add a lock-free bounded spsc interthread queue

Not entirely wait-free: allows waiting on a fd, and in general fd
notifications for poll-loop integration between threads.

Change-Id: I4f17042baf76d086ce6b20eb99402dc64c22c657
This commit is contained in:
Eric Wild 2021-09-06 20:07:24 +02:00 committed by laforge
parent ee6958c9a8
commit e03e34f8bb
2 changed files with 259 additions and 0 deletions

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/*
* (C) 2021 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
* All Rights Reserved
*
* Author: Eric Wild
*
* 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 <stdatomic.h>
#include <stdbool.h>
#include <stdlib.h>
struct spsc {
atomic_uint readptr;
atomic_uint writeptr;
int efd_r, efd_w; /* eventfds used to block/notify readers/writers */
int count;
int size_per_buf;
void *buf; /* buffer size count*size_per_buf */
uintptr_t data[0]; /* count sized array of pointers to size_per_buf chunks in buf array*/
};
struct qchan {
struct spsc *a;
struct spsc *b;
};
bool spsc_push(struct spsc *q, void *elem);
bool spsc_pop(struct spsc *q, void *elem);
ssize_t spsc_prep_pop(struct spsc *q);
int spsc_get_a_rdfd(struct qchan *q);
struct qchan spsc_chan_init(void *talloc_ctx, unsigned int count, unsigned int size_per_buf);
struct qchan spsc_chan_init_ex(void *talloc_ctx, unsigned int count, unsigned int size_per_buf, bool blockr_a,
bool blockw_a, bool blockr_b, bool blockw_b);
void spsc_chan_close(struct qchan *q);

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/*
* (C) 2021 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
* All Rights Reserved
*
* Author: Eric Wild
*
* 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 <inttypes.h>
#include <stdatomic.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <sys/eventfd.h>
#include <sys/types.h>
#include <unistd.h>
#include <talloc.h>
#include <osmocom/mgcp/mgcp_threads_queue.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
*/
static struct spsc *spsc_init(void *talloc_ctx, unsigned int count, unsigned int size_per_buf, bool blockr, bool blockw)
{
struct spsc *q = talloc_zero_size(talloc_ctx, sizeof(struct spsc) + sizeof(uintptr_t) * count);
atomic_init(&q->readptr, 0);
atomic_init(&q->writeptr, 0);
q->efd_r = eventfd(0, blockr ? 0 : EFD_NONBLOCK);
q->efd_w = eventfd(1, blockw ? 0 : EFD_NONBLOCK);
q->count = count;
q->size_per_buf = size_per_buf;
q->buf = talloc_zero_size(q, size_per_buf * count);
for (int i = 0; i < count; i++)
q->data[i] = (uintptr_t)q->buf + i * size_per_buf;
return q;
}
static void spsc_deinit(struct spsc *q)
{
talloc_free(q->buf);
close(q->efd_r);
close(q->efd_w);
talloc_free(q);
}
static ssize_t spsc_check_r(struct spsc *q)
{
uint64_t efdr;
return read(q->efd_r, &efdr, sizeof(uint64_t));
}
static ssize_t spsc_check_w(struct spsc *q)
{
uint64_t efdr;
return read(q->efd_w, &efdr, sizeof(uint64_t));
}
static void spsc_notify_r(struct spsc *q)
{
uint64_t efdu = 1;
write(q->efd_r, &efdu, sizeof(uint64_t));
}
static void spsc_notify_w(struct spsc *q)
{
uint64_t efdu = 1;
write(q->efd_w, &efdu, sizeof(uint64_t));
}
/*! Adds element to the queue by copying the data.
* \param[in] q queue.
* \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(struct spsc *q, void *elem)
{
size_t cur_wp, cur_rp;
cur_wp = atomic_load_explicit(&q->writeptr, memory_order_relaxed);
cur_rp = atomic_load_explicit(&q->readptr, memory_order_acquire);
if ((cur_wp + 1) % q->count == cur_rp) {
spsc_check_w(q); /* blocks, ensures next (!) call succeeds */
return false;
}
memcpy((void *)q->data[cur_wp], elem, q->size_per_buf);
atomic_store_explicit(&q->writeptr, (cur_wp + 1) % q->count, memory_order_release);
spsc_notify_r(q); /* fine after release */
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.
* \param[in] q queue.
* \returns result of reading the fd. */
ssize_t spsc_prep_pop(struct spsc *q)
{
return spsc_check_r(q);
}
/*! Removes element from the queue by copying the data.
* \param[in] q queue.
* \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(struct spsc *q, void *elem)
{
size_t cur_wp, cur_rp;
cur_wp = atomic_load_explicit(&q->writeptr, memory_order_acquire);
cur_rp = atomic_load_explicit(&q->readptr, memory_order_relaxed);
if (cur_wp == cur_rp) /* blocks via prep_pop */
return false;
memcpy(elem, (void *)q->data[cur_rp], q->size_per_buf);
atomic_store_explicit(&q->readptr, (cur_rp + 1) % q->count, memory_order_release);
spsc_notify_w(q);
return true;
}
/*! Creates a bidirectional queue channel that consists of two queues, one in each direction,
* commonly referred to as a and b side.
* \param[in] talloc_ctx allocation context.
* \param[in] count number of buffers per queue.
* \param[in] size_per_buf size of buffers per queue.
* \param[in] blockr_a should reading the a-side read fd block?.
* \param[in] blockw_a should reading the a-side write fd block?.
* \param[in] blockr_b should reading the b-side read fd block?.
* \param[in] blockw_b should reading the b-side write fd block?.
* \returns queue channel */
struct qchan spsc_chan_init_ex(void *talloc_ctx, unsigned int count, unsigned int size_per_buf, bool blockr_a,
bool blockw_a, bool blockr_b, bool blockw_b)
{
struct qchan q;
q.a = spsc_init(talloc_ctx, count, size_per_buf, blockr_a, blockw_a);
q.b = spsc_init(talloc_ctx, count, size_per_buf, blockr_b, blockw_b);
return q;
}
/*! Creates a bidirectional queue channel that consists of two queues, one in each direction,
* commonly referred to as a and b side.
* \param[in] talloc_ctx allocation context.
* \param[in] count number of buffers per queue.
* \param[in] size_per_buf size of buffers per queue.
* \returns queue channel */
struct qchan spsc_chan_init(void *talloc_ctx, unsigned int count, unsigned int size_per_buf)
{
return spsc_chan_init_ex(talloc_ctx, count, size_per_buf, false, true, false, true);
}
/*! Closes a bidirectional queue channel.
* \param[in] q queue */
void spsc_chan_close(struct qchan *q)
{
spsc_deinit(q->a);
spsc_deinit(q->b);
free(q);
}
/*! Gets queue channel read/write fd for a/b side according to function name.
* \param[in] q queue channel.
* \returns fd */
int spsc_get_a_rdfd(struct qchan *q)
{
return q->a->efd_r;
}
/*! Gets queue channel read/write fd for a/b side according to function name.
* \param[in] q queue channel.
* \returns fd */
int spsc_get_b_rdfd(struct qchan *q)
{
return q->b->efd_r;
}
/*! Gets queue channel read/write fd for a/b side according to function name.
* \param[in] q queue channel.
* \returns fd */
int spsc_get_a_wrfd(struct qchan *q)
{
return q->a->efd_w;
}
/*! Gets queue channel read/write fd for a/b side according to function name.
* \param[in] q queue channel.
* \returns fd */
int spsc_get_b_wrfd(struct qchan *q)
{
return q->b->efd_w;
}