/*
 * 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 strcture */
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; }

/* 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;
}