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<li class="navelem"><a class="el" href="dir_3c80010775d22af2067790ecc9cdcf9d.html">librf</a></li><li class="navelem"><a class="el" href="dir_54ae0e78d997f6903cdf0996223d047f.html">src</a></li> </ul>
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<div class="title">ring_queue_lockfree.h</div> </div>
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<div class="contents">
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<div class="fragment"><div class="line"><a name="l00001"></a><span class="lineno"> 1</span> <span class="preprocessor">#pragma once</span></div>
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<div class="line"><a name="l00002"></a><span class="lineno"> 2</span>  </div>
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<div class="line"><a name="l00003"></a><span class="lineno"> 3</span> <span class="keyword">namespace </span>resumef</div>
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<div class="line"><a name="l00004"></a><span class="lineno"> 4</span> {</div>
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<div class="line"><a name="l00005"></a><span class="lineno"> 5</span>  <span class="comment">//目前无法解决三个索引数值回绕导致的问题</span></div>
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<div class="line"><a name="l00006"></a><span class="lineno"> 6</span>  <span class="comment">//如果为了避免索引回绕的问题，索引采用uint64_t类型，</span></div>
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<div class="line"><a name="l00007"></a><span class="lineno"> 7</span>  <span class="comment">//则在与spinlock<T, false, uint32_t>版本的对比中速度反而慢了</span></div>
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<div class="line"><a name="l00008"></a><span class="lineno"> 8</span>  <span class="comment">//pop时无法使用move语义来获取数据。因为算法要求先获取值，且获取后有可能失败，从而重新获取其它值。</span></div>
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<div class="line"><a name="l00009"></a><span class="lineno"> 9</span>  <span class="keyword">template</span><<span class="keyword">class</span> _Ty, <span class="keyword">class</span> _Sty = u<span class="keywordtype">int</span>32_t></div>
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<div class="line"><a name="l00010"></a><span class="lineno"> 10</span>  <span class="keyword">struct </span>ring_queue_lockfree</div>
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<div class="line"><a name="l00011"></a><span class="lineno"> 11</span>  {</div>
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<div class="line"><a name="l00012"></a><span class="lineno"> 12</span>  <span class="keyword">using</span> value_type = _Ty;</div>
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<div class="line"><a name="l00013"></a><span class="lineno"> 13</span>  <span class="keyword">using</span> size_type = _Sty;</div>
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<div class="line"><a name="l00014"></a><span class="lineno"> 14</span>  <span class="keyword">public</span>:</div>
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<div class="line"><a name="l00015"></a><span class="lineno"> 15</span>  ring_queue_lockfree(<span class="keywordtype">size_t</span> sz);</div>
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<div class="line"><a name="l00016"></a><span class="lineno"> 16</span>  </div>
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<div class="line"><a name="l00017"></a><span class="lineno"> 17</span>  ring_queue_lockfree(<span class="keyword">const</span> ring_queue_lockfree&) = <span class="keyword">delete</span>;</div>
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<div class="line"><a name="l00018"></a><span class="lineno"> 18</span>  ring_queue_lockfree(ring_queue_lockfree&&) = <span class="keywordflow">default</span>;</div>
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<div class="line"><a name="l00019"></a><span class="lineno"> 19</span>  ring_queue_lockfree& operator =(<span class="keyword">const</span> ring_queue_lockfree&) = <span class="keyword">delete</span>;</div>
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<div class="line"><a name="l00020"></a><span class="lineno"> 20</span>  ring_queue_lockfree& operator =(ring_queue_lockfree&&) = <span class="keywordflow">default</span>;</div>
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<div class="line"><a name="l00021"></a><span class="lineno"> 21</span>  </div>
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<div class="line"><a name="l00022"></a><span class="lineno"> 22</span>  <span class="keyword">auto</span> size() const noexcept->size_type;</div>
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<div class="line"><a name="l00023"></a><span class="lineno"> 23</span>  auto capacity() const noexcept->size_type;</div>
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<div class="line"><a name="l00024"></a><span class="lineno"> 24</span>  <span class="keywordtype">bool</span> empty() const noexcept;</div>
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<div class="line"><a name="l00025"></a><span class="lineno"> 25</span>  <span class="keywordtype">bool</span> full() const noexcept;</div>
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<div class="line"><a name="l00026"></a><span class="lineno"> 26</span>  template<class U></div>
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<div class="line"><a name="l00027"></a><span class="lineno"> 27</span>  <span class="keywordtype">bool</span> try_push(U&& value) noexcept(std::is_nothrow_move_constructible_v<U>);</div>
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<div class="line"><a name="l00028"></a><span class="lineno"> 28</span>  <span class="keywordtype">bool</span> try_pop(value_type& value) noexcept(std::is_nothrow_move_constructible_v<value_type>);</div>
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<div class="line"><a name="l00029"></a><span class="lineno"> 29</span>  private:</div>
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<div class="line"><a name="l00030"></a><span class="lineno"> 30</span>  std::unique_ptr<value_type[]> m_bufferPtr;</div>
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<div class="line"><a name="l00031"></a><span class="lineno"> 31</span>  size_type m_bufferSize;</div>
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<div class="line"><a name="l00032"></a><span class="lineno"> 32</span>  </div>
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<div class="line"><a name="l00033"></a><span class="lineno"> 33</span>  std::atomic<size_type> m_writeIndex; <span class="comment">//Where a new element will be inserted to.</span></div>
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<div class="line"><a name="l00034"></a><span class="lineno"> 34</span>  std::atomic<size_type> m_readIndex; <span class="comment">//Where the next element where be extracted from.</span></div>
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<div class="line"><a name="l00035"></a><span class="lineno"> 35</span>  std::atomic<size_type> m_maximumReadIndex; <span class="comment">//It points to the place where the latest "commited" data has been inserted. </span></div>
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<div class="line"><a name="l00036"></a><span class="lineno"> 36</span>  <span class="comment">//If it's not the same as writeIndex it means there are writes pending to be "commited" to the queue, </span></div>
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<div class="line"><a name="l00037"></a><span class="lineno"> 37</span>  <span class="comment">//that means that the place for the data was reserved (the index in the array) </span></div>
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<div class="line"><a name="l00038"></a><span class="lineno"> 38</span>  <span class="comment">//but the data is still not in the queue, </span></div>
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<div class="line"><a name="l00039"></a><span class="lineno"> 39</span>  <span class="comment">//so the thread trying to read will have to wait for those other threads to </span></div>
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<div class="line"><a name="l00040"></a><span class="lineno"> 40</span>  <span class="comment">//save the data into the queue.</span></div>
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<div class="line"><a name="l00041"></a><span class="lineno"> 41</span>  <span class="preprocessor">#ifdef _WITH_LOCK_FREE_Q_KEEP_REAL_SIZE</span></div>
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<div class="line"><a name="l00042"></a><span class="lineno"> 42</span>  std::atomic<size_type> m_count;</div>
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<div class="line"><a name="l00043"></a><span class="lineno"> 43</span> <span class="preprocessor"> #endif</span></div>
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<div class="line"><a name="l00044"></a><span class="lineno"> 44</span>  </div>
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<div class="line"><a name="l00045"></a><span class="lineno"> 45</span>  <span class="keyword">auto</span> countToIndex(size_type a_count) <span class="keyword">const</span> noexcept->size_type;</div>
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<div class="line"><a name="l00046"></a><span class="lineno"> 46</span>  <span class="keyword">auto</span> nextIndex(size_type a_count) <span class="keyword">const</span> noexcept->size_type;</div>
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<div class="line"><a name="l00047"></a><span class="lineno"> 47</span>  };</div>
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<div class="line"><a name="l00048"></a><span class="lineno"> 48</span>  </div>
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<div class="line"><a name="l00049"></a><span class="lineno"> 49</span>  <span class="keyword">template</span><<span class="keyword">class</span> _Ty, <span class="keyword">class</span> _Sty></div>
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<div class="line"><a name="l00050"></a><span class="lineno"> 50</span>  ring_queue_lockfree<_Ty, _Sty>::ring_queue_lockfree(<span class="keywordtype">size_t</span> sz)</div>
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<div class="line"><a name="l00051"></a><span class="lineno"> 51</span>  : m_bufferPtr(new value_type[sz + 1])</div>
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<div class="line"><a name="l00052"></a><span class="lineno"> 52</span>  , m_bufferSize(static_cast<size_type>(sz + 1))</div>
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<div class="line"><a name="l00053"></a><span class="lineno"> 53</span>  , m_writeIndex(0)</div>
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<div class="line"><a name="l00054"></a><span class="lineno"> 54</span>  , m_readIndex(0)</div>
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<div class="line"><a name="l00055"></a><span class="lineno"> 55</span>  , m_maximumReadIndex(0)</div>
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<div class="line"><a name="l00056"></a><span class="lineno"> 56</span>  #ifdef _WITH_LOCK_FREE_Q_KEEP_REAL_SIZE</div>
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<div class="line"><a name="l00057"></a><span class="lineno"> 57</span>  , m_count(0)</div>
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<div class="line"><a name="l00058"></a><span class="lineno"> 58</span>  #endif</div>
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<div class="line"><a name="l00059"></a><span class="lineno"> 59</span>  {</div>
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<div class="line"><a name="l00060"></a><span class="lineno"> 60</span>  assert(sz < (std::numeric_limits<size_type>::max)());</div>
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<div class="line"><a name="l00061"></a><span class="lineno"> 61</span>  }</div>
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||
<div class="line"><a name="l00062"></a><span class="lineno"> 62</span>  </div>
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<div class="line"><a name="l00063"></a><span class="lineno"> 63</span>  <span class="keyword">template</span><<span class="keyword">class</span> _Ty, <span class="keyword">class</span> _Sty></div>
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<div class="line"><a name="l00064"></a><span class="lineno"> 64</span>  <span class="keyword">auto</span> ring_queue_lockfree<_Ty, _Sty>::countToIndex(size_type a_count) <span class="keyword">const</span> noexcept->size_type</div>
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<div class="line"><a name="l00065"></a><span class="lineno"> 65</span>  {</div>
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<div class="line"><a name="l00066"></a><span class="lineno"> 66</span>  <span class="comment">//return (a_count % m_bufferSize);</span></div>
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<div class="line"><a name="l00067"></a><span class="lineno"> 67</span>  <span class="keywordflow">return</span> a_count;</div>
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<div class="line"><a name="l00068"></a><span class="lineno"> 68</span>  }</div>
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<div class="line"><a name="l00069"></a><span class="lineno"> 69</span>  </div>
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<div class="line"><a name="l00070"></a><span class="lineno"> 70</span>  <span class="keyword">template</span><<span class="keyword">class</span> _Ty, <span class="keyword">class</span> _Sty></div>
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<div class="line"><a name="l00071"></a><span class="lineno"> 71</span>  <span class="keyword">auto</span> ring_queue_lockfree<_Ty, _Sty>::nextIndex(size_type a_count) <span class="keyword">const</span> noexcept->size_type</div>
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<div class="line"><a name="l00072"></a><span class="lineno"> 72</span>  {</div>
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<div class="line"><a name="l00073"></a><span class="lineno"> 73</span>  <span class="comment">//return static_cast<size_type>((a_count + 1));</span></div>
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<div class="line"><a name="l00074"></a><span class="lineno"> 74</span>  <span class="keywordflow">return</span> <span class="keyword">static_cast<</span>size_type<span class="keyword">></span>((a_count + 1) % m_bufferSize);</div>
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<div class="line"><a name="l00075"></a><span class="lineno"> 75</span>  }</div>
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<div class="line"><a name="l00076"></a><span class="lineno"> 76</span>  </div>
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<div class="line"><a name="l00077"></a><span class="lineno"> 77</span>  <span class="keyword">template</span><<span class="keyword">class</span> _Ty, <span class="keyword">class</span> _Sty></div>
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<div class="line"><a name="l00078"></a><span class="lineno"> 78</span>  <span class="keyword">auto</span> ring_queue_lockfree<_Ty, _Sty>::size() const noexcept->size_type</div>
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<div class="line"><a name="l00079"></a><span class="lineno"> 79</span>  {</div>
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<div class="line"><a name="l00080"></a><span class="lineno"> 80</span> <span class="preprocessor"> #ifdef _WITH_LOCK_FREE_Q_KEEP_REAL_SIZE</span></div>
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<div class="line"><a name="l00081"></a><span class="lineno"> 81</span>  <span class="keywordflow">return</span> m_count.load();</div>
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<div class="line"><a name="l00082"></a><span class="lineno"> 82</span> <span class="preprocessor"> #else</span></div>
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<div class="line"><a name="l00083"></a><span class="lineno"> 83</span>  <span class="keyword">auto</span> currentWriteIndex = m_maximumReadIndex.load(std::memory_order_acquire);</div>
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<div class="line"><a name="l00084"></a><span class="lineno"> 84</span>  currentWriteIndex = countToIndex(currentWriteIndex);</div>
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<div class="line"><a name="l00085"></a><span class="lineno"> 85</span>  </div>
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<div class="line"><a name="l00086"></a><span class="lineno"> 86</span>  <span class="keyword">auto</span> currentReadIndex = m_readIndex.load(std::memory_order_acquire);</div>
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<div class="line"><a name="l00087"></a><span class="lineno"> 87</span>  currentReadIndex = countToIndex(currentReadIndex);</div>
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<div class="line"><a name="l00088"></a><span class="lineno"> 88</span>  </div>
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<div class="line"><a name="l00089"></a><span class="lineno"> 89</span>  <span class="keywordflow">if</span> (currentWriteIndex >= currentReadIndex)</div>
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<div class="line"><a name="l00090"></a><span class="lineno"> 90</span>  <span class="keywordflow">return</span> (currentWriteIndex - currentReadIndex);</div>
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<div class="line"><a name="l00091"></a><span class="lineno"> 91</span>  <span class="keywordflow">else</span></div>
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||
<div class="line"><a name="l00092"></a><span class="lineno"> 92</span>  <span class="keywordflow">return</span> (m_bufferSize + currentWriteIndex - currentReadIndex);</div>
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<div class="line"><a name="l00093"></a><span class="lineno"> 93</span> <span class="preprocessor"> #endif // _WITH_LOCK_FREE_Q_KEEP_REAL_SIZE</span></div>
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<div class="line"><a name="l00094"></a><span class="lineno"> 94</span>  }</div>
|
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<div class="line"><a name="l00095"></a><span class="lineno"> 95</span>  </div>
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<div class="line"><a name="l00096"></a><span class="lineno"> 96</span>  <span class="keyword">template</span><<span class="keyword">class</span> _Ty, <span class="keyword">class</span> _Sty></div>
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<div class="line"><a name="l00097"></a><span class="lineno"> 97</span>  <span class="keyword">auto</span> ring_queue_lockfree<_Ty, _Sty>::capacity() const noexcept->size_type</div>
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<div class="line"><a name="l00098"></a><span class="lineno"> 98</span>  {</div>
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<div class="line"><a name="l00099"></a><span class="lineno"> 99</span>  <span class="keywordflow">return</span> m_bufferSize - 1;</div>
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<div class="line"><a name="l00100"></a><span class="lineno"> 100</span>  }</div>
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<div class="line"><a name="l00101"></a><span class="lineno"> 101</span>  </div>
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<div class="line"><a name="l00102"></a><span class="lineno"> 102</span>  <span class="keyword">template</span><<span class="keyword">class</span> _Ty, <span class="keyword">class</span> _Sty></div>
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<div class="line"><a name="l00103"></a><span class="lineno"> 103</span>  <span class="keywordtype">bool</span> ring_queue_lockfree<_Ty, _Sty>::empty() const noexcept</div>
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<div class="line"><a name="l00104"></a><span class="lineno"> 104</span>  {</div>
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<div class="line"><a name="l00105"></a><span class="lineno"> 105</span> <span class="preprocessor"> #ifdef _WITH_LOCK_FREE_Q_KEEP_REAL_SIZE</span></div>
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<div class="line"><a name="l00106"></a><span class="lineno"> 106</span>  <span class="keywordflow">return</span> m_count.load() == 0;</div>
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<div class="line"><a name="l00107"></a><span class="lineno"> 107</span> <span class="preprocessor"> #else</span></div>
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<div class="line"><a name="l00108"></a><span class="lineno"> 108</span>  <span class="keyword">auto</span> currentWriteIndex = m_maximumReadIndex.load(std::memory_order_acquire);</div>
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<div class="line"><a name="l00109"></a><span class="lineno"> 109</span>  <span class="keyword">auto</span> currentReadIndex = m_readIndex.load(std::memory_order_acquire);</div>
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<div class="line"><a name="l00110"></a><span class="lineno"> 110</span>  <span class="keywordflow">return</span> countToIndex(currentWriteIndex) == countToIndex(currentReadIndex);</div>
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<div class="line"><a name="l00111"></a><span class="lineno"> 111</span> <span class="preprocessor"> #endif // _WITH_LOCK_FREE_Q_KEEP_REAL_SIZE</span></div>
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<div class="line"><a name="l00112"></a><span class="lineno"> 112</span>  }</div>
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<div class="line"><a name="l00113"></a><span class="lineno"> 113</span>  </div>
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<div class="line"><a name="l00114"></a><span class="lineno"> 114</span>  <span class="keyword">template</span><<span class="keyword">class</span> _Ty, <span class="keyword">class</span> _Sty></div>
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<div class="line"><a name="l00115"></a><span class="lineno"> 115</span>  <span class="keywordtype">bool</span> ring_queue_lockfree<_Ty, _Sty>::full() const noexcept</div>
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<div class="line"><a name="l00116"></a><span class="lineno"> 116</span>  {</div>
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<div class="line"><a name="l00117"></a><span class="lineno"> 117</span> <span class="preprocessor"> #ifdef _WITH_LOCK_FREE_Q_KEEP_REAL_SIZE</span></div>
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<div class="line"><a name="l00118"></a><span class="lineno"> 118</span>  <span class="keywordflow">return</span> (m_count.load() == (m_bufferSize - 1));</div>
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<div class="line"><a name="l00119"></a><span class="lineno"> 119</span> <span class="preprocessor"> #else</span></div>
|
||
<div class="line"><a name="l00120"></a><span class="lineno"> 120</span>  <span class="keyword">auto</span> currentWriteIndex = m_writeIndex.load(std::memory_order_acquire);</div>
|
||
<div class="line"><a name="l00121"></a><span class="lineno"> 121</span>  <span class="keyword">auto</span> currentReadIndex = m_readIndex.load(std::memory_order_acquire);</div>
|
||
<div class="line"><a name="l00122"></a><span class="lineno"> 122</span>  <span class="keywordflow">return</span> countToIndex(nextIndex(currentWriteIndex)) == countToIndex(currentReadIndex);</div>
|
||
<div class="line"><a name="l00123"></a><span class="lineno"> 123</span> <span class="preprocessor"> #endif // _WITH_LOCK_FREE_Q_KEEP_REAL_SIZE</span></div>
|
||
<div class="line"><a name="l00124"></a><span class="lineno"> 124</span>  }</div>
|
||
<div class="line"><a name="l00125"></a><span class="lineno"> 125</span>  </div>
|
||
<div class="line"><a name="l00126"></a><span class="lineno"> 126</span>  <span class="keyword">template</span><<span class="keyword">class</span> _Ty, <span class="keyword">class</span> _Sty></div>
|
||
<div class="line"><a name="l00127"></a><span class="lineno"> 127</span>  <span class="keyword">template</span><<span class="keyword">class</span> U></div>
|
||
<div class="line"><a name="l00128"></a><span class="lineno"> 128</span>  <span class="keywordtype">bool</span> ring_queue_lockfree<_Ty, _Sty>::try_push(U&& value) noexcept(std::is_nothrow_move_constructible_v<U>)</div>
|
||
<div class="line"><a name="l00129"></a><span class="lineno"> 129</span>  {</div>
|
||
<div class="line"><a name="l00130"></a><span class="lineno"> 130</span>  <span class="keyword">auto</span> currentWriteIndex = m_writeIndex.load(std::memory_order_acquire);</div>
|
||
<div class="line"><a name="l00131"></a><span class="lineno"> 131</span>  </div>
|
||
<div class="line"><a name="l00132"></a><span class="lineno"> 132</span>  <span class="keywordflow">do</span></div>
|
||
<div class="line"><a name="l00133"></a><span class="lineno"> 133</span>  {</div>
|
||
<div class="line"><a name="l00134"></a><span class="lineno"> 134</span>  <span class="keywordflow">if</span> (countToIndex(nextIndex(currentWriteIndex)) == countToIndex(m_readIndex.load(std::memory_order_acquire)))</div>
|
||
<div class="line"><a name="l00135"></a><span class="lineno"> 135</span>  {</div>
|
||
<div class="line"><a name="l00136"></a><span class="lineno"> 136</span>  <span class="comment">// the queue is full</span></div>
|
||
<div class="line"><a name="l00137"></a><span class="lineno"> 137</span>  <span class="keywordflow">return</span> <span class="keyword">false</span>;</div>
|
||
<div class="line"><a name="l00138"></a><span class="lineno"> 138</span>  }</div>
|
||
<div class="line"><a name="l00139"></a><span class="lineno"> 139</span>  </div>
|
||
<div class="line"><a name="l00140"></a><span class="lineno"> 140</span>  <span class="comment">// There is more than one producer. Keep looping till this thread is able </span></div>
|
||
<div class="line"><a name="l00141"></a><span class="lineno"> 141</span>  <span class="comment">// to allocate space for current piece of data</span></div>
|
||
<div class="line"><a name="l00142"></a><span class="lineno"> 142</span>  <span class="comment">//</span></div>
|
||
<div class="line"><a name="l00143"></a><span class="lineno"> 143</span>  <span class="comment">// using compare_exchange_strong because it isn't allowed to fail spuriously</span></div>
|
||
<div class="line"><a name="l00144"></a><span class="lineno"> 144</span>  <span class="comment">// When the compare_exchange operation is in a loop the weak version</span></div>
|
||
<div class="line"><a name="l00145"></a><span class="lineno"> 145</span>  <span class="comment">// will yield better performance on some platforms, but here we'd have to</span></div>
|
||
<div class="line"><a name="l00146"></a><span class="lineno"> 146</span>  <span class="comment">// load m_writeIndex all over again</span></div>
|
||
<div class="line"><a name="l00147"></a><span class="lineno"> 147</span>  } <span class="keywordflow">while</span> (!m_writeIndex.compare_exchange_strong(currentWriteIndex, nextIndex(currentWriteIndex), std::memory_order_acq_rel));</div>
|
||
<div class="line"><a name="l00148"></a><span class="lineno"> 148</span>  </div>
|
||
<div class="line"><a name="l00149"></a><span class="lineno"> 149</span>  <span class="comment">// Just made sure this index is reserved for this thread.</span></div>
|
||
<div class="line"><a name="l00150"></a><span class="lineno"> 150</span>  m_bufferPtr[countToIndex(currentWriteIndex)] = std::move(value);</div>
|
||
<div class="line"><a name="l00151"></a><span class="lineno"> 151</span>  </div>
|
||
<div class="line"><a name="l00152"></a><span class="lineno"> 152</span>  <span class="comment">// update the maximum read index after saving the piece of data. It can't</span></div>
|
||
<div class="line"><a name="l00153"></a><span class="lineno"> 153</span>  <span class="comment">// fail if there is only one thread inserting in the queue. It might fail </span></div>
|
||
<div class="line"><a name="l00154"></a><span class="lineno"> 154</span>  <span class="comment">// if there is more than 1 producer thread because this operation has to</span></div>
|
||
<div class="line"><a name="l00155"></a><span class="lineno"> 155</span>  <span class="comment">// be done in the same order as the previous CAS</span></div>
|
||
<div class="line"><a name="l00156"></a><span class="lineno"> 156</span>  <span class="comment">//</span></div>
|
||
<div class="line"><a name="l00157"></a><span class="lineno"> 157</span>  <span class="comment">// using compare_exchange_weak because they are allowed to fail spuriously</span></div>
|
||
<div class="line"><a name="l00158"></a><span class="lineno"> 158</span>  <span class="comment">// (act as if *this != expected, even if they are equal), but when the</span></div>
|
||
<div class="line"><a name="l00159"></a><span class="lineno"> 159</span>  <span class="comment">// compare_exchange operation is in a loop the weak version will yield</span></div>
|
||
<div class="line"><a name="l00160"></a><span class="lineno"> 160</span>  <span class="comment">// better performance on some platforms.</span></div>
|
||
<div class="line"><a name="l00161"></a><span class="lineno"> 161</span>  <span class="keyword">auto</span> savedWriteIndex = currentWriteIndex;</div>
|
||
<div class="line"><a name="l00162"></a><span class="lineno"> 162</span>  <span class="keywordflow">while</span> (!m_maximumReadIndex.compare_exchange_weak(currentWriteIndex, nextIndex(currentWriteIndex), std::memory_order_acq_rel))</div>
|
||
<div class="line"><a name="l00163"></a><span class="lineno"> 163</span>  {</div>
|
||
<div class="line"><a name="l00164"></a><span class="lineno"> 164</span>  currentWriteIndex = savedWriteIndex;</div>
|
||
<div class="line"><a name="l00165"></a><span class="lineno"> 165</span>  <span class="comment">// this is a good place to yield the thread in case there are more</span></div>
|
||
<div class="line"><a name="l00166"></a><span class="lineno"> 166</span>  <span class="comment">// software threads than hardware processors and you have more</span></div>
|
||
<div class="line"><a name="l00167"></a><span class="lineno"> 167</span>  <span class="comment">// than 1 producer thread</span></div>
|
||
<div class="line"><a name="l00168"></a><span class="lineno"> 168</span>  <span class="comment">// have a look at sched_yield (POSIX.1b)</span></div>
|
||
<div class="line"><a name="l00169"></a><span class="lineno"> 169</span>  std::this_thread::yield();</div>
|
||
<div class="line"><a name="l00170"></a><span class="lineno"> 170</span>  }</div>
|
||
<div class="line"><a name="l00171"></a><span class="lineno"> 171</span>  </div>
|
||
<div class="line"><a name="l00172"></a><span class="lineno"> 172</span>  <span class="comment">// The value was successfully inserted into the queue</span></div>
|
||
<div class="line"><a name="l00173"></a><span class="lineno"> 173</span> <span class="preprocessor"> #ifdef _WITH_LOCK_FREE_Q_KEEP_REAL_SIZE</span></div>
|
||
<div class="line"><a name="l00174"></a><span class="lineno"> 174</span>  m_count.fetch_add(1);</div>
|
||
<div class="line"><a name="l00175"></a><span class="lineno"> 175</span> <span class="preprocessor"> #endif</span></div>
|
||
<div class="line"><a name="l00176"></a><span class="lineno"> 176</span>  <span class="keywordflow">return</span> <span class="keyword">true</span>;</div>
|
||
<div class="line"><a name="l00177"></a><span class="lineno"> 177</span>  }</div>
|
||
<div class="line"><a name="l00178"></a><span class="lineno"> 178</span>  </div>
|
||
<div class="line"><a name="l00179"></a><span class="lineno"> 179</span>  <span class="keyword">template</span><<span class="keyword">class</span> _Ty, <span class="keyword">class</span> _Sty></div>
|
||
<div class="line"><a name="l00180"></a><span class="lineno"> 180</span>  <span class="keywordtype">bool</span> ring_queue_lockfree<_Ty, _Sty>::try_pop(value_type& value) noexcept(std::is_nothrow_move_constructible_v<value_type>)</div>
|
||
<div class="line"><a name="l00181"></a><span class="lineno"> 181</span>  {</div>
|
||
<div class="line"><a name="l00182"></a><span class="lineno"> 182</span>  <span class="keyword">auto</span> currentReadIndex = m_readIndex.load(std::memory_order_acquire);</div>
|
||
<div class="line"><a name="l00183"></a><span class="lineno"> 183</span>  </div>
|
||
<div class="line"><a name="l00184"></a><span class="lineno"> 184</span>  <span class="keywordflow">for</span> (;;)</div>
|
||
<div class="line"><a name="l00185"></a><span class="lineno"> 185</span>  {</div>
|
||
<div class="line"><a name="l00186"></a><span class="lineno"> 186</span>  <span class="keyword">auto</span> idx = countToIndex(currentReadIndex);</div>
|
||
<div class="line"><a name="l00187"></a><span class="lineno"> 187</span>  </div>
|
||
<div class="line"><a name="l00188"></a><span class="lineno"> 188</span>  <span class="comment">// to ensure thread-safety when there is more than 1 producer </span></div>
|
||
<div class="line"><a name="l00189"></a><span class="lineno"> 189</span>  <span class="comment">// thread a second index is defined (m_maximumReadIndex)</span></div>
|
||
<div class="line"><a name="l00190"></a><span class="lineno"> 190</span>  <span class="keywordflow">if</span> (idx == countToIndex(m_maximumReadIndex.load(std::memory_order_acquire)))</div>
|
||
<div class="line"><a name="l00191"></a><span class="lineno"> 191</span>  {</div>
|
||
<div class="line"><a name="l00192"></a><span class="lineno"> 192</span>  <span class="comment">// the queue is empty or</span></div>
|
||
<div class="line"><a name="l00193"></a><span class="lineno"> 193</span>  <span class="comment">// a producer thread has allocate space in the queue but is </span></div>
|
||
<div class="line"><a name="l00194"></a><span class="lineno"> 194</span>  <span class="comment">// waiting to commit the data into it</span></div>
|
||
<div class="line"><a name="l00195"></a><span class="lineno"> 195</span>  <span class="keywordflow">return</span> <span class="keyword">false</span>;</div>
|
||
<div class="line"><a name="l00196"></a><span class="lineno"> 196</span>  }</div>
|
||
<div class="line"><a name="l00197"></a><span class="lineno"> 197</span>  </div>
|
||
<div class="line"><a name="l00198"></a><span class="lineno"> 198</span>  <span class="comment">// retrieve the data from the queue</span></div>
|
||
<div class="line"><a name="l00199"></a><span class="lineno"> 199</span>  value = m_bufferPtr[idx]; <span class="comment">//但是，这里的方法不适合。如果只支持移动怎么办？</span></div>
|
||
<div class="line"><a name="l00200"></a><span class="lineno"> 200</span>  </div>
|
||
<div class="line"><a name="l00201"></a><span class="lineno"> 201</span>  <span class="comment">// try to perfrom now the CAS operation on the read index. If we succeed</span></div>
|
||
<div class="line"><a name="l00202"></a><span class="lineno"> 202</span>  <span class="comment">// a_data already contains what m_readIndex pointed to before we </span></div>
|
||
<div class="line"><a name="l00203"></a><span class="lineno"> 203</span>  <span class="comment">// increased it</span></div>
|
||
<div class="line"><a name="l00204"></a><span class="lineno"> 204</span>  <span class="keywordflow">if</span> (m_readIndex.compare_exchange_strong(currentReadIndex, nextIndex(currentReadIndex), std::memory_order_acq_rel))</div>
|
||
<div class="line"><a name="l00205"></a><span class="lineno"> 205</span>  {</div>
|
||
<div class="line"><a name="l00206"></a><span class="lineno"> 206</span>  <span class="comment">// got here. The value was retrieved from the queue. Note that the</span></div>
|
||
<div class="line"><a name="l00207"></a><span class="lineno"> 207</span>  <span class="comment">// data inside the m_queue array is not deleted nor reseted</span></div>
|
||
<div class="line"><a name="l00208"></a><span class="lineno"> 208</span> <span class="preprocessor"> #ifdef _WITH_LOCK_FREE_Q_KEEP_REAL_SIZE</span></div>
|
||
<div class="line"><a name="l00209"></a><span class="lineno"> 209</span>  m_count.fetch_sub(1);</div>
|
||
<div class="line"><a name="l00210"></a><span class="lineno"> 210</span> <span class="preprocessor"> #endif</span></div>
|
||
<div class="line"><a name="l00211"></a><span class="lineno"> 211</span>  <span class="keywordflow">return</span> <span class="keyword">true</span>;</div>
|
||
<div class="line"><a name="l00212"></a><span class="lineno"> 212</span>  }</div>
|
||
<div class="line"><a name="l00213"></a><span class="lineno"> 213</span>  </div>
|
||
<div class="line"><a name="l00214"></a><span class="lineno"> 214</span>  <span class="comment">// it failed retrieving the element off the queue. Someone else must</span></div>
|
||
<div class="line"><a name="l00215"></a><span class="lineno"> 215</span>  <span class="comment">// have read the element stored at countToIndex(currentReadIndex)</span></div>
|
||
<div class="line"><a name="l00216"></a><span class="lineno"> 216</span>  <span class="comment">// before we could perform the CAS operation </span></div>
|
||
<div class="line"><a name="l00217"></a><span class="lineno"> 217</span>  } <span class="comment">// keep looping to try again!</span></div>
|
||
<div class="line"><a name="l00218"></a><span class="lineno"> 218</span>  }</div>
|
||
<div class="line"><a name="l00219"></a><span class="lineno"> 219</span> }</div>
|
||
</div><!-- fragment --></div><!-- contents -->
|
||
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|
||
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|
||
制作者  <a href="http://www.doxygen.org/index.html">
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|
||
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