src/utils/channel.c

   1 /*
   2  * SysDB - src/utils/channel.c
   3  * Copyright (C) 2013 Sebastian 'tokkee' Harl <sh@tokkee.org>
   4  * All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  * 1. Redistributions of source code must retain the above copyright
  10  *    notice, this list of conditions and the following disclaimer.
  11  * 2. Redistributions in binary form must reproduce the above copyright
  12  *    notice, this list of conditions and the following disclaimer in the
  13  *    documentation and/or other materials provided with the distribution.
  14  *
  15  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  16  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
  17  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  18  * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR
  19  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  20  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  21  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
  22  * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
  23  * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
  24  * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
  25  * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  26  */
  27
  28 #include "utils/channel.h"
  29
  30 #include <assert.h>
  31
  32 #include <errno.h>
  33
  34 #include <stdlib.h>
  35 #include <string.h>
  36
  37 #include <time.h>
  38
  39 #include <pthread.h>
  40
  41 /*
  42  * private data types
  43  */
  44
  45 struct sdb_channel {
  46         pthread_mutex_t lock;
  47
  48         /* signaling for select() operation */
  49         pthread_cond_t cond;
  50
  51         /* maybe TODO: add support for 'nil' values using a boolean area */
  52
  53         void  *data;
  54         size_t data_len;
  55         size_t elem_size;
  56
  57         size_t head;
  58         size_t tail;
  59         _Bool full;
  60 };
  61
  62 /*
  63  * private helper functions
  64  */
  65
  66 #define NEXT_WRITE(chan) (((chan)->tail + 1) % (chan)->data_len)
  67 #define NEXT_READ(chan) (((chan)->head + 1) % (chan)->data_len)
  68
  69 #define ELEM(chan, i) \
  70         (void *)((char *)(chan)->data + (i) * (chan)->elem_size)
  71 #define TAIL(chan) ELEM(chan, (chan)->tail)
  72 #define HEAD(chan) ELEM(chan, (chan)->head)
  73
  74 /* Insert a new element at the end; chan->lock must be held.
  75  * Returns 0 if data has been written or if data may be written
  76  * if 'data' is NULL. */
  77 static int
  78 channel_write(sdb_channel_t *chan, const void *data)
  79 {
  80         assert(chan);
  81
  82         if (chan->full)
  83                 return -1;
  84         else if (! data)
  85                 return 0;
  86
  87         memcpy(TAIL(chan), data, chan->elem_size);
  88         chan->tail = NEXT_WRITE(chan);
  89
  90         chan->full = chan->tail == chan->head;
  91         pthread_cond_broadcast(&chan->cond);
  92         return 0;
  93 } /* channel_write */
  94
  95 /* Retrieve the first element; chan->lock must be held.
  96  * Returns 0 if data has been read or if data is available
  97  * if 'data' is NULL. */
  98 static int
  99 channel_read(sdb_channel_t *chan, void *data)
 100 {
 101         assert(chan);
 102
 103         if ((chan->head == chan->tail) && (! chan->full))
 104                 return -1;
 105         else if (! data)
 106                 return 0;
 107
 108         memcpy(data, HEAD(chan), chan->elem_size);
 109         chan->head = NEXT_READ(chan);
 110
 111         chan->full = 0;
 112         pthread_cond_broadcast(&chan->cond);
 113         return 0;
 114 } /* channel_read */
 115
 116 /*
 117  * public API
 118  */
 119
 120 sdb_channel_t *
 121 sdb_channel_create(size_t size, size_t elem_size)
 122 {
 123         sdb_channel_t *chan;
 124
 125         if (! elem_size)
 126                 return NULL;
 127         if (! size)
 128                 size = 1;
 129
 130         chan = calloc(1, sizeof(*chan));
 131         if (! chan)
 132                 return NULL;
 133
 134         chan->data = calloc(size, elem_size);
 135         if (! chan->data) {
 136                 sdb_channel_destroy(chan);
 137                 return NULL;
 138         }
 139
 140         chan->data_len = size;
 141         chan->elem_size = elem_size;
 142
 143         pthread_mutex_init(&chan->lock, /* attr = */ NULL);
 144         pthread_cond_init(&chan->cond, /* attr = */ NULL);
 145
 146         chan->head = chan->tail = 0;
 147         return chan;
 148 } /* sdb_channel_create */
 149
 150 void
 151 sdb_channel_destroy(sdb_channel_t *chan)
 152 {
 153         if (! chan)
 154                 return;
 155
 156         pthread_mutex_lock(&chan->lock);
 157         free(chan->data);
 158         chan->data = NULL;
 159         chan->data_len = 0;
 160
 161         pthread_cond_destroy(&chan->cond);
 162
 163         pthread_mutex_unlock(&chan->lock);
 164         pthread_mutex_destroy(&chan->lock);
 165         free(chan);
 166 } /* sdb_channel_destroy */
 167
 168 int
 169 sdb_channel_select(sdb_channel_t *chan, int *wantread, void *read_data,
 170                 int *wantwrite, void *write_data, const struct timespec *timeout)
 171 {
 172         int status = 0;
 173
 174         if (! chan) {
 175                 errno = EINVAL;
 176                 return -1;
 177         }
 178
 179         if ((! wantread) && (! read_data) && (! wantwrite) && (! write_data)) {
 180                 errno = EINVAL;
 181                 return -1;
 182         }
 183
 184         pthread_mutex_lock(&chan->lock);
 185         while (! status) {
 186                 int read_status, write_status;
 187
 188                 read_status = channel_read(chan, read_data);
 189                 write_status = channel_write(chan, write_data);
 190
 191                 if ((! read_status) || (! write_status)) {
 192                         if (wantread)
 193                                 *wantread = read_status == 0;
 194                         if (wantwrite)
 195                                 *wantwrite = write_status == 0;
 196
 197                         if (((wantread || read_data) && (! read_status))
 198                                         || ((wantwrite || write_data) && (! write_status)))
 199                                 break;
 200                 }
 201
 202                 if (timeout) {
 203                         struct timespec abstime;
 204
 205                         if (clock_gettime(CLOCK_REALTIME, &abstime)) {
 206                                 pthread_mutex_unlock(&chan->lock);
 207                                 return -1;
 208                         }
 209
 210                         abstime.tv_sec += timeout->tv_sec;
 211                         abstime.tv_nsec += timeout->tv_nsec;
 212
 213                         if (abstime.tv_nsec > 1000000000) {
 214                                 abstime.tv_nsec -= 1000000000;
 215                                 abstime.tv_sec += 1;
 216                         }
 217
 218                         status = pthread_cond_timedwait(&chan->cond, &chan->lock,
 219                                         &abstime);
 220                 }
 221                 else
 222                         status = pthread_cond_wait(&chan->cond, &chan->lock);
 223         }
 224         pthread_mutex_unlock(&chan->lock);
 225
 226         if (status) {
 227                 errno = status;
 228                 return -1;
 229         }
 230         return 0;
 231 } /* sdb_channel_select */
 232
 233 int
 234 sdb_channel_write(sdb_channel_t *chan, const void *data)
 235 {
 236         int status;
 237
 238         if ((! chan) || (! data))
 239                 return -1;
 240
 241         pthread_mutex_lock(&chan->lock);
 242         status = channel_write(chan, data);
 243         pthread_mutex_unlock(&chan->lock);
 244         return status;
 245 } /* sdb_channel_write */
 246
 247 int
 248 sdb_channel_read(sdb_channel_t *chan, void *data)
 249 {
 250         int status;
 251
 252         if ((! chan) || (! data))
 253                 return -1;
 254
 255         pthread_mutex_lock(&chan->lock);
 256         status = channel_read(chan, data);
 257         pthread_mutex_unlock(&chan->lock);
 258         return status;
 259 } /* sdb_channel_read */
 260
 261 /* vim: set tw=78 sw=4 ts=4 noexpandtab : */
 262