research.m1stereo.tv/gitweb/ - melted/blob - src/modules/jackrack/lock_free_fifo.c

   1 /*
   2  * JACK Rack
   3  *
   4  * Original:
   5  * Copyright (C) Robert Ham 2002, 2003 (node@users.sourceforge.net)
   6  *
   7  * Modification for MLT:
   8  * Copyright (C) 2004 Ushodaya Enterprises Limited
   9  * Author: Dan Dennedy <dan@dennedy.org>
  10  *
  11  * This program is free software; you can redistribute it and/or modify
  12  * it under the terms of the GNU General Public License as published by
  13  * the Free Software Foundation; either version 2 of the License, or
  14  * (at your option) any later version.
  15  *
  16  * This program is distributed in the hope that it will be useful,
  17  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  18  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  19  * GNU General Public License for more details.
  20  *
  21  * You should have received a copy of the GNU General Public License
  22  * along with this program; if not, write to the Free Software
  23  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  24  */
  25
  26 #include <stdio.h>
  27 #include <stdlib.h>
  28 #include <string.h>
  29
  30 #include <glib.h>
  31
  32 #include "lock_free_fifo.h"
  33
  34 /** initialise a lock free fifo */
  35
  36 void
  37 lff_init (lff_t * lff, unsigned int size, size_t object_size)
  38 {
  39   lff->size = size;
  40   lff->object_size = object_size;
  41   lff->read_index = 0;
  42   lff->write_index = 0;
  43   lff->data = g_malloc (object_size * size);
  44 }
  45
  46 lff_t *
  47 lff_new (unsigned int size, size_t object_size)
  48 {
  49   lff_t * lff;
  50
  51   lff = g_malloc (sizeof (lff_t));
  52
  53   lff_init (lff, size, object_size);
  54
  55   return lff;
  56 }
  57
  58 void
  59 lff_free (lff_t * lff)
  60 {
  61   g_free (lff->data);
  62 }
  63
  64 void
  65 lff_destroy (lff_t * lff)
  66 {
  67   lff_free (lff);
  68   g_free (lff);
  69 }
  70
  71 /** read an element from the fifo into data.
  72 returns 0 on success, non-zero if there were no elements to read */
  73 int lff_read (lff_t * lff, void * data) {
  74   if (lff->read_index == lff->write_index) {
  75     return -1;
  76   } else {
  77     memcpy (data, ((char *)lff->data) + (lff->read_index * lff->object_size),
  78             lff->object_size);
  79     lff->read_index++;
  80     if (lff->read_index >= lff->size) {
  81       lff->read_index = 0;
  82     }
  83     return 0;
  84   }
  85 }
  86
  87 /** write an element from data to the fifo.
  88 returns 0 on success, non-zero if there was no space */
  89 int lff_write (lff_t * lff, void * data) {
  90   static unsigned int ri;
  91
  92   /* got to read read_index only once for safety */
  93   ri = lff->read_index;
  94
  95   /* lots of logic for when we're allowed to write to the fifo which basically
  96      boils down to "don't write if we're one element behind the read index" */
  97   if ((ri > lff->write_index && ri - lff->write_index > 1) ||
  98       (lff->write_index >= ri && lff->write_index != lff->size - 1) ||
  99       (lff->write_index >= ri && lff->write_index == lff->size - 1 && ri != 0)) {
 100
 101 /*  if ((ri > lff->write_index && ri - lff->write_index > 1) ||
 102       (lff->write_index >= ri && (lff->write_index != lff->size - 1 || ri != 0))) { */
 103
 104     memcpy (((char *)lff->data) + (lff->write_index * lff->object_size),
 105             data, lff->object_size);
 106
 107     /* FIXME: is this safe? */
 108     lff->write_index++;
 109     if (lff->write_index >= lff->size) {
 110       lff->write_index = 0;
 111     }
 112
 113     return 0;
 114   } else {
 115     return -1;
 116   }
 117 }