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