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/**************************************************************************//**
* @file
* A ring buffer with multi-threaded synchronization.
*
* License
* -------
*
* Copyright © 2017 AT&T Intellectual Property. All rights reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*****************************************************************************/
#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;
}
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