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// -*- C++ -*-
// Copyright (C) 2007, 2008, 2009 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 T Contained element type. */
template<typename T>
class RestrictedBoundedConcurrentQueue
{
private:
/** @brief Array of elements, seen as cyclic buffer. */
T* base;
/** @brief Maximal number of elements contained at the same time. */
sequence_index_t max_size;
/** @brief Cyclic begin and end pointers contained in one
atomically changeable value. */
_GLIBCXX_VOLATILE lcas_t borders;
public:
/** @brief Constructor. Not to be called concurrent, of course.
* @param max_size Maximal number of elements to be contained. */
RestrictedBoundedConcurrentQueue(sequence_index_t max_size)
{
this->max_size = max_size;
base = new T[max_size];
borders = encode2(0, 0);
#pragma omp flush
}
/** @brief Destructor. Not to be called concurrent, of course. */
~RestrictedBoundedConcurrentQueue()
{ delete[] base; }
/** @brief Pushes one element into the queue at the front end.
* Must not be called concurrently with pop_front(). */
void
push_front(const T& t)
{
lcas_t former_borders = borders;
int former_front, former_back;
decode2(former_borders, former_front, former_back);
*(base + former_front % max_size) = t;
#if _GLIBCXX_ASSERTIONS
// Otherwise: front - back > max_size eventually.
_GLIBCXX_PARALLEL_ASSERT(((former_front + 1) - former_back)
<= max_size);
#endif
fetch_and_add(&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(T& t)
{
int former_front, former_back;
#pragma omp flush
decode2(borders, former_front, former_back);
while (former_front > former_back)
{
// Chance.
lcas_t former_borders = encode2(former_front, former_back);
lcas_t new_borders = encode2(former_front - 1, former_back);
if (compare_and_swap(&borders, former_borders, new_borders))
{
t = *(base + (former_front - 1) % max_size);
return true;
}
#pragma omp flush
decode2(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(T& t) //queue behavior
{
int former_front, former_back;
#pragma omp flush
decode2(borders, former_front, former_back);
while (former_front > former_back)
{
// Chance.
lcas_t former_borders = encode2(former_front, former_back);
lcas_t new_borders = encode2(former_front, former_back + 1);
if (compare_and_swap(&borders, former_borders, new_borders))
{
t = *(base + former_back % max_size);
return true;
}
#pragma omp flush
decode2(borders, former_front, former_back);
}
return false;
}
};
} //namespace __gnu_parallel
#undef _GLIBCXX_VOLATILE
#endif /* _GLIBCXX_PARALLEL_QUEUE_H */
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