Start of work on lockfreee async queue

include/spdlog/details/mpcs_q.h

+#pragma once
+/*************************************************************************/
+/*
+Modified version of Intrusive MPSC node-based queue
+
+Original code from
+http://www.1024cores.net/home/lock-free-algorithms/queues/intrusive-mpsc-node-based-queue
+licensed by Dmitry Vyukov under the terms below:
+
+Simplified BSD license
+
+Copyright (c) 2010-2011 Dmitry Vyukov. All rights reserved.
+Redistribution and use in source and binary forms, with or without modification,
+are permitted provided that the following conditions are met:
+1. Redistributions of source code must retain the above copyright notice, this list of
+conditions and the following disclaimer.
+
+2. Redistributions in binary form must reproduce the above copyright notice, this list
+of conditions and the following disclaimer in the documentation and/or other materials
+provided with the distribution.
+
+THIS SOFTWARE IS PROVIDED BY DMITRY VYUKOV "AS IS" AND ANY EXPRESS OR IMPLIED
+WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
+SHALL DMITRY VYUKOV OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
+OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
+OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
+ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+The views and conclusions contained in the software and documentation are those of the authors and
+should not be interpreted as representing official policies, either expressed or implied, of Dmitry Vyukov.
+
+/*************************************************************************/
+/* The code in its current form adds the license below:                  */
+/*************************************************************************/
+/* spdlog - an extremely fast and easy to use c++11 logging library.     */
+/* Copyright (c) 2014 Gabi Melman.                                       */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+
+#include <atomic>
+namespace spdlog {
+namespace details {
+template<typename T>
+class mpsc_q
+{
+
+public:
+    mpsc_q(size_t size) :_stub(T()), _head(&_stub), _tail(&_stub)
+    {
+        _stub.next = nullptr;
+    }
+
+    ~mpsc_q()
+    {
+        reset();
+    }
+
+    void reset()
+    {
+        T dummy_val;
+        while (pop(dummy_val));
+    }
+
+    bool push(const T& value)
+    {
+        mpscq_node_t* new_node = new mpscq_node_t(value);
+        push_node(new_node);
+        return true;
+    }
+
+    bool pop(T& value)
+    {
+        mpscq_node_t* node = pop_node();
+        if (node != nullptr)
+        {
+            value = node->value;
+            delete(node);
+            return true;
+        }
+        else
+        {
+            return false;
+        }
+    }
+
+private:
+    struct mpscq_node_t
+    {
+        std::atomic<mpscq_node_t*>  next;
+        T value;
+
+        explicit mpscq_node_t(const T& value) :next(nullptr), value(value)
+        {
+        }
+    };
+
+    mpscq_node_t            _stub;
+    std::atomic<mpscq_node_t*>  _head;
+    mpscq_node_t*           _tail;
+
+
+
+    void push_node(mpscq_node_t* n)
+    {
+        n->next = nullptr;
+        mpscq_node_t* prev = _head.exchange(n);
+        prev->next = n;
+    }
+
+    mpscq_node_t* pop_node()
+    {
+        mpscq_node_t* tail = _tail;
+        mpscq_node_t* next = tail->next;
+        if (tail == &_stub)
+        {
+            if (nullptr == next)
+                return nullptr;
+            _tail = next;
+            tail = next;
+            next = next->next;
+        }
+        if (next)
+        {
+            _tail = next;
+            return tail;
+        }
+        mpscq_node_t* head = _head;
+        if (tail != head)
+            return 0;
+
+        push_node(&_stub);
+        next = tail->next;
+        if (next)
+        {
+            _tail = next;
+            return tail;
+        }
+        return nullptr;
+    }
+
+
+
+};
+}
+}
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