summaryrefslogtreecommitdiffstats
path: root/VES5.0/evel/evel-library/code/evel_library/ring_buffer.c
blob: 3795ed365cf4b44bd5e2308501d5963f36f7ac9e (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
/**************************************************************************//**
 * @file
 * A ring buffer with multi-threaded synchronization.
 *
 * License
 * -------
 *
 * Copyright(c) <2016>, AT&T Intellectual Property.  All other rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:  This product includes
 *    software developed by the AT&T.
 * 4. Neither the name of AT&T nor the names of its contributors may be used to
 *    endorse or promote products derived from this software without specific
 *    prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY AT&T INTELLECTUAL PROPERTY ''AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL AT&T INTELLECTUAL PROPERTY BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *****************************************************************************/

#include <assert.h>
#include <malloc.h>

#include "ring_buffer.h"
#include "evel.h"

/**************************************************************************//**
 * Ring buffer initialization.
 *
 * Initialize the buffer supplied to the specified size.
 *
 * @param   buffer  Pointer to the ring-buffer to be initialized.
 * @param   size    How many elements to be stored in the ring-buffer.
 *
 * @returns Nothing
******************************************************************************/
void ring_buffer_initialize(ring_buffer * buffer, int size)
{
  int pthread_rc = 0;

  EVEL_ENTER();

  /***************************************************************************/
  /* Check assumptions.                                                      */
  /***************************************************************************/
  assert(buffer != NULL);
  assert(size > 0);

  /***************************************************************************/
  /* Initialize the synchronization objects.                                 */
  /***************************************************************************/
  pthread_rc = pthread_mutex_init(&buffer->ring_mutex, NULL);
  assert(pthread_rc == 0);
  pthread_rc = pthread_cond_init(&buffer->ring_cv, NULL);
  assert(pthread_rc == 0);

  /***************************************************************************/
  /* Allocate the ring buffer itself.                                        */
  /***************************************************************************/
  buffer->ring = malloc(size * sizeof(void *));
  assert(buffer->ring != NULL);

  /***************************************************************************/
  /* Initialize the ring as empty.                                           */
  /***************************************************************************/
  buffer->next_write = 0;
  buffer->next_read = 0;
  buffer->size = size;

  EVEL_EXIT();
}

/**************************************************************************//**
 * Read an element from a ring_buffer.
 *
 * Reads an element from the ring_buffer, advancing the next-read position.
 * Operation is synchronized and therefore MT-safe.  Blocks if no data is
 * available.
 *
 * @param   buffer  Pointer to the ring-buffer to be read.
 *
 * @returns Pointer to the element read from the buffer.
******************************************************************************/
void * ring_buffer_read(ring_buffer * buffer)
{
  void *msg = NULL;
  EVEL_DEBUG("RBR: Ring buffer read");

  pthread_mutex_lock(&buffer->ring_mutex);
  while (1)
  {
    EVEL_DEBUG("RBR: got lock. NR=%d NW=%d",
               buffer->next_read,
               buffer->next_write);
    if(buffer->next_read != buffer->next_write)
    {
      EVEL_DEBUG("RBR: buffer has item available");
      msg = (buffer->ring)[buffer->next_read];
      buffer->ring[buffer->next_read] = NULL;
      buffer->next_read = (buffer->next_read + 1) % buffer->size;
      EVEL_DEBUG("RBR: next read location is %d", buffer->next_read);
      pthread_mutex_unlock(&buffer->ring_mutex);
      break;
    }
    else
    {
      EVEL_DEBUG("RBR: Waiting for condition variable");
      pthread_cond_wait(&buffer->ring_cv, &buffer->ring_mutex);
      EVEL_DEBUG("RBR: Condition variable wait completed");
    }
  }
  EVEL_DEBUG("RBR: Ring buffer read returning data at %lp", msg);
  return msg;
}

/**************************************************************************//**
 * Write an element into a ring_buffer.
 *
 * Writes an element into the ring_buffer, advancing the next-write position.
 * Operation is synchronized and therefore MT-safe.  Fails if the buffer is
 * full without blocking.
 *
 * @param   buffer  Pointer to the ring-buffer to be written.
 * @param   msg     Pointer to data to be stored in the ring_buffer.
 *
 * @returns Number of items written.
 * @retval  1       The data was written successfully.
 * @retval  0       The ring_buffer was full so no data written.
******************************************************************************/
int ring_buffer_write(ring_buffer * buffer, void * msg)
{
  int item_count = 0;
  int items_written = 0;
  EVEL_DEBUG("RBW: Ring Buffer Write message at %lp", msg);

  pthread_mutex_lock(&buffer->ring_mutex);
  EVEL_DEBUG("RBW: got lock. NR=%d NW=%d SZ=%d",
             buffer->next_read,
             buffer->next_write,
             buffer->size);

  item_count = (buffer->next_write - buffer->next_read) % buffer->size;
  if (item_count < 0)
  {
    item_count += buffer->size;
  }
  if (item_count < buffer->size - 1)
  {
    EVEL_DEBUG("RBW: %d items in buffer", item_count);
    buffer->ring[buffer->next_write] = msg;
    buffer->next_write = (buffer->next_write + 1) % buffer->size;
    EVEL_DEBUG("RBW: next write location is %d", buffer->next_write);
    items_written = 1;
  }
  else
  {
    EVEL_ERROR("RBW: ring buffer full - unable to write event");
  }

  pthread_mutex_unlock(&buffer->ring_mutex);
  EVEL_DEBUG("RBW: released lock");
  pthread_cond_signal(&buffer->ring_cv);

  return items_written;
}

/**************************************************************************//**
 * Tests whether there is data in the ring_buffer.
 *
 * Tests whether there is currently data in the ring_buffer without blocking.
 *
 * @param   buffer  Pointer to the ring-buffer to be tested.
 *
 * @returns Whether there is data in the ring_buffer.
 * @retval  0       There isn't any data in the ring_buffer.
 * @retval  1       There is data in the ring_buffer.
******************************************************************************/
int ring_buffer_is_empty(ring_buffer * buffer)
{
  int is_empty = 0;
  EVEL_DEBUG("RBE: Ring empty check");

  pthread_mutex_lock(&buffer->ring_mutex);
  is_empty = (buffer->next_read == buffer->next_write);
  pthread_mutex_unlock(&buffer->ring_mutex);

  EVEL_DEBUG("RBE: Ring state= %d", is_empty);
  return is_empty;
}