Alc/ringbuffer.c

   1 /**
   2  * OpenAL cross platform audio library
   3  * Copyright (C) 1999-2007 by authors.
   4  * This library is free software; you can redistribute it and/or
   5  *  modify it under the terms of the GNU Library General Public
   6  *  License as published by the Free Software Foundation; either
   7  *  version 2 of the License, or (at your option) any later version.
   8  *
   9  * This library is distributed in the hope that it will be useful,
  10  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  *  Library General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU Library General Public
  15  *  License along with this library; if not, write to the
  16  *  Free Software Foundation, Inc.,
  17  *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  18  * Or go to http://www.gnu.org/copyleft/lgpl.html
  19  */
  20
  21 #include "config.h"
  22
  23 #include <string.h>
  24 #include <stdlib.h>
  25
  26 #include "ringbuffer.h"
  27 #include "align.h"
  28 #include "atomic.h"
  29 #include "threads.h"
  30 #include "almalloc.h"
  31 #include "compat.h"
  32
  33
  34 /* NOTE: This lockless ringbuffer implementation is copied from JACK, extended
  35  * to include an element size. Consequently, parameters and return values for a
  36  * size or count is in 'elements', not bytes. Additionally, it only supports
  37  * single-consumer/single-provider operation. */
  38 struct ll_ringbuffer {
  39     ATOMIC(size_t) write_ptr;
  40     ATOMIC(size_t) read_ptr;
  41     size_t size;
  42     size_t size_mask;
  43     size_t elem_size;
  44
  45     alignas(16) char buf[];
  46 };
  47
  48 /* Create a new ringbuffer to hold at least `sz' elements of `elem_sz' bytes.
  49  * The number of elements is rounded up to the next power of two. */
  50 ll_ringbuffer_t *ll_ringbuffer_create(size_t sz, size_t elem_sz)
  51 {
  52     ll_ringbuffer_t *rb;
  53     size_t power_of_two = 0;
  54
  55     if(sz > 0)
  56     {
  57         power_of_two = sz - 1;
  58         power_of_two |= power_of_two>>1;
  59         power_of_two |= power_of_two>>2;
  60         power_of_two |= power_of_two>>4;
  61         power_of_two |= power_of_two>>8;
  62         power_of_two |= power_of_two>>16;
  63 #if SIZE_MAX > UINT_MAX
  64         power_of_two |= power_of_two>>32;
  65 #endif
  66     }
  67     power_of_two++;
  68     if(power_of_two < sz) return NULL;
  69
  70     rb = al_malloc(16, sizeof(*rb) + power_of_two*elem_sz);
  71     if(!rb) return NULL;
  72
  73     ATOMIC_INIT(&rb->write_ptr, 0);
  74     ATOMIC_INIT(&rb->read_ptr, 0);
  75     rb->size = power_of_two;
  76     rb->size_mask = rb->size - 1;
  77     rb->elem_size = elem_sz;
  78     return rb;
  79 }
  80
  81 /* Free all data associated with the ringbuffer `rb'. */
  82 void ll_ringbuffer_free(ll_ringbuffer_t *rb)
  83 {
  84     al_free(rb);
  85 }
  86
  87 /* Reset the read and write pointers to zero. This is not thread safe. */
  88 void ll_ringbuffer_reset(ll_ringbuffer_t *rb)
  89 {
  90     ATOMIC_STORE(&rb->write_ptr, 0, almemory_order_release);
  91     ATOMIC_STORE(&rb->read_ptr, 0, almemory_order_release);
  92     memset(rb->buf, 0, rb->size*rb->elem_size);
  93 }
  94
  95 /* Return the number of elements available for reading. This is the number of
  96  * elements in front of the read pointer and behind the write pointer. */
  97 size_t ll_ringbuffer_read_space(const ll_ringbuffer_t *rb)
  98 {
  99     size_t w = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->write_ptr, almemory_order_acquire);
 100     size_t r = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->read_ptr, almemory_order_acquire);
 101     return (w-r) & rb->size_mask;
 102 }
 103 /* Return the number of elements available for writing. This is the number of
 104  * elements in front of the write pointer and behind the read pointer. */
 105 size_t ll_ringbuffer_write_space(const ll_ringbuffer_t *rb)
 106 {
 107     size_t w = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->write_ptr, almemory_order_acquire);
 108     size_t r = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->read_ptr, almemory_order_acquire);
 109     return (r-w-1) & rb->size_mask;
 110 }
 111
 112 /* The copying data reader. Copy at most `cnt' elements from `rb' to `dest'.
 113  * Returns the actual number of elements copied. */
 114 size_t ll_ringbuffer_read(ll_ringbuffer_t *rb, char *dest, size_t cnt)
 115 {
 116     size_t read_ptr;
 117     size_t free_cnt;
 118     size_t cnt2;
 119     size_t to_read;
 120     size_t n1, n2;
 121
 122     free_cnt = ll_ringbuffer_read_space(rb);
 123     if(free_cnt == 0) return 0;
 124
 125     to_read = (cnt > free_cnt) ? free_cnt : cnt;
 126     read_ptr = ATOMIC_LOAD(&rb->read_ptr, almemory_order_relaxed) & rb->size_mask;
 127
 128     cnt2 = read_ptr + to_read;
 129     if(cnt2 > rb->size)
 130     {
 131         n1 = rb->size - read_ptr;
 132         n2 = cnt2 & rb->size_mask;
 133     }
 134     else
 135     {
 136         n1 = to_read;
 137         n2 = 0;
 138     }
 139
 140     memcpy(dest, &rb->buf[read_ptr*rb->elem_size], n1*rb->elem_size);
 141     read_ptr += n1;
 142     if(n2)
 143     {
 144         memcpy(dest + n1*rb->elem_size, &rb->buf[(read_ptr&rb->size_mask)*rb->elem_size],
 145                n2*rb->elem_size);
 146         read_ptr += n2;
 147     }
 148     ATOMIC_STORE(&rb->read_ptr, read_ptr, almemory_order_release);
 149     return to_read;
 150 }
 151
 152 /* The copying data reader w/o read pointer advance. Copy at most `cnt'
 153  * elements from `rb' to `dest'. Returns the actual number of elements copied.
 154  */
 155 size_t ll_ringbuffer_peek(ll_ringbuffer_t *rb, char *dest, size_t cnt)
 156 {
 157     size_t free_cnt;
 158     size_t cnt2;
 159     size_t to_read;
 160     size_t n1, n2;
 161     size_t read_ptr;
 162
 163     free_cnt = ll_ringbuffer_read_space(rb);
 164     if(free_cnt == 0) return 0;
 165
 166     to_read = (cnt > free_cnt) ? free_cnt : cnt;
 167     read_ptr = ATOMIC_LOAD(&rb->read_ptr, almemory_order_relaxed) & rb->size_mask;
 168
 169     cnt2 = read_ptr + to_read;
 170     if(cnt2 > rb->size)
 171     {
 172         n1 = rb->size - read_ptr;
 173         n2 = cnt2 & rb->size_mask;
 174     }
 175     else
 176     {
 177         n1 = to_read;
 178         n2 = 0;
 179     }
 180
 181     memcpy(dest, &rb->buf[read_ptr*rb->elem_size], n1*rb->elem_size);
 182     if(n2)
 183     {
 184         read_ptr += n1;
 185         memcpy(dest + n1*rb->elem_size, &rb->buf[(read_ptr&rb->size_mask)*rb->elem_size],
 186                n2*rb->elem_size);
 187     }
 188     return to_read;
 189 }
 190
 191 /* The copying data writer. Copy at most `cnt' elements to `rb' from `src'.
 192  * Returns the actual number of elements copied. */
 193 size_t ll_ringbuffer_write(ll_ringbuffer_t *rb, const char *src, size_t cnt)
 194 {
 195     size_t write_ptr;
 196     size_t free_cnt;
 197     size_t cnt2;
 198     size_t to_write;
 199     size_t n1, n2;
 200
 201     free_cnt = ll_ringbuffer_write_space(rb);
 202     if(free_cnt == 0) return 0;
 203
 204     to_write = (cnt > free_cnt) ? free_cnt : cnt;
 205     write_ptr = ATOMIC_LOAD(&rb->write_ptr, almemory_order_relaxed) & rb->size_mask;
 206
 207     cnt2 = write_ptr + to_write;
 208     if(cnt2 > rb->size)
 209     {
 210         n1 = rb->size - write_ptr;
 211         n2 = cnt2 & rb->size_mask;
 212     }
 213     else
 214     {
 215         n1 = to_write;
 216         n2 = 0;
 217     }
 218
 219     memcpy(&rb->buf[write_ptr*rb->elem_size], src, n1*rb->elem_size);
 220     write_ptr += n1;
 221     if(n2)
 222     {
 223         memcpy(&rb->buf[(write_ptr&rb->size_mask)*rb->elem_size], src + n1*rb->elem_size,
 224                n2*rb->elem_size);
 225         write_ptr += n2;
 226     }
 227     ATOMIC_STORE(&rb->write_ptr, write_ptr, almemory_order_release);
 228     return to_write;
 229 }
 230
 231 /* Advance the read pointer `cnt' places. */
 232 void ll_ringbuffer_read_advance(ll_ringbuffer_t *rb, size_t cnt)
 233 {
 234     ATOMIC_ADD(&rb->read_ptr, cnt, almemory_order_acq_rel);
 235 }
 236
 237 /* Advance the write pointer `cnt' places. */
 238 void ll_ringbuffer_write_advance(ll_ringbuffer_t *rb, size_t cnt)
 239 {
 240     ATOMIC_ADD(&rb->write_ptr, cnt, almemory_order_acq_rel);
 241 }
 242
 243 /* The non-copying data reader. `vec' is an array of two places. Set the values
 244  * at `vec' to hold the current readable data at `rb'. If the readable data is
 245  * in one segment the second segment has zero length. */
 246 void ll_ringbuffer_get_read_vector(const ll_ringbuffer_t *rb, ll_ringbuffer_data_t * vec)
 247 {
 248     size_t free_cnt;
 249     size_t cnt2;
 250     size_t w, r;
 251
 252     w = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->write_ptr, almemory_order_acquire);
 253     r = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->read_ptr, almemory_order_acquire);
 254     w &= rb->size_mask;
 255     r &= rb->size_mask;
 256     free_cnt = (w-r) & rb->size_mask;
 257
 258     cnt2 = r + free_cnt;
 259     if(cnt2 > rb->size)
 260     {
 261         /* Two part vector: the rest of the buffer after the current write ptr,
 262          * plus some from the start of the buffer. */
 263         vec[0].buf = (char*)&rb->buf[r*rb->elem_size];
 264         vec[0].len = rb->size - r;
 265         vec[1].buf = (char*)rb->buf;
 266         vec[1].len = cnt2 & rb->size_mask;
 267     }
 268     else
 269     {
 270         /* Single part vector: just the rest of the buffer */
 271         vec[0].buf = (char*)&rb->buf[r*rb->elem_size];
 272         vec[0].len = free_cnt;
 273         vec[1].buf = NULL;
 274         vec[1].len = 0;
 275     }
 276 }
 277
 278 /* The non-copying data writer. `vec' is an array of two places. Set the values
 279  * at `vec' to hold the current writeable data at `rb'. If the writeable data
 280  * is in one segment the second segment has zero length. */
 281 void ll_ringbuffer_get_write_vector(const ll_ringbuffer_t *rb, ll_ringbuffer_data_t *vec)
 282 {
 283     size_t free_cnt;
 284     size_t cnt2;
 285     size_t w, r;
 286
 287     w = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->write_ptr, almemory_order_acquire);
 288     r = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->read_ptr, almemory_order_acquire);
 289     w &= rb->size_mask;
 290     r &= rb->size_mask;
 291     free_cnt = (r-w-1) & rb->size_mask;
 292
 293     cnt2 = w + free_cnt;
 294     if(cnt2 > rb->size)
 295     {
 296         /* Two part vector: the rest of the buffer after the current write ptr,
 297          * plus some from the start of the buffer. */
 298         vec[0].buf = (char*)&rb->buf[w*rb->elem_size];
 299         vec[0].len = rb->size - w;
 300         vec[1].buf = (char*)rb->buf;
 301         vec[1].len = cnt2 & rb->size_mask;
 302     }
 303     else
 304     {
 305         vec[0].buf = (char*)&rb->buf[w*rb->elem_size];
 306         vec[0].len = free_cnt;
 307         vec[1].buf = NULL;
 308         vec[1].len = 0;
 309     }
 310 }