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