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libisofs/src/buffer.c

254 lines
6.5 KiB

/*
* Copyright (c) 2007 Vreixo Formoso
*
* This file is part of the libisofs project; you can redistribute it and/or
* modify it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation. See COPYING file for details.
*/
/*
* Synchronized ring buffer, works with a writer thread and a read thread.
*
* TODO things to optimize
* - write/read at the end of buffer requires a second mutex_lock, even if
* there's enought space/data at the beginning
* - pre-buffer for writes < BLOCK_SIZE
*
*/
#include "buffer.h"
#include "error.h"
#include <pthread.h>
#include <string.h>
#define BUFFER_CAPACITY BLOCK_SIZE * BUFFER_SIZE
#ifndef MIN
# define MIN(a, b) (((a) < (b)) ? (a) : (b))
#endif
struct iso_ring_buffer {
uint8_t buf[BLOCK_SIZE * BUFFER_SIZE];
/*
* Number of bytes available.
*/
size_t size;
/* position for reading and writing, offset from buf */
size_t rpos;
size_t wpos;
/* flags to report if read or writer threads ends execution */
unsigned int rend:1;
unsigned int wend:1;
/* just for statistical purposes */
unsigned int times_full;
unsigned int times_empty;
pthread_mutex_t mutex;
pthread_cond_t empty;
pthread_cond_t full;
};
/**
* Create a new buffer.
*
* The created buffer can be freed with free(3)
*
* @return
* 1 success, < 0 error
*/
int iso_ring_buffer_new(IsoRingBuffer **rbuf)
{
IsoRingBuffer *buffer;
if (rbuf == NULL) {
return ISO_NULL_POINTER;
}
buffer = malloc(sizeof(IsoRingBuffer));
if (buffer == NULL) {
return ISO_MEM_ERROR;
}
buffer->size = 0;
buffer->wpos = 0;
buffer->rpos = 0;
buffer->times_full = 0;
buffer->times_empty = 0;
buffer->rend = buffer->wend = 0;
/* init mutex and waiting queues */
pthread_mutex_init(&buffer->mutex, NULL);
pthread_cond_init(&buffer->empty, NULL);
pthread_cond_init(&buffer->full, NULL);
*rbuf = buffer;
return ISO_SUCCESS;
}
void iso_ring_buffer_free(IsoRingBuffer *buf)
{
pthread_mutex_destroy(&buf->mutex);
pthread_cond_destroy(&buf->empty);
pthread_cond_destroy(&buf->full);
free(buf);
}
/**
* Write count bytes into buffer. It blocks until all bytes where written or
* reader close the buffer.
*
* @param buf
* the buffer
* @param data
* pointer to a memory region of at least coun bytes, from which data
* will be read.
* @param
* Number of bytes to write
* @return
* 1 succes, 0 read finished, < 0 error
*/
int iso_ring_buffer_write(IsoRingBuffer *buf, uint8_t *data, size_t count)
{
size_t len;
int bytes_write = 0;
if (buf == NULL || data == NULL) {
return ISO_NULL_POINTER;
}
while (bytes_write < count) {
pthread_mutex_lock(&buf->mutex);
while (buf->size == BUFFER_CAPACITY) {
/*
* Note. There's only a writer, so we have no race conditions.
* Thus, the while(buf->size == BUFFER_CAPACITY) is used here
* only to propertly detect the reader has been cancelled
*/
if (buf->rend) {
/* the read procces has been finished */
pthread_mutex_unlock(&buf->mutex);
return 0;
}
buf->times_full++;
/* wait until space available */
pthread_cond_wait(&buf->full, &buf->mutex);
}
len = MIN(count - bytes_write, BUFFER_CAPACITY - buf->size);
if (buf->wpos + len > BUFFER_CAPACITY) {
len = BUFFER_CAPACITY - buf->wpos;
}
memcpy(buf->buf + buf->wpos, data + bytes_write, len);
buf->wpos = (buf->wpos + len) % (BUFFER_CAPACITY);
bytes_write += len;
buf->size += len;
/* wake up reader */
pthread_cond_signal(&buf->empty);
pthread_mutex_unlock(&buf->mutex);
}
return ISO_SUCCESS;
}
/**
* Read count bytes from the buffer into dest. It blocks until the desired
* bytes has been read. If the writer finishes before outputting enought
* bytes, 0 (EOF) is returned, the number of bytes already read remains
* unknown.
*
* @return
* 1 success, 0 EOF, < 0 error
*/
int iso_ring_buffer_read(IsoRingBuffer *buf, uint8_t *dest, size_t count)
{
size_t len;
int bytes_read = 0;
if (buf == NULL || dest == NULL) {
return ISO_NULL_POINTER;
}
while (bytes_read < count) {
pthread_mutex_lock(&buf->mutex);
while (buf->size == 0) {
/*
* Note. There's only a reader, so we have no race conditions.
* Thus, the while(buf->size == 0) is used here just to ensure
* a reader detects the EOF propertly if the writer has been
* canceled while the reader was waiting
*/
if (buf->wend) {
/* the writer procces has been finished */
pthread_mutex_unlock(&buf->mutex);
return 0; /* EOF */
}
buf->times_empty++;
/* wait until data available */
pthread_cond_wait(&buf->empty, &buf->mutex);
}
len = MIN(count - bytes_read, buf->size);
if (buf->rpos + len > BUFFER_CAPACITY) {
len = BUFFER_CAPACITY - buf->rpos;
}
memcpy(dest + bytes_read, buf->buf + buf->rpos, len);
buf->rpos = (buf->rpos + len) % (BUFFER_CAPACITY);
bytes_read += len;
buf->size -= len;
/* wake up the writer */
pthread_cond_signal(&buf->full);
pthread_mutex_unlock(&buf->mutex);
}
return ISO_SUCCESS;
}
void iso_ring_buffer_writer_close(IsoRingBuffer *buf)
{
pthread_mutex_lock(&buf->mutex);
buf->wend = 1;
/* ensure no reader is waiting */
pthread_cond_signal(&buf->empty);
pthread_mutex_unlock(&buf->mutex);
}
void iso_ring_buffer_reader_close(IsoRingBuffer *buf)
{
pthread_mutex_lock(&buf->mutex);
buf->rend = 1;
/* ensure no writer is waiting */
pthread_cond_signal(&buf->full);
pthread_mutex_unlock(&buf->mutex);
}
/**
* Get the times the buffer was full.
*/
unsigned int iso_ring_buffer_get_times_full(IsoRingBuffer *buf)
{
return buf->times_full;
}
/**
* Get the times the buffer was empty.
*/
unsigned int iso_ring_buffer_get_times_empty(IsoRingBuffer *buf)
{
return buf->times_empty;
}