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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_ringbuffer.h"
#include "lf_portable_cas.h"
#include <stdlib.h>
#include <string.h>
#include <time.h>
//#define DEBUG_LFRB_KO 1
//#define DEBUG_LFRB_CAS 1
//#define DEBUG_LFRB 1
#ifdef DEBUG_LFRB
#include <stdio.h>
#define _LOG_KO_( ... ) fprintf(stdout,__VA_ARGS__)
#define _LOG_CAS_( ... )fprintf(stdout,__VA_ARGS__)
#elif defined DEBUG_LFRB_CAS
#include <stdio.h>
#define _LOG_KO_( ... )
#define _LOG_CAS_( ... )fprintf(stdout,__VA_ARGS__)
#elif defined DEBUG_LFRB_KO
#include <stdio.h>
#define _LOG_KO_( ... ) fprintf(stdout,__VA_ARGS__)
#define _LOG_CAS_( ... )
#else
#define _LOG_KO_( ... )
#define _LOG_CAS_( ... )
#endif
#define BACKOFF_NANO_SLEEP 10
#define USHORTMAX 0xffff
/* An unsigned int (indexes) is used to store both read_from and write_to indexes
* so that 32 bits compare and swap may be used to update both in one atomic instruction call.
* To be able to differenciate an empty buffer from a full buffer,
* read_from part of indexes is set to 0xffff (USHORTMAX) when the buffer is empty.
* Thus the maximum size of the buffer is 0xffff-1 = 65534 elements
*/
/* initialize an empty lf_ringbuffer struct */
lf_ringbuffer_t* lf_ringbuffer_create( size_t n_buf ) {
if(n_buf>=USHORTMAX) {
return NULL;
}
/* alloc ringbuffer struct */
lf_ringbuffer_t *r = malloc(sizeof(lf_ringbuffer_t));
if(r==NULL) return NULL;
/* alloc buffer */
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->indexes = (unsigned int)(USHORTMAX<<16) | (unsigned int)0;
return r;
}
/* destroy an lf_ringbuffer struct */
void lf_ringbuffer_destroy( lf_ringbuffer_t *r ) {
free(r->buffer);
free(r);
}
/* return 1 if is empty */
int lf_ringbuffer_empty( lf_ringbuffer_t *r ) { return (r->indexes>>16)==USHORTMAX; }
/* return count of filled buffers */
size_t lf_ringbuffer_read_size( lf_ringbuffer_t *r ) {
unsigned int write_to, read_from;
read_from = (r->indexes)>>16;
if(read_from==USHORTMAX) return 0;
write_to = (r->indexes)&0xffff;
if(write_to>read_from) {
return write_to-read_from;
} else {
return r->n_buf-read_from+write_to;
}
}
/* return count of available buffers */
size_t lf_ringbuffer_write_size( lf_ringbuffer_t *r ) {
unsigned int write_to, read_from;
read_from = (r->indexes)>>16;
if(read_from==USHORTMAX) return r->n_buf;
write_to = (r->indexes)&0xffff;
if(write_to>read_from) {
return r->n_buf-write_to+read_from;
} else {
return read_from-write_to;
}
}
/* write data into the ring buffer */
int lf_ringbuffer_write( lf_ringbuffer_t *r, void *data, int flags ) {
unsigned int current, next;
unsigned int write_to, read_from;
struct timespec backoff;
int backoff_time = BACKOFF_NANO_SLEEP;
/* reserve a buffer */
for(;;){
/* copy indexes and split it */
current = r->indexes;
write_to = current&0xffff;
read_from = current>>16;
/*
* check if the buffer is available,
* if read_from==write_to the buffer is full
* if it is available and full, it means that a writer thread which reserved this buffer
* hadn't had enough CPU cycles to call MARK_AS_FILLED
*/
if( LFRB_IS_AVAILABLE( r->buffer[write_to] ) && read_from!=write_to ) {
next = write_to+1;
if (next==r->n_buf) next=0;
/* set read_from to write_to if needed */
if (read_from==USHORTMAX) {
next |= write_to<<16;
} else {
next |= read_from<<16;
}
/* try to update indexes */
_LOG_CAS_( "write: CAS %u %u %u\n", r->indexes, current, next );
if( CompareAndSwapInt( &r->indexes, current, next ) ) break;
} else {
_LOG_KO_("write: impossible : wt:%d rf:%d wa:%d\n",write_to,read_from,LFRB_IS_AVAILABLE(r->buffer[write_to]));
if(IS_NOT_BLOCKING(flags)) return -1;
}
/* sleep */
backoff.tv_sec = 0;
backoff.tv_nsec = backoff_time;
nanosleep(&backoff,NULL);
backoff_time += BACKOFF_NANO_SLEEP;
}
/* fill this buffer and mark it as filled */
memcpy( LFRB_DATA_PTR(r->buffer[write_to]), data, LFRB_DATA_SIZE );
LFRB_MARK_AS_FILLED( r->buffer[write_to] );
return 0;
}
/* read data from the ring buffer */
int lf_ringbuffer_read( lf_ringbuffer_t *r, void *data, int flags ) {
unsigned int current, next;
unsigned int write_to, read_from, tmp;
struct timespec backoff;
int backoff_time = BACKOFF_NANO_SLEEP;
for(;;) {
/* copy indexes and split it */
current = r->indexes;
write_to = current&0xffff;
read_from = current>>16;
/*
* the buffer may be non empty but available if a writer thread hadn't had enough CPU cycles to mark the buffer as filled
*/
if( read_from==USHORTMAX || LFRB_IS_AVAILABLE( r->buffer[read_from] ) ) {
_LOG_KO_("read : impossible : wt:%d rf:%d ra:%d\n",write_to,read_from,LFRB_IS_AVAILABLE(r->buffer[read_from]));
if(IS_NOT_BLOCKING(flags)) return -1;
} else {
tmp = read_from +1;
if (tmp==r->n_buf) tmp=0;
/* set the buffer empty if needed */
if (tmp==write_to) {
tmp = USHORTMAX;
}
next = tmp<<16 | write_to;
/* try to update indexes */
_LOG_CAS_( "read: CAS %u %u %u\n", r->indexes, current, next );
if( CompareAndSwapInt( &r->indexes, current , next ) ) break;
}
/* sleep */
backoff.tv_sec = 0;
backoff.tv_nsec = backoff_time;
nanosleep(&backoff,NULL);
backoff_time += BACKOFF_NANO_SLEEP;
}
/* copy this buffer and mark it as read */
memcpy( data, LFRB_DATA_PTR(r->buffer[read_from]), LFRB_DATA_SIZE );
LFRB_MARK_AS_READ( r->buffer[read_from] );
return 0;
}
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