void *rqueue_read(rqueue_t *rb) {
int i;
void *v = NULL;
for (i = 0; i < RQUEUE_MAX_RETRIES; i++) {
if (__builtin_expect(ATOMIC_CAS(rb->read_sync, 0, 1), 1)) {
rqueue_page_t *head = ATOMIC_READ(rb->head);
rqueue_page_t *commit = ATOMIC_READ(rb->commit);
rqueue_page_t *tail = ATOMIC_READ(rb->tail);
rqueue_page_t *next = ATOMIC_READ(head->next);
rqueue_page_t *old_next = ATOMIC_READ(rb->reader->next);
if (rb->reader == commit || (head == tail && commit != tail) || ATOMIC_READ(rb->writes) == 0)
{ // nothing to read
ATOMIC_CAS(rb->read_sync, 1, 0);
break;
}
if (ATOMIC_CAS(rb->reader->next, old_next, RQUEUE_FLAG_ON(next, RQUEUE_FLAG_HEAD))) {
rb->reader->prev = head->prev;
if (ATOMIC_CAS(head->prev->next, RQUEUE_FLAG_ON(head, RQUEUE_FLAG_HEAD), rb->reader)) {
ATOMIC_CAS(rb->head, head, next);
next->prev = rb->reader;
rb->reader = head;
/*
rb->reader->next = next;
rb->reader->prev = next->prev;
*/
v = ATOMIC_READ(rb->reader->value);
ATOMIC_CAS(rb->reader->value, v, NULL);
ATOMIC_INCREMENT(rb->reads);
ATOMIC_CAS(rb->read_sync, 1, 0);
break;
} else {
fprintf(stderr, "head swap failed\n");
}
} else {
fprintf(stderr, "reader->next swap failed\n");
}
ATOMIC_CAS(rb->read_sync, 1, 0);
}
}
return v;
}
rqueue_t *rqueue_create(size_t size, rqueue_mode_t mode) {
size_t i;
rqueue_t *rb = calloc(1, sizeof(rqueue_t));
if (!rb)
return NULL;
rb->size = (size > RQUEUE_MIN_SIZE) ? size : RQUEUE_MIN_SIZE;
rb->mode = mode;
for (i = 0; i < size; i++) {
rqueue_page_t *page = calloc(1, sizeof(rqueue_page_t));
if (!page) {
free(rb);
// TODO - free the pages allocated so far
return NULL;
}
if (!rb->head) {
rb->head = rb->tail = page;
} else if (rb->tail) {
rb->tail->next = page;
}
page->prev = rb->tail;
rb->tail = page;
}
if (!rb->head || !rb->tail) {
free(rb);
return NULL;
}
// close the ringbuffer
rb->head->prev = rb->tail;
rb->tail->next = rb->head;
rb->tail->next = RQUEUE_FLAG_ON(rb->tail->next, RQUEUE_FLAG_HEAD);
rb->tail = rb->head;
rb->commit = rb->tail;
// the reader page is out of the ringbuffer
rb->reader = calloc(1, sizeof(rqueue_page_t));
if (!rb->reader) {
free(rb);
return NULL;
}
rb->reader->prev = rb->head->prev;
rb->reader->next = rb->head;
return rb;
}
int rqueue_write(rqueue_t *rb, void *value) {
int retries = 0;
int did_update = 0;
int did_move_head = 0;
rqueue_page_t *temp_page = NULL;
rqueue_page_t *next_page = NULL;
rqueue_page_t *tail = NULL;
rqueue_page_t *head = NULL;
rqueue_page_t *commit;
ATOMIC_INCREMENT(rb->num_writers);
do {
temp_page = ATOMIC_READ(rb->tail);
commit = ATOMIC_READ(rb->commit);
next_page = RQUEUE_FLAG_OFF(ATOMIC_READ(temp_page->next), RQUEUE_FLAG_ALL);
head = ATOMIC_READ(rb->head);
if (rb->mode == RQUEUE_MODE_BLOCKING) {
if (temp_page == commit && next_page == head) {
if (ATOMIC_READ(rb->writes) - ATOMIC_READ(rb->reads) != 0) {
//fprintf(stderr, "No buffer space\n");
if (ATOMIC_READ(rb->num_writers) == 1)
ATOMIC_CAS(rb->commit, ATOMIC_READ(rb->commit), ATOMIC_READ(rb->tail));
ATOMIC_DECREMENT(rb->num_writers);
return -2;
}
} else if (next_page == head) {
if (ATOMIC_READ(rb->num_writers) == 1) {
tail = temp_page;
break;
} else {
if (ATOMIC_READ(rb->num_writers) == 1)
ATOMIC_CAS(rb->commit, ATOMIC_READ(rb->commit), ATOMIC_READ(rb->tail));
ATOMIC_DECREMENT(rb->num_writers);
return -2;
}
}
}
tail = ATOMIC_CAS_RETURN(rb->tail, temp_page, next_page);
} while (tail != temp_page && !(RQUEUE_CHECK_FLAG(ATOMIC_READ(tail->next), RQUEUE_FLAG_UPDATE)) && retries++ < RQUEUE_MAX_RETRIES);
if (!tail) {
if (ATOMIC_READ(rb->num_writers) == 1)
ATOMIC_CAS(rb->commit, ATOMIC_READ(rb->commit), ATOMIC_READ(rb->tail));
ATOMIC_DECREMENT(rb->num_writers);
return -1;
}
rqueue_page_t *nextp = RQUEUE_FLAG_OFF(ATOMIC_READ(tail->next), RQUEUE_FLAG_ALL);
if (ATOMIC_CAS(tail->next, RQUEUE_FLAG_ON(nextp, RQUEUE_FLAG_HEAD), RQUEUE_FLAG_ON(nextp, RQUEUE_FLAG_UPDATE))) {
did_update = 1;
//fprintf(stderr, "Did update head pointer\n");
if (rb->mode == RQUEUE_MODE_OVERWRITE) {
// we need to advance the head if in overwrite mode ...otherwise we must stop
//fprintf(stderr, "Will advance head and overwrite old data\n");
rqueue_page_t *nextpp = RQUEUE_FLAG_OFF(ATOMIC_READ(nextp->next), RQUEUE_FLAG_ALL);
if (ATOMIC_CAS(nextp->next, nextpp, RQUEUE_FLAG_ON(nextpp, RQUEUE_FLAG_HEAD))) {
if (ATOMIC_READ(rb->tail) != next_page) {
ATOMIC_CAS(nextp->next, RQUEUE_FLAG_ON(nextpp, RQUEUE_FLAG_HEAD), nextpp);
} else {
ATOMIC_CAS(rb->head, head, nextpp);
did_move_head = 1;
}
}
}
}
void *old_value = ATOMIC_READ(tail->value);
ATOMIC_CAS(tail->value, old_value, value);
if (old_value && rb->free_value_cb)
rb->free_value_cb(old_value);
if (did_update) {
//fprintf(stderr, "Try restoring head pointer\n");
ATOMIC_CAS(tail->next,
RQUEUE_FLAG_ON(nextp, RQUEUE_FLAG_UPDATE),
did_move_head
? RQUEUE_FLAG_OFF(nextp, RQUEUE_FLAG_ALL)
: RQUEUE_FLAG_ON(nextp, RQUEUE_FLAG_HEAD));
//fprintf(stderr, "restored head pointer\n");
}
ATOMIC_INCREMENT(rb->writes);
if (ATOMIC_READ(rb->num_writers) == 1)
ATOMIC_CAS(rb->commit, ATOMIC_READ(rb->commit), tail);
ATOMIC_DECREMENT(rb->num_writers);
return 0;
}
