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/*
* File : lf_ring_buffer.c
* Author : Jérémy Zurcher <jeremy@asynk.ch>
* Date : 05/01/010
* License :
*
* Permission is hereby granted, free of charge, to any person obtaining
* a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
*
* The above copyright notice and this permission notice shall be
* included in all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
* NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
* LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
* OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
* WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*
*/
#include "lf_ring_buffer.h"
#include "lf_portable_cas.h"
#include <stdlib.h>
#include <string.h>
#include <time.h>
//#define DEBUG_LFR_RING 1
#ifdef DEBUG_LFR_RING
#include <stdio.h>
#define _LOG_( ... ) fprintf(stdout,__VA_ARGS__)
#else
#define _LOG_( ... )
#endif
#define BACKOFF_NANO_SLEEP 100
/* initialize an empty lf_ring_buffer struct */
lf_ring_buffer_t* lf_ring_buffer_create( size_t n_buf ) {
/* alloc ring_buffer struct */
lf_ring_buffer_t *r = malloc(sizeof(lf_ring_buffer_t));
if(r==NULL) return NULL;
/* */
r->buffer = malloc(LFRB_BUFFER_SIZE*n_buf);
if(r->buffer==NULL) {
free(r);
return NULL;
}
memset(r->buffer,0,LFRB_BUFFER_SIZE*n_buf);
r->n_buf = n_buf;
r->read_from = -1;
r->write_to = 0;
return r;
}
/* destroy an lf_ring_buffer strcture */
void lf_ring_buffer_destroy( lf_ring_buffer_t *r ) {
free(r->buffer);
free(r);
}
/* write data into the ring buffer */
int lf_ring_buffer_write( lf_ring_buffer_t *r, void *data, int flags ) {
int idx, next;
struct timespec backoff;
/* reserve a buffer */
for(;;){
idx = r->write_to;
if(LFRB_IS_AVAILABLE( r->buffer[idx] ) ) {
/* read_from==idx means that the buffer is full and that a writer thread which at first reserved this buffer
* hasn't had enough CPU cycles to call MARK_AS_FILLED
*/
if( r->read_from!=idx ) {
next = idx+1;
if (next==r->n_buf) next=0;
/* what might have happend between IS_AVAILABLE and now :
* - a writter has reserved this buffer => write_to has moved => CAS fails
* - a reader has consumed a buffer => read_from has moved => we've got more space
*/
_LOG_( "write: CAS %d %d %d\n", r->write_to, idx, next );
if( CompareAndSwapInt( &r->write_to, idx, next ) ) {
/* !!!!!!!!!!!!!! WARNING !!!!!!!!!!!!!!!!!
* - if the ring is empty before this write operation (r->read_from==-1 or latest idx)
* - and n_buf other threads execute this same function before the next CAS is finished
* then, the last thread will :
* - see this buffer as available
* - and see the ring as empty instead of full !!!!!
* so it will ends with two threads writing on this buffer
*/
if(r->read_from==-1) CompareAndSwapInt( &r->read_from, -1, idx );
break;
}
} else {
_LOG_("write: ring full %d %d\n",r->read_from,idx);
if(IS_NOT_BLOCKING(flags)) return -1;
backoff.tv_sec = 0;
backoff.tv_nsec = BACKOFF_NANO_SLEEP;
nanosleep(&backoff,NULL);
}
} else {
_LOG_("write: buffer not available\n");
if(IS_NOT_BLOCKING(flags)) return -1;
backoff.tv_sec = 0;
backoff.tv_nsec = BACKOFF_NANO_SLEEP;
nanosleep(&backoff,NULL);
}
}
/* fill this buffer and mark it as filled */
memcpy( LFRB_DATA_PTR(r->buffer[idx]), data, LFRB_DATA_SIZE );
LFRB_MARK_AS_FILLED( r->buffer[idx] );
return 0;
}
/* read data from the ring buffer */
int lf_ring_buffer_read( lf_ring_buffer_t *r, void *data, int flags ) {
int idx, next;
struct timespec backoff;
for(;;) {
idx = r->read_from;
if( !(LFRB_IS_AVAILABLE( r->buffer[idx] )) && r->read_from!=-1 ) {
next = idx+1;
if (next==r->n_buf) next=0;
/* will do bad things if data dst buffer is too small !! */
memcpy( data, LFRB_DATA_PTR(r->buffer[idx]), LFRB_DATA_SIZE );
_LOG_( "read: CAS %d %d %d\n", r->read_from, idx, next );
if( CompareAndSwapInt( &r->read_from, idx, next ) ) {
if(r->read_from==r->write_to) {
/* the buffer is empty but writers will see it as full */
_LOG_( "read: empty CAS %d %d %d\n", r->read_from, next, -1 );
CompareAndSwapInt( &r->read_from, next, -1 );
}
break;
}
}
_LOG_("read: ring empty\n");
if(IS_NOT_BLOCKING(flags)) return -1;
backoff.tv_sec = 0;
backoff.tv_nsec = BACKOFF_NANO_SLEEP;
nanosleep(&backoff,NULL);
}
/* finish the read process */
LFRB_MARK_AS_READ( r->buffer[idx] );
return 0;
}
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