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 #if HAVE_CONFIG_H
  29 #       include "config.h"
  30 #endif /* HAVE_CONFIG_H */
  31
  32 #include "utils/channel.h"
  33
  34 #include <assert.h>
  35 #include <errno.h>
  36
  37 #include <stdbool.h>
  38 #include <stdlib.h>
  39 #include <string.h>
  40
  41 #include <time.h>
  42
  43 #include <pthread.h>
  44
  45 /*
  46  * private data types
  47  */
  48
  49 struct sdb_channel {
  50         pthread_mutex_t lock;
  51
  52         /* signaling for select() operation */
  53         pthread_cond_t cond;
  54
  55         /* maybe TODO: add support for 'nil' values using a boolean area */
  56
  57         void  *data;
  58         size_t data_len;
  59         size_t elem_size;
  60
  61         size_t head;
  62         size_t tail;
  63         bool  full;
  64
  65         bool shutdown;
  66 };
  67
  68 /*
  69  * private helper functions
  70  */
  71
  72 #define NEXT_WRITE(chan) (((chan)->tail + 1) % (chan)->data_len)
  73 #define NEXT_READ(chan) (((chan)->head + 1) % (chan)->data_len)
  74
  75 #define ELEM(chan, i) \
  76         (void *)((char *)(chan)->data + (i) * (chan)->elem_size)
  77 #define TAIL(chan) ELEM(chan, (chan)->tail)
  78 #define HEAD(chan) ELEM(chan, (chan)->head)
  79
  80 /* Insert a new element at the end; chan->lock must be held.
  81  * Returns 0 if data has been written or if data may be written
  82  * if 'data' is NULL. */
  83 static int
  84 channel_write(sdb_channel_t *chan, const void *data)
  85 {
  86         assert(chan);
  87
  88         if (chan->full || chan->shutdown)
  89                 return -1;
  90         else if (! data)
  91                 return 0;
  92
  93         memcpy(TAIL(chan), data, chan->elem_size);
  94         chan->tail = NEXT_WRITE(chan);
  95
  96         chan->full = chan->tail == chan->head;
  97         pthread_cond_broadcast(&chan->cond);
  98         return 0;
  99 } /* channel_write */
 100
 101 /* Retrieve the first element; chan->lock must be held.
 102  * Returns 0 if data has been read or if data is available
 103  * if 'data' is NULL. */
 104 static int
 105 channel_read(sdb_channel_t *chan, void *data)
 106 {
 107         assert(chan);
 108
 109         if ((chan->head == chan->tail) && (! chan->full))
 110                 return -1;
 111         else if (! data)
 112                 return 0;
 113
 114         memcpy(data, HEAD(chan), chan->elem_size);
 115         chan->head = NEXT_READ(chan);
 116
 117         chan->full = 0;
 118         pthread_cond_broadcast(&chan->cond);
 119         return 0;
 120 } /* channel_read */
 121
 122 /*
 123  * public API
 124  */
 125
 126 sdb_channel_t *
 127 sdb_channel_create(size_t size, size_t elem_size)
 128 {
 129         sdb_channel_t *chan;
 130
 131         if (! elem_size)
 132                 return NULL;
 133         if (! size)
 134                 size = 1;
 135
 136         chan = calloc(1, sizeof(*chan));
 137         if (! chan)
 138                 return NULL;
 139
 140         chan->data = calloc(size, elem_size);
 141         if (! chan->data) {
 142                 sdb_channel_destroy(chan);
 143                 return NULL;
 144         }
 145
 146         chan->data_len = size;
 147         chan->elem_size = elem_size;
 148
 149         pthread_mutex_init(&chan->lock, /* attr = */ NULL);
 150         pthread_cond_init(&chan->cond, /* attr = */ NULL);
 151
 152         chan->head = chan->tail = 0;
 153         return chan;
 154 } /* sdb_channel_create */
 155
 156 void
 157 sdb_channel_destroy(sdb_channel_t *chan)
 158 {
 159         if (! chan)
 160                 return;
 161
 162         pthread_mutex_lock(&chan->lock);
 163         free(chan->data);
 164         chan->data = NULL;
 165         chan->data_len = 0;
 166
 167         pthread_cond_destroy(&chan->cond);
 168
 169         pthread_mutex_unlock(&chan->lock);
 170         pthread_mutex_destroy(&chan->lock);
 171         free(chan);
 172 } /* sdb_channel_destroy */
 173
 174 int
 175 sdb_channel_select(sdb_channel_t *chan, int *wantread, void *read_data,
 176                 int *wantwrite, void *write_data, const struct timespec *timeout)
 177 {
 178         int status = 0;
 179
 180         if (! chan) {
 181                 errno = EINVAL;
 182                 return -1;
 183         }
 184
 185         if ((! wantread) && (! read_data) && (! wantwrite) && (! write_data)) {
 186                 errno = EINVAL;
 187                 return -1;
 188         }
 189
 190         pthread_mutex_lock(&chan->lock);
 191         while (! status) {
 192                 int read_status, write_status;
 193
 194                 read_status = channel_read(chan, read_data);
 195                 write_status = channel_write(chan, write_data);
 196
 197                 if ((! read_status) || (! write_status)) {
 198                         if (wantread)
 199                                 *wantread = read_status == 0;
 200                         if (wantwrite)
 201                                 *wantwrite = write_status == 0;
 202
 203                         if (((wantread || read_data) && (! read_status))
 204                                         || ((wantwrite || write_data) && (! write_status)))
 205                                 break;
 206                 }
 207
 208                 if (chan->shutdown) {
 209                         if (read_status)
 210                                 status = EBADF;
 211                         break;
 212                 }
 213
 214                 if (timeout) {
 215                         struct timespec abstime;
 216
 217                         if (clock_gettime(CLOCK_REALTIME, &abstime)) {
 218                                 pthread_mutex_unlock(&chan->lock);
 219                                 return -1;
 220                         }
 221
 222                         abstime.tv_sec += timeout->tv_sec;
 223                         abstime.tv_nsec += timeout->tv_nsec;
 224
 225                         if (abstime.tv_nsec > 1000000000) {
 226                                 abstime.tv_nsec -= 1000000000;
 227                                 abstime.tv_sec += 1;
 228                         }
 229
 230                         status = pthread_cond_timedwait(&chan->cond, &chan->lock,
 231                                         &abstime);
 232                 }
 233                 else
 234                         status = pthread_cond_wait(&chan->cond, &chan->lock);
 235         }
 236         pthread_mutex_unlock(&chan->lock);
 237
 238         if (status) {
 239                 errno = status;
 240                 return -1;
 241         }
 242         return 0;
 243 } /* sdb_channel_select */
 244
 245 int
 246 sdb_channel_write(sdb_channel_t *chan, const void *data)
 247 {
 248         int status;
 249
 250         if ((! chan) || (! data))
 251                 return -1;
 252
 253         pthread_mutex_lock(&chan->lock);
 254         status = channel_write(chan, data);
 255         pthread_mutex_unlock(&chan->lock);
 256         return status;
 257 } /* sdb_channel_write */
 258
 259 int
 260 sdb_channel_read(sdb_channel_t *chan, void *data)
 261 {
 262         int status;
 263
 264         if ((! chan) || (! data))
 265                 return -1;
 266
 267         pthread_mutex_lock(&chan->lock);
 268         status = channel_read(chan, data);
 269         pthread_mutex_unlock(&chan->lock);
 270         return status;
 271 } /* sdb_channel_read */
 272
 273 int
 274 sdb_channel_shutdown(sdb_channel_t *chan)
 275 {
 276         if (! chan)
 277                 return -1;
 278         chan->shutdown = 1;
 279         return 0;
 280 } /* sdb_channel_shutdown */
 281
 282 /* vim: set tw=78 sw=4 ts=4 noexpandtab : */
 283