> <span class="comment">//</span></div><div class="line"><a name="l00010"></a><span class="lineno"> 10</span> <span class="comment">// This library is distributed in the hope that it will be useful,</span></div><div class="line"><a name="l00011"></a><span class="lineno"> 11</span> <span class="comment">// but WITHOUT ANY WARRANTY; without even the implied warranty of</span></div><div class="line"><a name="l00012"></a><span class="lineno"> 12</span> <span class="comment">// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU</span></div><div class="line"><a name="l00013"></a><span class="lineno"> 13</span> <span class="comment">// Lesser General Public License for more details.</span></div><div class="line"><a name="l00014"></a><span class="lineno"> 14</span> <span class="comment">//</span></div><div class="line"><a name="l00015"></a><span class="lineno"> 15</span> <span class="comment">// You should have received a copy of the GNU Lesser General Public</span></div><div class="line"><a name="l00016"></a><span class="lineno"> 16</span> <span class="comment">// License along with this library; if not, write to the Free Software</span></div><div class="line"><a name="l00017"></a><span class="lineno"> 17</span> <span class="comment">// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA</span></div><div class="line"><a name="l00018"></a><span class="lineno"> 18</span> <span class="comment">//</span></div><div class="line"><a name="l00019"></a><span class="lineno"> 19</span> <span class="comment">// http://www.gnu.org/licenses/lgpl-2.1.txt</span></div><div class="line"><a name="l00021"></a><span class="lineno"> 21</span> <span class="comment"></span></div><div class="line"><a name="l00027"></a><span class="lineno"> 27</span> <span class="preprocessor">#pragma once</span></div><div class="line"><a name="l00028"></a><span class="lineno"> 28</span> </div><div class="line"><a name="l00029"></a><span class="lineno"> 29</span> <span class="comment">//MUtils</span></div><div class="line"><a name="l00030"></a><span class="lineno"> 30</span> <span class="preprocessor">#include <<a class="code" href="../../d5/d3b/_global_8h.html">MUtils/Global.h</a>></span></div><div class="line"><a name="l00031"></a><span class="lineno"> 31</span> <span class="preprocessor">#include <MUtils/Exception.h></span></div><div class="line"><a name="l00032"></a><span class="lineno"> 32</span> </div><div class="line"><a name="l00033"></a><span class="lineno"> 33</span> <span class="comment">//Qt</span></div><div class="line"><a name="l00034"></a><span class="lineno"> 34</span> <span class="preprocessor">#include <Q
ScopedPointer></span></div><div class="line"><a name="l00035"></a><span class="lineno"> 35</span> <span class="preprocessor">#include <QAtomicPointer></span></div><div class="line"><a name="l00036"></a><span class="lineno"> 36</span> </div><div class="line"><a name="l00037"></a><span class="lineno"> 37</span> <span class="keyword">namespace </span><a class="code" href="../../d3/da6/namespace_m_utils.html">MUtils</a></div><div class="line"><a name="l00038"></a><span class="lineno"> 38</span> {</div><div class="line"><a name="l00046"></a><span class="lineno"><a class="line" href="../../d0/dce/class_m_utils_1_1_lazy.html"> 46</a></span>  <span class="keyword">template</span><<span class="keyword">typename</span> T> <span class="keyword">class </span><a class="code" href="../../d0/dce/class_m_utils_1_1_lazy.html">Lazy</a></div><div class="line"><a name="l00047"></a><span class="lineno"> 47</span>  {</div><div class="line"><a name="l00048"></a><span class="lineno"> 48</span>  <span class="keyword">public</span>:</div><div class="line"><a name="l00049"></a><span class="lineno"> 49</span>  T& operator*(<span class="keywordtype">void</span>)</div><div class="line"><a name="l00050"></a><span class="lineno"> 50</span>  {</div><div class="line"><a name="l00051"></a><span class="lineno"> 51</span>  <span class="keywordflow">while</span> (!m_data)</div><div class="line"><a name="l00052"></a><span class="lineno"> 52</span>  {</div><div class="line"><a name="l00053"></a><span class="lineno"> 53</span>  <span class="keywordflow">if</span> (T *<span class="keyword">const</span> initializer = create())</div><div class="line"><a name="l00054"></a><span class="lineno"> 54</span>  {</div><div class="line"><a name="l00055"></a><span class="lineno"> 55</span>  <span class="keywordflow">if</span> (m_data.testAndSetOrdered(NULL, initializer))</div><div class="line"><a name="l00056"></a><span class="lineno"> 56</span>  {</div><div class="line"><a name="l00057"></a><span class="lineno"> 57</span>  <span class="keywordflow">return</span> *initializer;</div><div class="line"><a name="l00058"></a><span class="lineno"> 58</span>  }</div><div class="line"><a name="l00059"></a><span class="lineno"> 59</span>  }</div><div class="line"><a name="l00060"></a><span class="lineno"> 60</span>  <span class="keywordflow">else</span></div><div class="line"><a name="l00061"></a><span class="lineno"> 61</span>  {</div><div class="line"><a name="l00062"></a><span class="lineno"> 62</span>  MUTILS_THROW(<span class="stringliteral">"Initializer function returned NULL!"</span>);</div><div class="line"><a name="l00063"></a><span class="lineno"> 63</span>  }</div><div class="line"><a name="l00064"></a><span class="lineno"> 64</span>  }</div><div class="line"><a name="l00065"></a><span class="lineno"> 65</span>  <span class="keywordflow">return</span> *m_data;</div><div class="line"><a name="l00066"></a><span class="lineno"> 66</span>  }</div><div class="line"><a name="l00067"></a><span class="lineno"> 67</span> </div><div class="line"><a name="l00068"></a><span class="lineno"> 68</span>  <span class="keyword">protected</span>:</div><div class="line"><a name="l00069"></a><span class="lineno"> 69</span>  <span class="keyword">virtual</span> T *create() = 0;</div><div class="line"><a name="l00070"></a><span class="lineno"> 70</span> </div><div class="line"><a name="l00071"></a><span class="lineno"> 71</span>  <span class="keyword">private</span>:</div><div class="line"><a name="l00072"></a><span class="lineno"> 72</span>  QAtomicPointer<T> m_data;</div><div class="line"><a name="l00073"></a><span class="lineno"> 73</span>  };</div><div class="line"><a name="l00074"></a><span class="lineno"> 74</span> }</div><div class="ttc" id="_global_8h_html"><div class="ttname"><a href="../../d5/d3b/_global_8h.html">Global.h</a></div><div class="ttdoc">This file contains miscellaneous functions that are generally useful for Qt-based applications...</div></div>
-<div class="ttc" id="class_m_utils_1_1_lazy_html"><div class="ttname"><a href="../../d0/dce/class_m_utils_1_1_lazy.html">MUtils::Lazy</a></div><div class="ttdoc">Lazy initialization template class. </div><div class="ttdef"><b>Definition:</b> Lazy.h:46</div></div>
+<a href="../../d8/d4d/_lazy_8h.html">Go to the documentation of this file.</a><div class="fragment"><div class="line"><a name="l00001"></a><span class="lineno"> 1</span> <span class="comment">// MuldeR's Utilities for Qt</span></div><div class="line"><a name="l00003"></a><span class="lineno"> 3</span> <span class="comment">// Copyright (C) 2004-2017 LoRd_MuldeR <MuldeR2@GMX.de></span></div><div class="line"><a name="l00004"></a><span class="lineno"> 4</span> <span class="comment">//</span></div><div class="line"><a name="l00005"></a><span class="lineno"> 5</span> <span class="comment">// This library is free software; you can redistribute it and/or</span></div><div class="line"><a name="l00006"></a><span class="lineno"> 6</span> <span class="comment">// modify it under the terms of the GNU Lesser General Public</span></div><div class="line"><a name="l00007"></a><span class="lineno"> 7</span> <span class="comment">// License as published by the Free Software Foundation; either</span></div><div class="line"><a name="l00008"></a><span class="lineno"> 8</span> <span class="comment">// version 2.1 of the License, or (at your option) any later version.</span></div><div class="line"><a name="l00009"></a><span class="lineno"> 9</span> <span class="comment">//</span></div><div class="line"><a name="l00010"></a><span class="lineno"> 10</span> <span class="comment">// This library is distributed in the hope that it will be useful,</span></div><div class="line"><a name="l00011"></a><span class="lineno"> 11</span> <span class="comment">// but WITHOUT ANY WARRANTY; without even the implied warranty of</span></div><div class="line"><a name="l00012"></a><span class="lineno"> 12</span> <span class="comment">// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU</span></div><div class="line"><a name="l00013"></a><span class="lineno"> 13</span> <span class="comment">// Lesser General Public License for more details.</span></div><div class="line"><a name="l00014"></a><span class="lineno"> 14</span> <span class="comment">//</span></div><div class="line"><a name="l00015"></a><span class="lineno"> 15</span> <span class="comment">// You should have received a copy of the GNU Lesser General Public</span></div><div class="line"><a name="l00016"></a><span class="lineno"> 16</span> <span class="comment">// License along with this library; if not, write to the Free Software</span></div><div class="line"><a name="l00017"></a><span class="lineno"> 17</span> <span class="comment">// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA</span></div><div class="line"><a name="l00018"></a><span class="lineno"> 18</span> <span class="comment">//</span></div><div class="line"><a name="l00019"></a><span class="lineno"> 19</span> <span class="comment">// http://www.gnu.org/licenses/lgpl-2.1.txt</span></div><div class="line"><a name="l00021"></a><span class="lineno"> 21</span> <span class="comment"></span></div><div class="line"><a name="l00027"></a><span class="lineno"> 27</span> <span class="preprocessor">#pragma once</span></div><div class="line"><a name="l00028"></a><span class="lineno"> 28</span> </div><div class="line"><a name="l00029"></a><span class="lineno"> 29</span> <span class="comment">//MUtils</span></div><div class="line"><a name="l00030"></a><span class="lineno"> 30</span> <span class="preprocessor">#include <<a class="code" href="../../d5/d3b/_global_8h.html">MUtils/Global.h</a>></span></div><div class="line"><a name="l00031"></a><span class="lineno"> 31</span> <span class="preprocessor">#include <MUtils/Exception.h></span></div><div class="line"><a name="l00032"></a><span class="lineno"> 32</span> </div><div class="line"><a name="l00033"></a><span class="lineno"> 33</span> <span class="comment">//Qt</span></div><div class="line"><a name="l00034"></a><span class="lineno"> 34</span> <span class="preprocessor">#include <Q
AtomicPointer></span></div><div class="line"><a name="l00035"></a><span class="lineno"> 35</span> </div><div class="line"><a name="l00036"></a><span class="lineno"> 36</span> <span class="comment">//CRT</span></div><div class="line"><a name="l00037"></a><span class="lineno"> 37</span> <span class="preprocessor">#include <functional></span></div><div class="line"><a name="l00038"></a><span class="lineno"> 38</span> </div><div class="line"><a name="l00039"></a><span class="lineno"> 39</span> <span class="keyword">namespace </span><a class="code" href="../../d3/da6/namespace_m_utils.html">MUtils</a></div><div class="line"><a name="l00040"></a><span class="lineno"> 40</span> {</div><div class="line"><a name="l00048"></a><span class="lineno"><a class="line" href="../../d0/dce/class_m_utils_1_1_lazy.html"> 48</a></span>  <span class="keyword">template</span><<span class="keyword">typename</span> T> <span class="keyword">class </span><a class="code" href="../../d0/dce/class_m_utils_1_1_lazy.html">Lazy</a></div><div class="line"><a name="l00049"></a><span class="lineno"> 49</span>  {</div><div class="line"><a name="l00050"></a><span class="lineno"> 50</span>  <span class="keyword">public</span>:</div><div class="line"><a name="l00051"></a><span class="lineno"> 51</span>  <a class="code" href="../../d0/dce/class_m_utils_1_1_lazy.html">Lazy</a>(std::function<T*(<span class="keywordtype">void</span>)> &&initializer) : m_initializer(initializer) { }</div><div class="line"><a name="l00052"></a><span class="lineno"> 52</span> </div><div class="line"><a name="l00053"></a><span class="lineno"> 53</span>  T& operator*(<span class="keywordtype">void</span>)</div><div class="line"><a name="l00054"></a><span class="lineno"> 54</span>  {</div><div class="line"><a name="l00055"></a><span class="lineno"> 55</span>  <span class="keywordflow">while</span> (!m_value)</div><div class="line"><a name="l00056"></a><span class="lineno"> 56</span>  {</div><div class="line"><a name="l00057"></a><span class="lineno"> 57</span>  <span class="keywordflow">if</span> (T *<span class="keyword">const</span> value = m_initializer())</div><div class="line"><a name="l00058"></a><span class="lineno"> 58</span>  {</div><div class="line"><a name="l00059"></a><span class="lineno"> 59</span>  <span class="keywordflow">if</span> (!m_value.testAndSetOrdered(NULL, value))</div><div class="line"><a name="l00060"></a><span class="lineno"> 60</span>  {</div><div class="line"><a name="l00061"></a><span class="lineno"> 61</span>  <span class="keyword">delete</span> value; <span class="comment">/*too late*/</span></div><div class="line"><a name="l00062"></a><span class="lineno"> 62</span>  }</div><div class="line"><a name="l00063"></a><span class="lineno"> 63</span>  }</div><div class="line"><a name="l00064"></a><span class="lineno"> 64</span>  <span class="keywordflow">else</span></div><div class="line"><a name="l00065"></a><span class="lineno"> 65</span>  {</div><div class="line"><a name="l00066"></a><span class="lineno"> 66</span>  MUTILS_THROW(<span class="stringliteral">"Initializer returned NULL!"</span>);</div><div class="line"><a name="l00067"></a><span class="lineno"> 67</span>  }</div><div class="line"><a name="l00068"></a><span class="lineno"> 68</span>  }</div><div class="line"><a name="l00069"></a><span class="lineno"> 69</span>  <span class="keywordflow">return</span> *m_value;</div><div class="line"><a name="l00070"></a><span class="lineno"> 70</span>  }</div><div class="line"><a name="l00071"></a><span class="lineno"> 71</span> </div><div class="line"><a name="l00072"></a><span class="lineno"> 72</span>  <span class="keyword">private</span>:</div><div class="line"><a name="l00073"></a><span class="lineno"> 73</span>  QAtomicPointer<T> m_value;</div><div class="line"><a name="l00074"></a><span class="lineno"> 74</span>  <span class="keyword">const</span> std::function<T*(void)> m_initializer;</div><div class="line"><a name="l00075"></a><span class="lineno"> 75</span>  };</div><div class="line"><a name="l00076"></a><span class="lineno"> 76</span> }</div><div class="ttc" id="_global_8h_html"><div class="ttname"><a href="../../d5/d3b/_global_8h.html">Global.h</a></div><div class="ttdoc">This file contains miscellaneous functions that are generally useful for Qt-based applications...</div></div>
+<div class="ttc" id="class_m_utils_1_1_lazy_html"><div class="ttname"><a href="../../d0/dce/class_m_utils_1_1_lazy.html">MUtils::Lazy</a></div><div class="ttdoc">Lazy initialization template class. </div><div class="ttdef"><b>Definition:</b> Lazy.h:48</div></div>
<div class="ttc" id="namespace_m_utils_html"><div class="ttname"><a href="../../d3/da6/namespace_m_utils.html">MUtils</a></div><div class="ttdoc">Global MUtils namespace. </div><div class="ttdef"><b>Definition:</b> CPUFeatures.h:37</div></div>
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<!-- start footer part -->
<p>This is the complete list of members for <a class="el" href="../../d0/dce/class_m_utils_1_1_lazy.html">MUtils::Lazy< T ></a>, including all inherited members.</p>
<table class="directory">
- <tr bgcolor="#f0f0f0" class="even"><td class="entry"><b>create</b>()=0 (defined in <a class="el" href="../../d0/dce/class_m_utils_1_1_lazy.html">MUtils::Lazy< T ></a>)</td><td class="entry"><a class="el" href="../../d0/dce/class_m_utils_1_1_lazy.html">MUtils::Lazy< T ></a></td><td class="entry"><span class="mlabel">protected</span><span class="mlabel">pure virtual</span></td></tr>
+ <tr bgcolor="#f0f0f0" class="even"><td class="entry"><b>Lazy</b>(std::function< T *(void)> &&initializer) (defined in <a class="el" href="../../d0/dce/class_m_utils_1_1_lazy.html">MUtils::Lazy< T ></a>)</td><td class="entry"><a class="el" href="../../d0/dce/class_m_utils_1_1_lazy.html">MUtils::Lazy< T ></a></td><td class="entry"><span class="mlabel">inline</span></td></tr>
<tr bgcolor="#f0f0f0"><td class="entry"><b>operator*</b>(void) (defined in <a class="el" href="../../d0/dce/class_m_utils_1_1_lazy.html">MUtils::Lazy< T ></a>)</td><td class="entry"><a class="el" href="../../d0/dce/class_m_utils_1_1_lazy.html">MUtils::Lazy< T ></a></td><td class="entry"><span class="mlabel">inline</span></td></tr>
</table></div><!-- contents -->
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#include <MUtils/Exception.h>
//Qt
-#include <QScopedPointer>
#include <QAtomicPointer>
+//CRT
+#include <functional>
+
namespace MUtils
{
/**
* \brief Lazy initialization template class
*
- * In order to create your own "lazy" initializer, inherit from the `Lazy<T>` class an implement the create() function. The lazy-initialized value can be obtained from a `Lazy<T>` instance by using the `operator*()`. Initialization of the value happens when the `operator*()` is called for the very first time, by invoking the concrete create() function. The return value of create() is then stored internally, so that any subsequent call to the `operator*()` immediately returns the previously created value.
+ * The lazy-initialized value of type T can be obtained from a `Lazy<T>` instance by using the `operator*()`. Initialization of the value happens when the `operator*()` is called for the very first time, by invoking the `initializer` lambda-function that was passed to the constructor. The return value of the `initializer` lambda-function is then stored internally, so that any subsequent call to the `operator*()` *immediately* returns the previously created value.
*
- * **Note on thread-saftey:** This class is thread-safe in the sense that all calls to `operator*()` on the same `Lazy<T>` instance, regardless from which thread, are guaranteed to return the exactly same value/object. Still, if the value has *not* been initialized yet **and** if multiple threads happen to call `operator*()` at the same time, then the concrete create() function *may* be invoked more than once (concurrently and by different threads). In that case, all but one return value of create() are discarded, and all threads eventually receive the same value/object.
+ * **Note on thread-saftey:** This class is thread-safe in the sense that all calls to `operator*()` on the same `Lazy<T>` instance, regardless from which thread, are guaranteed to return the exactly same value/object. Still, if the value has *not* been initialized yet **and** if multiple threads happen to call `operator*()` at the same time, then the `initializer` lambda-function *may* be invoked more than once (concurrently and by different threads). In that case, all but one return value of the `initializer` lambda-function are discarded, and all threads eventually obtain the same value/object.
*/
template<typename T> class Lazy
{
public:
+ Lazy(std::function<T*(void)> &&initializer) : m_initializer(initializer) { }
+
T& operator*(void)
{
- while (!m_data)
+ while (!m_value)
{
- if (T *const initializer = create())
+ if (T *const value = m_initializer())
{
- if (!m_data.testAndSetOrdered(NULL, initializer))
+ if (!m_value.testAndSetOrdered(NULL, value))
{
- delete initializer;
+ delete value; /*too late*/
}
}
else
{
- MUTILS_THROW("Initializer function returned NULL!");
+ MUTILS_THROW("Initializer returned NULL!");
}
}
- return *m_data;
+ return *m_value;
}
- protected:
- virtual T *create() = 0;
-
private:
- QAtomicPointer<T> m_data;
+ QAtomicPointer<T> m_value;
+ const std::function<T*(void)> m_initializer;
};
}
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