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: I4f17042baf76d086ce6b20eb99402dc64c22c657changes/31/25431/23
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/*
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* (C) 2021 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
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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 <stdatomic.h>
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#include <stdbool.h>
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#include <stdlib.h>
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struct spsc {
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atomic_uint readptr;
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atomic_uint writeptr;
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int efd_r, efd_w; /* eventfds used to block/notify readers/writers */
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int count;
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int size_per_buf;
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void *buf; /* buffer size count*size_per_buf */
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uintptr_t data[0]; /* count sized array of pointers to size_per_buf chunks in buf array*/
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};
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struct qchan {
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struct spsc *a;
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struct spsc *b;
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};
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bool spsc_push(struct spsc *q, void *elem);
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bool spsc_pop(struct spsc *q, void *elem);
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ssize_t spsc_prep_pop(struct spsc *q);
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int spsc_get_a_rdfd(struct qchan *q);
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struct qchan spsc_chan_init(void *talloc_ctx, unsigned int count, unsigned int size_per_buf);
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struct qchan spsc_chan_init_ex(void *talloc_ctx, unsigned int count, unsigned int size_per_buf, bool blockr_a,
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bool blockw_a, bool blockr_b, bool blockw_b);
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void spsc_chan_close(struct qchan *q);
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@ -0,0 +1,207 @@
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/*
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* (C) 2021 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
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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 <inttypes.h>
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#include <stdatomic.h>
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#include <stdbool.h>
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#include <stdint.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/eventfd.h>
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#include <sys/types.h>
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#include <unistd.h>
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#include <talloc.h>
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#include <osmocom/mgcp/mgcp_threads_queue.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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static struct spsc *spsc_init(void *talloc_ctx, unsigned int count, unsigned int size_per_buf, bool blockr, bool blockw)
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{
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struct spsc *q = talloc_zero_size(talloc_ctx, sizeof(struct spsc) + sizeof(uintptr_t) * count);
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atomic_init(&q->readptr, 0);
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atomic_init(&q->writeptr, 0);
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q->efd_r = eventfd(0, blockr ? 0 : EFD_NONBLOCK);
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q->efd_w = eventfd(1, blockw ? 0 : EFD_NONBLOCK);
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q->count = count;
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q->size_per_buf = size_per_buf;
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q->buf = talloc_zero_size(q, size_per_buf * count);
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for (int i = 0; i < count; i++)
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q->data[i] = (uintptr_t)q->buf + i * size_per_buf;
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return q;
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}
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static void spsc_deinit(struct spsc *q)
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{
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talloc_free(q->buf);
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close(q->efd_r);
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close(q->efd_w);
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talloc_free(q);
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}
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static ssize_t spsc_check_r(struct spsc *q)
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{
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uint64_t efdr;
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return read(q->efd_r, &efdr, sizeof(uint64_t));
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}
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static ssize_t spsc_check_w(struct spsc *q)
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{
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uint64_t efdr;
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return read(q->efd_w, &efdr, sizeof(uint64_t));
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}
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static void spsc_notify_r(struct spsc *q)
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{
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uint64_t efdu = 1;
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write(q->efd_r, &efdu, sizeof(uint64_t));
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}
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static void spsc_notify_w(struct spsc *q)
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{
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uint64_t efdu = 1;
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write(q->efd_w, &efdu, sizeof(uint64_t));
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}
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/*! Adds element to the queue by copying the data.
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* \param[in] q queue.
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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(struct spsc *q, void *elem)
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{
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size_t cur_wp, cur_rp;
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cur_wp = atomic_load_explicit(&q->writeptr, memory_order_relaxed);
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cur_rp = atomic_load_explicit(&q->readptr, memory_order_acquire);
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if ((cur_wp + 1) % q->count == cur_rp) {
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spsc_check_w(q); /* blocks, ensures next (!) call succeeds */
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return false;
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}
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memcpy((void *)q->data[cur_wp], elem, q->size_per_buf);
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atomic_store_explicit(&q->writeptr, (cur_wp + 1) % q->count, memory_order_release);
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spsc_notify_r(q); /* fine after release */
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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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* \param[in] q queue.
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* \returns result of reading the fd. */
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ssize_t spsc_prep_pop(struct spsc *q)
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{
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return spsc_check_r(q);
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}
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/*! Removes element from the queue by copying the data.
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* \param[in] q queue.
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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(struct spsc *q, void *elem)
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{
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size_t cur_wp, cur_rp;
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cur_wp = atomic_load_explicit(&q->writeptr, memory_order_acquire);
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cur_rp = atomic_load_explicit(&q->readptr, 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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memcpy(elem, (void *)q->data[cur_rp], q->size_per_buf);
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atomic_store_explicit(&q->readptr, (cur_rp + 1) % q->count, memory_order_release);
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spsc_notify_w(q);
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return true;
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}
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/*! Creates a bidirectional queue channel that consists of two queues, one in each direction,
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* commonly referred to as a and b side.
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* \param[in] talloc_ctx allocation context.
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* \param[in] count number of buffers per queue.
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* \param[in] size_per_buf size of buffers per queue.
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* \param[in] blockr_a should reading the a-side read fd block?.
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* \param[in] blockw_a should reading the a-side write fd block?.
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* \param[in] blockr_b should reading the b-side read fd block?.
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* \param[in] blockw_b should reading the b-side write fd block?.
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* \returns queue channel */
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struct qchan spsc_chan_init_ex(void *talloc_ctx, unsigned int count, unsigned int size_per_buf, bool blockr_a,
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bool blockw_a, bool blockr_b, bool blockw_b)
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{
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struct qchan q;
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q.a = spsc_init(talloc_ctx, count, size_per_buf, blockr_a, blockw_a);
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q.b = spsc_init(talloc_ctx, count, size_per_buf, blockr_b, blockw_b);
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return q;
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}
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/*! Creates a bidirectional queue channel that consists of two queues, one in each direction,
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* commonly referred to as a and b side.
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* \param[in] talloc_ctx allocation context.
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* \param[in] count number of buffers per queue.
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* \param[in] size_per_buf size of buffers per queue.
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* \returns queue channel */
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struct qchan spsc_chan_init(void *talloc_ctx, unsigned int count, unsigned int size_per_buf)
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{
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return spsc_chan_init_ex(talloc_ctx, count, size_per_buf, false, true, false, true);
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}
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/*! Closes a bidirectional queue channel.
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* \param[in] q queue */
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void spsc_chan_close(struct qchan *q)
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{
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spsc_deinit(q->a);
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spsc_deinit(q->b);
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free(q);
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}
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/*! Gets queue channel read/write fd for a/b side according to function name.
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* \param[in] q queue channel.
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* \returns fd */
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int spsc_get_a_rdfd(struct qchan *q)
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{
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return q->a->efd_r;
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}
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/*! Gets queue channel read/write fd for a/b side according to function name.
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* \param[in] q queue channel.
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* \returns fd */
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int spsc_get_b_rdfd(struct qchan *q)
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{
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return q->b->efd_r;
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}
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/*! Gets queue channel read/write fd for a/b side according to function name.
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* \param[in] q queue channel.
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* \returns fd */
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int spsc_get_a_wrfd(struct qchan *q)
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{
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return q->a->efd_w;
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}
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/*! Gets queue channel read/write fd for a/b side according to function name.
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* \param[in] q queue channel.
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* \returns fd */
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int spsc_get_b_wrfd(struct qchan *q)
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{
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return q->b->efd_w;
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}
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