Eric | e03e34f | 2021-09-06 20:07:24 +0200 | [diff] [blame] | 1 | /* |
| 2 | * (C) 2021 by sysmocom s.f.m.c. GmbH <info@sysmocom.de> |
| 3 | * All Rights Reserved |
| 4 | * |
| 5 | * Author: Eric Wild |
| 6 | * |
| 7 | * This program is free software; you can redistribute it and/or modify |
| 8 | * it under the terms of the GNU Affero General Public License as published by |
| 9 | * the Free Software Foundation; either version 3 of the License, or |
| 10 | * (at your option) any later version. |
| 11 | * |
| 12 | * This program is distributed in the hope that it will be useful, |
| 13 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 14 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 15 | * GNU Affero General Public License for more details. |
| 16 | * |
| 17 | * You should have received a copy of the GNU Affero General Public License |
| 18 | * along with this program. If not, see <http://www.gnu.org/licenses/>. |
| 19 | * |
| 20 | */ |
| 21 | |
| 22 | #include <inttypes.h> |
| 23 | #include <stdatomic.h> |
| 24 | #include <stdbool.h> |
| 25 | #include <stdint.h> |
| 26 | #include <stdlib.h> |
| 27 | #include <string.h> |
| 28 | #include <sys/eventfd.h> |
| 29 | #include <sys/types.h> |
| 30 | #include <unistd.h> |
| 31 | #include <talloc.h> |
| 32 | |
| 33 | #include <osmocom/mgcp/mgcp_threads_queue.h> |
| 34 | |
| 35 | /* |
| 36 | classic lamport circular lockfree spsc queue: |
| 37 | every "side" only writes its own ptr, but may read the other sides ptr |
| 38 | |
| 39 | notify reader using eventfd as soon as element is added, reader then reads until |
| 40 | read fails |
| 41 | -> reader pops in a loop until FALSE and might get spurious events because it |
| 42 | read before it was notified, which is fine |
| 43 | -> writing pushes *the same data* in a loop until TRUE, blocks |
| 44 | |
| 45 | shutting this down requires |
| 46 | 1) to stop reading and pushing |
| 47 | 2) ONE side to take care of the eventfds |
| 48 | */ |
| 49 | |
| 50 | static struct spsc *spsc_init(void *talloc_ctx, unsigned int count, unsigned int size_per_buf, bool blockr, bool blockw) |
| 51 | { |
| 52 | struct spsc *q = talloc_zero_size(talloc_ctx, sizeof(struct spsc) + sizeof(uintptr_t) * count); |
| 53 | atomic_init(&q->readptr, 0); |
| 54 | atomic_init(&q->writeptr, 0); |
| 55 | q->efd_r = eventfd(0, blockr ? 0 : EFD_NONBLOCK); |
| 56 | q->efd_w = eventfd(1, blockw ? 0 : EFD_NONBLOCK); |
| 57 | q->count = count; |
| 58 | q->size_per_buf = size_per_buf; |
| 59 | q->buf = talloc_zero_size(q, size_per_buf * count); |
| 60 | |
| 61 | for (int i = 0; i < count; i++) |
| 62 | q->data[i] = (uintptr_t)q->buf + i * size_per_buf; |
| 63 | return q; |
| 64 | } |
| 65 | |
| 66 | static void spsc_deinit(struct spsc *q) |
| 67 | { |
| 68 | talloc_free(q->buf); |
| 69 | close(q->efd_r); |
| 70 | close(q->efd_w); |
| 71 | talloc_free(q); |
| 72 | } |
| 73 | |
| 74 | static ssize_t spsc_check_r(struct spsc *q) |
| 75 | { |
| 76 | uint64_t efdr; |
| 77 | return read(q->efd_r, &efdr, sizeof(uint64_t)); |
| 78 | } |
| 79 | static ssize_t spsc_check_w(struct spsc *q) |
| 80 | { |
| 81 | uint64_t efdr; |
| 82 | return read(q->efd_w, &efdr, sizeof(uint64_t)); |
| 83 | } |
| 84 | static void spsc_notify_r(struct spsc *q) |
| 85 | { |
| 86 | uint64_t efdu = 1; |
| 87 | write(q->efd_r, &efdu, sizeof(uint64_t)); |
| 88 | } |
| 89 | static void spsc_notify_w(struct spsc *q) |
| 90 | { |
| 91 | uint64_t efdu = 1; |
| 92 | write(q->efd_w, &efdu, sizeof(uint64_t)); |
| 93 | } |
| 94 | |
| 95 | /*! Adds element to the queue by copying the data. |
| 96 | * \param[in] q queue. |
| 97 | * \param[in] elem input buffer, must match the originally configured queue buffer size!. |
| 98 | * \returns true if queue was not full and element was successfully pushed */ |
| 99 | bool spsc_push(struct spsc *q, void *elem) |
| 100 | { |
| 101 | size_t cur_wp, cur_rp; |
| 102 | cur_wp = atomic_load_explicit(&q->writeptr, memory_order_relaxed); |
| 103 | cur_rp = atomic_load_explicit(&q->readptr, memory_order_acquire); |
| 104 | if ((cur_wp + 1) % q->count == cur_rp) { |
| 105 | spsc_check_w(q); /* blocks, ensures next (!) call succeeds */ |
| 106 | return false; |
| 107 | } |
| 108 | memcpy((void *)q->data[cur_wp], elem, q->size_per_buf); |
| 109 | atomic_store_explicit(&q->writeptr, (cur_wp + 1) % q->count, memory_order_release); |
| 110 | spsc_notify_r(q); /* fine after release */ |
| 111 | return true; |
| 112 | } |
| 113 | |
| 114 | /*! Reads the read-fd of the queue, which, depending on settings passed on queue creation, blocks. |
| 115 | * This function can be used to deliberately wait for a non-empty queue on the read side. |
| 116 | * \param[in] q queue. |
| 117 | * \returns result of reading the fd. */ |
| 118 | ssize_t spsc_prep_pop(struct spsc *q) |
| 119 | { |
| 120 | return spsc_check_r(q); |
| 121 | } |
| 122 | |
| 123 | /*! Removes element from the queue by copying the data. |
| 124 | * \param[in] q queue. |
| 125 | * \param[in] elem output buffer, must match the originally configured queue buffer size!. |
| 126 | * \returns true if queue was not empty and element was successfully removed */ |
| 127 | bool spsc_pop(struct spsc *q, void *elem) |
| 128 | { |
| 129 | size_t cur_wp, cur_rp; |
| 130 | cur_wp = atomic_load_explicit(&q->writeptr, memory_order_acquire); |
| 131 | cur_rp = atomic_load_explicit(&q->readptr, memory_order_relaxed); |
| 132 | |
| 133 | if (cur_wp == cur_rp) /* blocks via prep_pop */ |
| 134 | return false; |
| 135 | memcpy(elem, (void *)q->data[cur_rp], q->size_per_buf); |
| 136 | atomic_store_explicit(&q->readptr, (cur_rp + 1) % q->count, memory_order_release); |
| 137 | spsc_notify_w(q); |
| 138 | return true; |
| 139 | } |
| 140 | |
| 141 | /*! Creates a bidirectional queue channel that consists of two queues, one in each direction, |
| 142 | * commonly referred to as a and b side. |
| 143 | * \param[in] talloc_ctx allocation context. |
| 144 | * \param[in] count number of buffers per queue. |
| 145 | * \param[in] size_per_buf size of buffers per queue. |
| 146 | * \param[in] blockr_a should reading the a-side read fd block?. |
| 147 | * \param[in] blockw_a should reading the a-side write fd block?. |
| 148 | * \param[in] blockr_b should reading the b-side read fd block?. |
| 149 | * \param[in] blockw_b should reading the b-side write fd block?. |
| 150 | * \returns queue channel */ |
| 151 | struct qchan spsc_chan_init_ex(void *talloc_ctx, unsigned int count, unsigned int size_per_buf, bool blockr_a, |
| 152 | bool blockw_a, bool blockr_b, bool blockw_b) |
| 153 | { |
| 154 | struct qchan q; |
| 155 | q.a = spsc_init(talloc_ctx, count, size_per_buf, blockr_a, blockw_a); |
| 156 | q.b = spsc_init(talloc_ctx, count, size_per_buf, blockr_b, blockw_b); |
| 157 | return q; |
| 158 | } |
| 159 | |
| 160 | /*! Creates a bidirectional queue channel that consists of two queues, one in each direction, |
| 161 | * commonly referred to as a and b side. |
| 162 | * \param[in] talloc_ctx allocation context. |
| 163 | * \param[in] count number of buffers per queue. |
| 164 | * \param[in] size_per_buf size of buffers per queue. |
| 165 | * \returns queue channel */ |
| 166 | struct qchan spsc_chan_init(void *talloc_ctx, unsigned int count, unsigned int size_per_buf) |
| 167 | { |
| 168 | return spsc_chan_init_ex(talloc_ctx, count, size_per_buf, false, true, false, true); |
| 169 | } |
| 170 | |
| 171 | /*! Closes a bidirectional queue channel. |
| 172 | * \param[in] q queue */ |
| 173 | void spsc_chan_close(struct qchan *q) |
| 174 | { |
| 175 | spsc_deinit(q->a); |
| 176 | spsc_deinit(q->b); |
| 177 | free(q); |
| 178 | } |
| 179 | |
| 180 | /*! Gets queue channel read/write fd for a/b side according to function name. |
| 181 | * \param[in] q queue channel. |
| 182 | * \returns fd */ |
| 183 | int spsc_get_a_rdfd(struct qchan *q) |
| 184 | { |
| 185 | return q->a->efd_r; |
| 186 | } |
| 187 | /*! Gets queue channel read/write fd for a/b side according to function name. |
| 188 | * \param[in] q queue channel. |
| 189 | * \returns fd */ |
| 190 | int spsc_get_b_rdfd(struct qchan *q) |
| 191 | { |
| 192 | return q->b->efd_r; |
| 193 | } |
| 194 | /*! Gets queue channel read/write fd for a/b side according to function name. |
| 195 | * \param[in] q queue channel. |
| 196 | * \returns fd */ |
| 197 | int spsc_get_a_wrfd(struct qchan *q) |
| 198 | { |
| 199 | return q->a->efd_w; |
| 200 | } |
| 201 | /*! Gets queue channel read/write fd for a/b side according to function name. |
| 202 | * \param[in] q queue channel. |
| 203 | * \returns fd */ |
| 204 | int spsc_get_b_wrfd(struct qchan *q) |
| 205 | { |
| 206 | return q->b->efd_w; |
| 207 | } |