Alc/alcRing.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 "alMain.h"
  27 #include "threads.h"
  28 #include "almalloc.h"
  29 #include "compat.h"
  30
  31
  32 /* NOTE: This lockless ringbuffer implementation is copied from JACK, extended
  33  * to include an element size. Consequently, parameters and return values for a
  34  * size or count is in 'elements', not bytes. Additionally, it only supports
  35  * single-consumer/single-provider operation. */
  36 struct ll_ringbuffer {
  37     ATOMIC(size_t) write_ptr;
  38     ATOMIC(size_t) read_ptr;
  39     size_t size;
  40     size_t size_mask;
  41     size_t elem_size;
  42     int mlocked;
  43
  44     alignas(16) char buf[];
  45 };
  46
  47 /* Create a new ringbuffer to hold at least `sz' elements of `elem_sz' bytes.
  48  * The number of elements is rounded up to the next power of two. */
  49 ll_ringbuffer_t *ll_ringbuffer_create(size_t sz, size_t elem_sz)
  50 {
  51     ll_ringbuffer_t *rb;
  52     ALuint power_of_two;
  53
  54     power_of_two = NextPowerOf2(sz);
  55     if(power_of_two < sz)
  56         return NULL;
  57
  58     rb = al_malloc(16, sizeof(*rb) + power_of_two*elem_sz);
  59     if(!rb) return NULL;
  60
  61     ATOMIC_INIT(&rb->write_ptr, 0);
  62     ATOMIC_INIT(&rb->read_ptr, 0);
  63     rb->size = power_of_two;
  64     rb->size_mask = rb->size - 1;
  65     rb->elem_size = elem_sz;
  66     rb->mlocked = 0;
  67     return rb;
  68 }
  69
  70 /* Free all data associated with the ringbuffer `rb'. */
  71 void ll_ringbuffer_free(ll_ringbuffer_t *rb)
  72 {
  73     if(rb)
  74     {
  75 #ifdef USE_MLOCK
  76         if(rb->mlocked)
  77             munlock(rb, sizeof(*rb) + rb->size*rb->elem_size);
  78 #endif /* USE_MLOCK */
  79         al_free(rb);
  80     }
  81 }
  82
  83 /* Lock the data block of `rb' using the system call 'mlock'. */
  84 int ll_ringbuffer_mlock(ll_ringbuffer_t *rb)
  85 {
  86 #ifdef USE_MLOCK
  87     if(!rb->mlocked && mlock(rb, sizeof(*rb) + rb->size*rb->elem_size))
  88         return -1;
  89 #endif /* USE_MLOCK */
  90     rb->mlocked = 1;
  91     return 0;
  92 }
  93
  94 /* Reset the read and write pointers to zero. This is not thread safe. */
  95 void ll_ringbuffer_reset(ll_ringbuffer_t *rb)
  96 {
  97     ATOMIC_STORE(&rb->write_ptr, 0, almemory_order_release);
  98     ATOMIC_STORE(&rb->read_ptr, 0, almemory_order_release);
  99     memset(rb->buf, 0, rb->size*rb->elem_size);
 100 }
 101
 102 /* Return the number of elements available for reading. This is the number of
 103  * elements in front of the read pointer and behind the write pointer. */
 104 size_t ll_ringbuffer_read_space(const ll_ringbuffer_t *rb)
 105 {
 106     size_t w = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->write_ptr, almemory_order_acquire);
 107     size_t r = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->read_ptr, almemory_order_acquire);
 108     return (w-r) & rb->size_mask;
 109 }
 110 /* Return the number of elements available for writing. This is the number of
 111  * elements in front of the write pointer and behind the read pointer. */
 112 size_t ll_ringbuffer_write_space(const ll_ringbuffer_t *rb)
 113 {
 114     size_t w = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->write_ptr, almemory_order_acquire);
 115     size_t r = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->read_ptr, almemory_order_acquire);
 116     return (r-w-1) & rb->size_mask;
 117 }
 118
 119 /* The copying data reader. Copy at most `cnt' elements from `rb' to `dest'.
 120  * Returns the actual number of elements copied. */
 121 size_t ll_ringbuffer_read(ll_ringbuffer_t *rb, char *dest, size_t cnt)
 122 {
 123     size_t read_ptr;
 124     size_t free_cnt;
 125     size_t cnt2;
 126     size_t to_read;
 127     size_t n1, n2;
 128
 129     free_cnt = ll_ringbuffer_read_space(rb);
 130     if(free_cnt == 0) return 0;
 131
 132     to_read = (cnt > free_cnt) ? free_cnt : cnt;
 133     read_ptr = ATOMIC_LOAD(&rb->read_ptr, almemory_order_relaxed) & rb->size_mask;
 134
 135     cnt2 = read_ptr + to_read;
 136     if(cnt2 > rb->size)
 137     {
 138         n1 = rb->size - read_ptr;
 139         n2 = cnt2 & rb->size_mask;
 140     }
 141     else
 142     {
 143         n1 = to_read;
 144         n2 = 0;
 145     }
 146
 147     memcpy(dest, &rb->buf[read_ptr*rb->elem_size], n1*rb->elem_size);
 148     read_ptr += n1;
 149     if(n2)
 150     {
 151         memcpy(dest + n1*rb->elem_size, &rb->buf[(read_ptr&rb->size_mask)*rb->elem_size],
 152                n2*rb->elem_size);
 153         read_ptr += n2;
 154     }
 155     ATOMIC_STORE(&rb->read_ptr, read_ptr, almemory_order_release);
 156     return to_read;
 157 }
 158
 159 /* The copying data reader w/o read pointer advance. Copy at most `cnt'
 160  * elements from `rb' to `dest'. Returns the actual number of elements copied.
 161  */
 162 size_t ll_ringbuffer_peek(ll_ringbuffer_t *rb, char *dest, size_t cnt)
 163 {
 164     size_t free_cnt;
 165     size_t cnt2;
 166     size_t to_read;
 167     size_t n1, n2;
 168     size_t read_ptr;
 169
 170     free_cnt = ll_ringbuffer_read_space(rb);
 171     if(free_cnt == 0) return 0;
 172
 173     to_read = (cnt > free_cnt) ? free_cnt : cnt;
 174     read_ptr = ATOMIC_LOAD(&rb->read_ptr, almemory_order_relaxed) & rb->size_mask;
 175
 176     cnt2 = read_ptr + to_read;
 177     if(cnt2 > rb->size)
 178     {
 179         n1 = rb->size - read_ptr;
 180         n2 = cnt2 & rb->size_mask;
 181     }
 182     else
 183     {
 184         n1 = to_read;
 185         n2 = 0;
 186     }
 187
 188     memcpy(dest, &rb->buf[read_ptr*rb->elem_size], n1*rb->elem_size);
 189     if(n2)
 190     {
 191         read_ptr += n1;
 192         memcpy(dest + n1*rb->elem_size, &rb->buf[(read_ptr&rb->size_mask)*rb->elem_size],
 193                n2*rb->elem_size);
 194     }
 195     return to_read;
 196 }
 197
 198 /* The copying data writer. Copy at most `cnt' elements to `rb' from `src'.
 199  * Returns the actual number of elements copied. */
 200 size_t ll_ringbuffer_write(ll_ringbuffer_t *rb, const char *src, size_t cnt)
 201 {
 202     size_t write_ptr;
 203     size_t free_cnt;
 204     size_t cnt2;
 205     size_t to_write;
 206     size_t n1, n2;
 207
 208     free_cnt = ll_ringbuffer_write_space(rb);
 209     if(free_cnt == 0) return 0;
 210
 211     to_write = (cnt > free_cnt) ? free_cnt : cnt;
 212     write_ptr = ATOMIC_LOAD(&rb->write_ptr, almemory_order_relaxed) & rb->size_mask;
 213
 214     cnt2 = write_ptr + to_write;
 215     if(cnt2 > rb->size)
 216     {
 217         n1 = rb->size - write_ptr;
 218         n2 = cnt2 & rb->size_mask;
 219     }
 220     else
 221     {
 222         n1 = to_write;
 223         n2 = 0;
 224     }
 225
 226     memcpy(&rb->buf[write_ptr*rb->elem_size], src, n1*rb->elem_size);
 227     write_ptr += n1;
 228     if(n2)
 229     {
 230         memcpy(&rb->buf[(write_ptr&rb->size_mask)*rb->elem_size], src + n1*rb->elem_size,
 231                n2*rb->elem_size);
 232         write_ptr += n2;
 233     }
 234     ATOMIC_STORE(&rb->write_ptr, write_ptr, almemory_order_release);
 235     return to_write;
 236 }
 237
 238 /* Advance the read pointer `cnt' places. */
 239 void ll_ringbuffer_read_advance(ll_ringbuffer_t *rb, size_t cnt)
 240 {
 241     ATOMIC_ADD(&rb->read_ptr, cnt, almemory_order_acq_rel);
 242 }
 243
 244 /* Advance the write pointer `cnt' places. */
 245 void ll_ringbuffer_write_advance(ll_ringbuffer_t *rb, size_t cnt)
 246 {
 247     ATOMIC_ADD(&rb->write_ptr, cnt, almemory_order_acq_rel);
 248 }
 249
 250 /* The non-copying data reader. `vec' is an array of two places. Set the values
 251  * at `vec' to hold the current readable data at `rb'. If the readable data is
 252  * in one segment the second segment has zero length. */
 253 void ll_ringbuffer_get_read_vector(const ll_ringbuffer_t *rb, ll_ringbuffer_data_t * vec)
 254 {
 255     size_t free_cnt;
 256     size_t cnt2;
 257     size_t w, r;
 258
 259     w = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->write_ptr, almemory_order_acquire);
 260     r = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->read_ptr, almemory_order_acquire);
 261     w &= rb->size_mask;
 262     r &= rb->size_mask;
 263     free_cnt = (w-r) & rb->size_mask;
 264
 265     cnt2 = r + free_cnt;
 266     if(cnt2 > rb->size)
 267     {
 268         /* Two part vector: the rest of the buffer after the current write ptr,
 269          * plus some from the start of the buffer. */
 270         vec[0].buf = (char*)&rb->buf[r*rb->elem_size];
 271         vec[0].len = rb->size - r;
 272         vec[1].buf = (char*)rb->buf;
 273         vec[1].len = cnt2 & rb->size_mask;
 274     }
 275     else
 276     {
 277         /* Single part vector: just the rest of the buffer */
 278         vec[0].buf = (char*)&rb->buf[r*rb->elem_size];
 279         vec[0].len = free_cnt;
 280         vec[1].buf = NULL;
 281         vec[1].len = 0;
 282     }
 283 }
 284
 285 /* The non-copying data writer. `vec' is an array of two places. Set the values
 286  * at `vec' to hold the current writeable data at `rb'. If the writeable data
 287  * is in one segment the second segment has zero length. */
 288 void ll_ringbuffer_get_write_vector(const ll_ringbuffer_t *rb, ll_ringbuffer_data_t *vec)
 289 {
 290     size_t free_cnt;
 291     size_t cnt2;
 292     size_t w, r;
 293
 294     w = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->write_ptr, almemory_order_acquire);
 295     r = ATOMIC_LOAD(&CONST_CAST(ll_ringbuffer_t*,rb)->read_ptr, almemory_order_acquire);
 296     w &= rb->size_mask;
 297     r &= rb->size_mask;
 298     free_cnt = (r-w-1) & rb->size_mask;
 299
 300     cnt2 = w + free_cnt;
 301     if(cnt2 > rb->size)
 302     {
 303         /* Two part vector: the rest of the buffer after the current write ptr,
 304          * plus some from the start of the buffer. */
 305         vec[0].buf = (char*)&rb->buf[w*rb->elem_size];
 306         vec[0].len = rb->size - w;
 307         vec[1].buf = (char*)rb->buf;
 308         vec[1].len = cnt2 & rb->size_mask;
 309     }
 310     else
 311     {
 312         vec[0].buf = (char*)&rb->buf[w*rb->elem_size];
 313         vec[0].len = free_cnt;
 314         vec[1].buf = NULL;
 315         vec[1].len = 0;
 316     }
 317 }