204 lines
5.2 KiB
C++
204 lines
5.2 KiB
C++
#pragma once
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/*
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* (C) 2022 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
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* All Rights Reserved
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*
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* Author: Eric Wild <ewild@sysmocom.de>
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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 Affero General Public License as published by
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* the Free Software Foundation; either version 3 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 Affero General Public License for more details.
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*
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* You should have received a copy of the GNU Affero General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*
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*/
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#include <atomic>
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#include <condition_variable>
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#include <mutex>
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#include <sys/eventfd.h>
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#include <unistd.h>
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#include <stdatomic.h>
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#include <stdbool.h>
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#include <stdlib.h>
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/*
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classic lamport circular lockfree spsc queue:
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every "side" only writes its own ptr, but may read the other sides ptr
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notify reader using eventfd as soon as element is added, reader then reads until
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read fails
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-> reader pops in a loop until FALSE and might get spurious events because it
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read before it was notified, which is fine
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-> writing pushes *the same data* in a loop until TRUE, blocks
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shutting this down requires
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1) to stop reading and pushing
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2) ONE side to take care of the eventfds
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*/
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namespace spsc_detail
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{
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template <bool block_read, bool block_write> class spsc_cond_detail {
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std::condition_variable cond_r, cond_w;
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std::mutex l;
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public:
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explicit spsc_cond_detail()
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{
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}
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~spsc_cond_detail()
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{
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}
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ssize_t spsc_check_r()
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{
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std::unique_lock<std::mutex> lk(l);
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cond_r.wait(lk);
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return 1;
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}
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ssize_t spsc_check_w()
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{
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std::unique_lock<std::mutex> lk(l);
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cond_w.wait(lk);
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return 1;
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}
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void spsc_notify_r()
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{
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cond_r.notify_one();
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}
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void spsc_notify_w()
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{
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cond_w.notify_one();
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}
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};
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// originally designed for select loop integration
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template <bool block_read, bool block_write> class spsc_efd_detail {
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int efd_r, efd_w; /* eventfds used to block/notify readers/writers */
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public:
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explicit spsc_efd_detail()
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: efd_r(eventfd(0, block_read ? 0 : EFD_NONBLOCK)), efd_w(eventfd(1, block_write ? 0 : EFD_NONBLOCK))
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{
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}
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~spsc_efd_detail()
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{
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close(efd_r);
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close(efd_w);
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}
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ssize_t spsc_check_r()
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{
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uint64_t efdr;
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return read(efd_r, &efdr, sizeof(uint64_t));
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}
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ssize_t spsc_check_w()
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{
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uint64_t efdr;
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return read(efd_w, &efdr, sizeof(uint64_t));
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}
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void spsc_notify_r()
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{
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uint64_t efdu = 1;
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write(efd_r, &efdu, sizeof(uint64_t));
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}
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void spsc_notify_w()
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{
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uint64_t efdu = 1;
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write(efd_w, &efdu, sizeof(uint64_t));
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}
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int get_r_efd()
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{
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return efd_r;
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}
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int get_w_efd()
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{
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return efd_w;
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}
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};
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template <unsigned int SZ, typename ELEM, bool block_read, bool block_write, template <bool, bool> class T>
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class spsc : public T<block_read, block_write> {
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static_assert(SZ > 0, "queues need a size...");
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std::atomic<unsigned int> readptr;
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std::atomic<unsigned int> writeptr;
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ELEM buf[SZ];
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public:
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using base_t = T<block_read, block_write>;
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using elem_t = ELEM;
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explicit spsc() : readptr(0), writeptr(0)
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{
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}
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~spsc()
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{
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}
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/*! Adds element to the queue by copying the data.
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* \param[in] elem input buffer, must match the originally configured queue buffer size!.
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* \returns true if queue was not full and element was successfully pushed */
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bool spsc_push(ELEM *elem)
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{
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size_t cur_wp, cur_rp;
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cur_wp = writeptr.load(std::memory_order_relaxed);
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cur_rp = readptr.load(std::memory_order_acquire);
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if ((cur_wp + 1) % SZ == cur_rp) {
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if (block_write)
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base_t::spsc_check_w(); /* blocks, ensures next (!) call succeeds */
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return false;
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}
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buf[cur_wp] = *elem;
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writeptr.store((cur_wp + 1) % SZ, std::memory_order_release);
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if (block_read)
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base_t::spsc_notify_r(); /* fine after release */
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return true;
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}
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/*! Removes element from the queue by copying the data.
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* \param[in] elem output buffer, must match the originally configured queue buffer size!.
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* \returns true if queue was not empty and element was successfully removed */
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bool spsc_pop(ELEM *elem)
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{
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size_t cur_wp, cur_rp;
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cur_wp = writeptr.load(std::memory_order_acquire);
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cur_rp = readptr.load(std::memory_order_relaxed);
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if (cur_wp == cur_rp) /* blocks via prep_pop */
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return false;
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*elem = buf[cur_rp];
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readptr.store((cur_rp + 1) % SZ, std::memory_order_release);
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if (block_write)
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base_t::spsc_notify_w();
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return true;
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}
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/*! Reads the read-fd of the queue, which, depending on settings passed on queue creation, blocks.
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* This function can be used to deliberately wait for a non-empty queue on the read side.
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* \returns result of reading the fd. */
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ssize_t spsc_prep_pop()
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{
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return base_t::spsc_check_r();
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}
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};
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} // namespace spsc_detail
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template <unsigned int SZ, typename ELEM, bool block_read, bool block_write>
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class spsc_evfd : public spsc_detail::spsc<SZ, ELEM, block_read, block_write, spsc_detail::spsc_efd_detail> {};
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template <unsigned int SZ, typename ELEM, bool block_read, bool block_write>
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class spsc_cond : public spsc_detail::spsc<SZ, ELEM, block_read, block_write, spsc_detail::spsc_cond_detail> {}; |