165 lines
3.9 KiB
C++
165 lines
3.9 KiB
C++
/*
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* Copyright (C) 2010-2011 Dmitry Vyukov
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* Copyright (C) 2019 Robin Gareus <robin@gareus.org>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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#ifndef _pbd_mpc_queue_h_
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#define _pbd_mpc_queue_h_
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#include <cassert>
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#include <stdint.h>
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#include <stdlib.h>
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# include <atomic>
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# define MPMC_QUEUE_TYPE std::atomic<size_t>
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namespace PBD {
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/* Lock free multiple producer, multiple consumer queue
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*
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* Inspired by http://www.1024cores.net/home/lock-free-algorithms/queues/bounded-mpmc-queue
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* Kudos to Dmitry Vyukov who licensed that code in terms of a 2-clause BSD license.
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*/
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template <typename T>
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class /*LIBPBD_API*/ MPMCQueue
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{
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public:
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MPMCQueue (size_t buffer_size = 8)
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: _buffer (0)
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, _buffer_mask (0)
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{
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reserve (buffer_size);
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}
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~MPMCQueue ()
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{
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delete[] _buffer;
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}
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size_t capacity () const {
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return _buffer_mask + 1;
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}
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static size_t
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power_of_two_size (size_t sz)
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{
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int32_t power_of_two;
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for (power_of_two = 1; 1U << power_of_two < sz; ++power_of_two) ;
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return 1U << power_of_two;
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}
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void
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reserve (size_t buffer_size)
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{
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buffer_size = power_of_two_size (buffer_size);
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assert ((buffer_size >= 2) && ((buffer_size & (buffer_size - 1)) == 0));
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if (_buffer_mask >= buffer_size - 1) {
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return;
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}
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delete[] _buffer;
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_buffer = new cell_t[buffer_size];
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_buffer_mask = buffer_size - 1;
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clear ();
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}
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void
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clear ()
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{
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for (size_t i = 0; i <= _buffer_mask; ++i) {
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_buffer[i]._sequence.store (i, std::memory_order_relaxed);
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}
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_enqueue_pos.store (0, std::memory_order_relaxed);
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_dequeue_pos.store (0, std::memory_order_relaxed);
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}
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bool
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push_back (T const& data)
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{
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cell_t* cell;
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size_t pos = _enqueue_pos.load (std::memory_order_relaxed);
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for (;;) {
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cell = &_buffer[pos & _buffer_mask];
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size_t seq = cell->_sequence.load (std::memory_order_acquire);
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intptr_t dif = (intptr_t)seq - (intptr_t)pos;
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if (dif == 0) {
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if (_enqueue_pos.compare_exchange_weak (pos, pos + 1, std::memory_order_relaxed))
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{
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break;
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}
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} else if (dif < 0) {
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return false;
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} else {
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pos = _enqueue_pos.load (std::memory_order_relaxed);
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}
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}
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cell->_data = data;
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cell->_sequence.store (pos + 1, std::memory_order_release);
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return true;
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}
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bool
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pop_front (T& data)
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{
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cell_t* cell;
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size_t pos = _dequeue_pos.load (std::memory_order_relaxed);
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for (;;) {
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cell = &_buffer[pos & _buffer_mask];
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size_t seq = cell->_sequence.load (std::memory_order_acquire);
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intptr_t dif = (intptr_t)seq - (intptr_t) (pos + 1);
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if (dif == 0) {
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if (_dequeue_pos.compare_exchange_weak (pos, pos + 1, std::memory_order_relaxed))
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{
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break;
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}
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} else if (dif < 0) {
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return false;
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} else {
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pos = _dequeue_pos.load (std::memory_order_relaxed);
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}
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}
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data = cell->_data;
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cell->_sequence.store (pos + _buffer_mask + 1, std::memory_order_release);
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return true;
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}
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private:
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struct cell_t {
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MPMC_QUEUE_TYPE _sequence;
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T _data;
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};
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char _pad0[64];
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cell_t* _buffer;
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size_t _buffer_mask;
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char _pad1[64 - sizeof (cell_t*) - sizeof (size_t)];
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MPMC_QUEUE_TYPE _enqueue_pos;
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char _pad2[64 - sizeof (size_t)];
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MPMC_QUEUE_TYPE _dequeue_pos;
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char _pad3[64 - sizeof (size_t)];
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};
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} // namespace PBD
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#undef MPMC_QUEUE_TYPE
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#endif
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