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

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