--- /dev/null
+// -*- C++ -*-
+
+// Copyright (C) 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library. This library is free
+// software; you can redistribute it and/or modify it under the terms
+// of the GNU General Public License as published by the Free Software
+// Foundation; either version 3, or (at your option) any later
+// version.
+
+// This library is distributed in the hope that it will be useful, but
+// WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+// General Public License for more details.
+
+// Under Section 7 of GPL version 3, you are granted additional
+// permissions described in the GCC Runtime Library Exception, version
+// 3.1, as published by the Free Software Foundation.
+
+// You should have received a copy of the GNU General Public License and
+// a copy of the GCC Runtime Library Exception along with this program;
+// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
+// <http://www.gnu.org/licenses/>.
+
+/** @file parallel/queue.h
+ * @brief Lock-free double-ended queue.
+ * This file is a GNU parallel extension to the Standard C++ Library.
+ */
+
+// Written by Johannes Singler.
+
+#ifndef _GLIBCXX_PARALLEL_QUEUE_H
+#define _GLIBCXX_PARALLEL_QUEUE_H 1
+
+#include <parallel/types.h>
+#include <parallel/base.h>
+#include <parallel/compatibility.h>
+
+/** @brief Decide whether to declare certain variable volatile in this file. */
+#define _GLIBCXX_VOLATILE volatile
+
+namespace __gnu_parallel
+{
+ /**@brief Double-ended queue of bounded size, allowing lock-free
+ * atomic access. push_front() and pop_front() must not be called
+ * concurrently to each other, while pop_back() can be called
+ * concurrently at all times.
+ * @c empty(), @c size(), and @c top() are intentionally not provided.
+ * Calling them would not make sense in a concurrent setting.
+ * @param _Tp Contained element type. */
+ template<typename _Tp>
+ class _RestrictedBoundedConcurrentQueue
+ {
+ private:
+ /** @brief Array of elements, seen as cyclic buffer. */
+ _Tp* _M_base;
+
+ /** @brief Maximal number of elements contained at the same time. */
+ _SequenceIndex _M_max_size;
+
+ /** @brief Cyclic __begin and __end pointers contained in one
+ atomically changeable value. */
+ _GLIBCXX_VOLATILE _CASable _M_borders;
+
+ public:
+ /** @brief Constructor. Not to be called concurrent, of course.
+ * @param __max_size Maximal number of elements to be contained. */
+ _RestrictedBoundedConcurrentQueue(_SequenceIndex __max_size)
+ {
+ _M_max_size = __max_size;
+ _M_base = new _Tp[__max_size];
+ _M_borders = __encode2(0, 0);
+#pragma omp flush
+ }
+
+ /** @brief Destructor. Not to be called concurrent, of course. */
+ ~_RestrictedBoundedConcurrentQueue()
+ { delete[] _M_base; }
+
+ /** @brief Pushes one element into the queue at the front end.
+ * Must not be called concurrently with pop_front(). */
+ void
+ push_front(const _Tp& __t)
+ {
+ _CASable __former_borders = _M_borders;
+ int __former_front, __former_back;
+ __decode2(__former_borders, __former_front, __former_back);
+ *(_M_base + __former_front % _M_max_size) = __t;
+#if _GLIBCXX_ASSERTIONS
+ // Otherwise: front - back > _M_max_size eventually.
+ _GLIBCXX_PARALLEL_ASSERT(((__former_front + 1) - __former_back)
+ <= _M_max_size);
+#endif
+ __fetch_and_add(&_M_borders, __encode2(1, 0));
+ }
+
+ /** @brief Pops one element from the queue at the front end.
+ * Must not be called concurrently with pop_front(). */
+ bool
+ pop_front(_Tp& __t)
+ {
+ int __former_front, __former_back;
+#pragma omp flush
+ __decode2(_M_borders, __former_front, __former_back);
+ while (__former_front > __former_back)
+ {
+ // Chance.
+ _CASable __former_borders = __encode2(__former_front,
+ __former_back);
+ _CASable __new_borders = __encode2(__former_front - 1,
+ __former_back);
+ if (__compare_and_swap(&_M_borders, __former_borders,
+ __new_borders))
+ {
+ __t = *(_M_base + (__former_front - 1) % _M_max_size);
+ return true;
+ }
+#pragma omp flush
+ __decode2(_M_borders, __former_front, __former_back);
+ }
+ return false;
+ }
+
+ /** @brief Pops one element from the queue at the front end.
+ * Must not be called concurrently with pop_front(). */
+ bool
+ pop_back(_Tp& __t) //queue behavior
+ {
+ int __former_front, __former_back;
+#pragma omp flush
+ __decode2(_M_borders, __former_front, __former_back);
+ while (__former_front > __former_back)
+ {
+ // Chance.
+ _CASable __former_borders = __encode2(__former_front,
+ __former_back);
+ _CASable __new_borders = __encode2(__former_front,
+ __former_back + 1);
+ if (__compare_and_swap(&_M_borders, __former_borders,
+ __new_borders))
+ {
+ __t = *(_M_base + __former_back % _M_max_size);
+ return true;
+ }
+#pragma omp flush
+ __decode2(_M_borders, __former_front, __former_back);
+ }
+ return false;
+ }
+ };
+} //namespace __gnu_parallel
+
+#undef _GLIBCXX_VOLATILE
+
+#endif /* _GLIBCXX_PARALLEL_QUEUE_H */
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