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/*
* File : lfq.c
* Author : Jérémy Zurcher <jeremy@asynk.ch>
* Date : 01/11/09
* 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_fifo.h"
#include "stdlib.h"
union ptr_u {
lf_pointer_t ptr;
volatile long long concat;
};
/* initialize an empty lf_fifo structure */
void lf_fifo_init( lf_fifo_t *q ) {
q->head.ptr = q->tail.ptr = NULL;
q->head.count = q->tail.count = 0;
}
/* push a node at the tail of q */
void lf_fifo_push( lf_fifo_t *q, lf_pointer_t *node ) {
lf_pointer_t tail;
lf_pointer_t last;
lf_pointer_t tmp;
/* init node */
node->ptr = NULL;
node->count = 0;
/* set tmp to point to node */
tmp.ptr = node;
tmp.count = 1;
for(;;) {
/* snapshot tail */
tail = q->tail;
/* nothing in tail link as first node */
if ( tail.ptr==NULL && cas( &q->tail, tail, tmp ) ) { /* TODO right place ?? */
q->head.ptr = node;
/* q->head.count = 1; ??? */
return;
} else {
/* snapshot last through tail */
last = *tail.ptr;
/* if tail is still consistant */
if (((union ptr_u)tail).concat == ((union ptr_u)q->tail).concat) {
/* if last is the last node */
if (last.ptr == NULL) {
tmp.count = last.count+1;
if ( cas( tail.ptr, last, tmp ) ) break;
} else {
/* try to swing tail to the next node */
last.count = tail.count+1;
cas( &q->tail, tail, last );
}
}
}
}
/* try to swing tail to the next node */
tmp.count = tail.count+1;
cas( &q->tail, tail, tmp );
}
/* pop a node from the head of q */
lf_pointer_t* pop( lf_fifo_t *q ) {
lf_pointer_t head;
lf_pointer_t tail;
lf_pointer_t tmp;
lf_pointer_t *node;
for(;;) {
/* snapshot head */
head = q->head;
/* return NULL if queue is empty */
if (head.ptr == NULL) { return NULL; } /* TODO before snapshot using q-> ?? */
/* snapshot tail */
tail = q->tail;
/* if there is only one node in the queue */
if ( tail.ptr == head.ptr ) {
/* tail points to NULL */
tmp.ptr = NULL;
tmp.count = tail.count+1;
cas( &q->tail, tail, tmp );
} else {
/* get the node ptr */
node = (lf_pointer_t *)head.ptr;
/* get the next head ready */
tmp.ptr = node->ptr;
tmp.count = head.count+1;
if ( cas( &q->head, head, tmp ) ) break;
}
}
return node;
}
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