Alc/ringbuffer.cpp

   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 #include <limits.h>
  26
  27 #include "ringbuffer.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     std::atomic<size_t> write_ptr;
  40     std::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 ll_ringbuffer_t *ll_ringbuffer_create(size_t sz, size_t elem_sz, int limit_writes)
  49 {
  50     ll_ringbuffer_t *rb;
  51     size_t power_of_two = 0;
  52
  53     if(sz > 0)
  54     {
  55         power_of_two = sz;
  56         power_of_two |= power_of_two>>1;
  57         power_of_two |= power_of_two>>2;
  58         power_of_two |= power_of_two>>4;
  59         power_of_two |= power_of_two>>8;
  60         power_of_two |= power_of_two>>16;
  61 #if SIZE_MAX > UINT_MAX
  62         power_of_two |= power_of_two>>32;
  63 #endif
  64     }
  65     power_of_two++;
  66     if(power_of_two < sz) return NULL;
  67
  68     rb = static_cast<ll_ringbuffer_t*>(al_malloc(16, sizeof(*rb) + power_of_two*elem_sz));
  69     if(!rb) return NULL;
  70
  71     ATOMIC_INIT(&rb->write_ptr, static_cast<size_t>(0));
  72     ATOMIC_INIT(&rb->read_ptr, static_cast<size_t>(0));
  73     rb->size = limit_writes ? sz : power_of_two;
  74     rb->size_mask = power_of_two - 1;
  75     rb->elem_size = elem_sz;
  76     return rb;
  77 }
  78
  79 void ll_ringbuffer_free(ll_ringbuffer_t *rb)
  80 {
  81     al_free(rb);
  82 }
  83
  84 void ll_ringbuffer_reset(ll_ringbuffer_t *rb)
  85 {
  86     rb->write_ptr.store(0, std::memory_order_release);
  87     rb->read_ptr.store(0, std::memory_order_release);
  88     memset(rb->buf, 0, (rb->size_mask+1)*rb->elem_size);
  89 }
  90
  91
  92 size_t ll_ringbuffer_read_space(const ll_ringbuffer_t *rb)
  93 {
  94     size_t w = rb->write_ptr.load(std::memory_order_acquire);
  95     size_t r = rb->read_ptr.load(std::memory_order_acquire);
  96     return (w-r) & rb->size_mask;
  97 }
  98
  99 size_t ll_ringbuffer_write_space(const ll_ringbuffer_t *rb)
 100 {
 101     size_t w = rb->write_ptr.load(std::memory_order_acquire);
 102     size_t r = rb->read_ptr.load(std::memory_order_acquire);
 103     w = (r-w-1) & rb->size_mask;
 104     return (w > rb->size) ? rb->size : w;
 105 }
 106
 107
 108 size_t ll_ringbuffer_read(ll_ringbuffer_t *rb, char *dest, size_t cnt)
 109 {
 110     size_t read_ptr;
 111     size_t free_cnt;
 112     size_t cnt2;
 113     size_t to_read;
 114     size_t n1, n2;
 115
 116     free_cnt = ll_ringbuffer_read_space(rb);
 117     if(free_cnt == 0) return 0;
 118
 119     to_read = (cnt > free_cnt) ? free_cnt : cnt;
 120     read_ptr = rb->read_ptr.load(std::memory_order_relaxed) & rb->size_mask;
 121
 122     cnt2 = read_ptr + to_read;
 123     if(cnt2 > rb->size_mask+1)
 124     {
 125         n1 = rb->size_mask+1 - read_ptr;
 126         n2 = cnt2 & rb->size_mask;
 127     }
 128     else
 129     {
 130         n1 = to_read;
 131         n2 = 0;
 132     }
 133
 134     memcpy(dest, &rb->buf[read_ptr*rb->elem_size], n1*rb->elem_size);
 135     read_ptr += n1;
 136     if(n2)
 137     {
 138         memcpy(dest + n1*rb->elem_size, &rb->buf[(read_ptr&rb->size_mask)*rb->elem_size],
 139                n2*rb->elem_size);
 140         read_ptr += n2;
 141     }
 142     rb->read_ptr.store(read_ptr, std::memory_order_release);
 143     return to_read;
 144 }
 145
 146 size_t ll_ringbuffer_peek(ll_ringbuffer_t *rb, char *dest, size_t cnt)
 147 {
 148     size_t free_cnt;
 149     size_t cnt2;
 150     size_t to_read;
 151     size_t n1, n2;
 152     size_t read_ptr;
 153
 154     free_cnt = ll_ringbuffer_read_space(rb);
 155     if(free_cnt == 0) return 0;
 156
 157     to_read = (cnt > free_cnt) ? free_cnt : cnt;
 158     read_ptr = rb->read_ptr.load(std::memory_order_relaxed) & rb->size_mask;
 159
 160     cnt2 = read_ptr + to_read;
 161     if(cnt2 > rb->size_mask+1)
 162     {
 163         n1 = rb->size_mask+1 - read_ptr;
 164         n2 = cnt2 & rb->size_mask;
 165     }
 166     else
 167     {
 168         n1 = to_read;
 169         n2 = 0;
 170     }
 171
 172     memcpy(dest, &rb->buf[read_ptr*rb->elem_size], n1*rb->elem_size);
 173     if(n2)
 174     {
 175         read_ptr += n1;
 176         memcpy(dest + n1*rb->elem_size, &rb->buf[(read_ptr&rb->size_mask)*rb->elem_size],
 177                n2*rb->elem_size);
 178     }
 179     return to_read;
 180 }
 181
 182 size_t ll_ringbuffer_write(ll_ringbuffer_t *rb, const char *src, size_t cnt)
 183 {
 184     size_t write_ptr;
 185     size_t free_cnt;
 186     size_t cnt2;
 187     size_t to_write;
 188     size_t n1, n2;
 189
 190     free_cnt = ll_ringbuffer_write_space(rb);
 191     if(free_cnt == 0) return 0;
 192
 193     to_write = (cnt > free_cnt) ? free_cnt : cnt;
 194     write_ptr = rb->write_ptr.load(std::memory_order_relaxed) & rb->size_mask;
 195
 196     cnt2 = write_ptr + to_write;
 197     if(cnt2 > rb->size_mask+1)
 198     {
 199         n1 = rb->size_mask+1 - write_ptr;
 200         n2 = cnt2 & rb->size_mask;
 201     }
 202     else
 203     {
 204         n1 = to_write;
 205         n2 = 0;
 206     }
 207
 208     memcpy(&rb->buf[write_ptr*rb->elem_size], src, n1*rb->elem_size);
 209     write_ptr += n1;
 210     if(n2)
 211     {
 212         memcpy(&rb->buf[(write_ptr&rb->size_mask)*rb->elem_size], src + n1*rb->elem_size,
 213                n2*rb->elem_size);
 214         write_ptr += n2;
 215     }
 216     rb->write_ptr.store(write_ptr, std::memory_order_release);
 217     return to_write;
 218 }
 219
 220
 221 void ll_ringbuffer_read_advance(ll_ringbuffer_t *rb, size_t cnt)
 222 {
 223     rb->read_ptr.fetch_add(cnt, std::memory_order_acq_rel);
 224 }
 225
 226 void ll_ringbuffer_write_advance(ll_ringbuffer_t *rb, size_t cnt)
 227 {
 228     rb->write_ptr.fetch_add(cnt, std::memory_order_acq_rel);
 229 }
 230
 231
 232 void ll_ringbuffer_get_read_vector(const ll_ringbuffer_t *rb, ll_ringbuffer_data_t vec[2])
 233 {
 234     size_t free_cnt;
 235     size_t cnt2;
 236
 237     size_t w = rb->write_ptr.load(std::memory_order_acquire);
 238     size_t r = rb->read_ptr.load(std::memory_order_acquire);
 239     w &= rb->size_mask;
 240     r &= rb->size_mask;
 241     free_cnt = (w-r) & rb->size_mask;
 242
 243     cnt2 = r + free_cnt;
 244     if(cnt2 > rb->size_mask+1)
 245     {
 246         /* Two part vector: the rest of the buffer after the current write ptr,
 247          * plus some from the start of the buffer. */
 248         vec[0].buf = const_cast<char*>(&rb->buf[r*rb->elem_size]);
 249         vec[0].len = rb->size_mask+1 - r;
 250         vec[1].buf = const_cast<char*>(rb->buf);
 251         vec[1].len = cnt2 & rb->size_mask;
 252     }
 253     else
 254     {
 255         /* Single part vector: just the rest of the buffer */
 256         vec[0].buf = const_cast<char*>(&rb->buf[r*rb->elem_size]);
 257         vec[0].len = free_cnt;
 258         vec[1].buf = nullptr;
 259         vec[1].len = 0;
 260     }
 261 }
 262
 263 void ll_ringbuffer_get_write_vector(const ll_ringbuffer_t *rb, ll_ringbuffer_data_t vec[2])
 264 {
 265     size_t free_cnt;
 266     size_t cnt2;
 267
 268     size_t w = rb->write_ptr.load(std::memory_order_acquire);
 269     size_t r = rb->read_ptr.load(std::memory_order_acquire);
 270     w &= rb->size_mask;
 271     r &= rb->size_mask;
 272     free_cnt = (r-w-1) & rb->size_mask;
 273     if(free_cnt > rb->size) free_cnt = rb->size;
 274
 275     cnt2 = w + free_cnt;
 276     if(cnt2 > rb->size_mask+1)
 277     {
 278         /* Two part vector: the rest of the buffer after the current write ptr,
 279          * plus some from the start of the buffer. */
 280         vec[0].buf = const_cast<char*>(&rb->buf[w*rb->elem_size]);
 281         vec[0].len = rb->size_mask+1 - w;
 282         vec[1].buf = const_cast<char*>(rb->buf);
 283         vec[1].len = cnt2 & rb->size_mask;
 284     }
 285     else
 286     {
 287         vec[0].buf = const_cast<char*>(&rb->buf[w*rb->elem_size]);
 288         vec[0].len = free_cnt;
 289         vec[1].buf = nullptr;
 290         vec[1].len = 0;
 291     }
 292 }