On Thu, Dec 13, 2012 at 06:44:56AM -0500, Mathieu Desnoyers wrote:
> I noticed that in addition to having:
>
> - push/enqueue returning whether the stack/queue was empty prior to the
> operation,
> - pop_all/splice, by nature, emptying the stack/queue,
>
> it can be interesting to make pop/dequeue operations return whether they
> are returning the last element of the stack/queue (therefore emptying
> it). This allow extending the test-cases covering the number of empty
> stack/queue encountered by both push/enqueuer and pop/dequeuer threads
> not only to push/enqueue paired with pop_all/splice, but also to
> pop/dequeue.
>
> In the case of wfstack, this unfortunately requires to modify an already
> exposed API. As a RFC, one question we should answer is how we want to
> handle the way forward: should we add new functions to the wfstack API
> and leave the existing ones alone ?
>
> Thoughts ?
Hmmm... What is the use case, given that a push might happen immediately
after the pop said that the stack/queue was empty? Of course, if we
somehow know that there are no concurrent pushes, we could instead
check for empty.
So what am I missing here?
Thanx, Paul
> Thanks,
>
> Mathieu
>
> ---
> diff --git a/tests/test_urcu_wfcq.c b/tests/test_urcu_wfcq.c
> index 91285a5..de9566d 100644
> --- a/tests/test_urcu_wfcq.c
> +++ b/tests/test_urcu_wfcq.c
> @@ -168,6 +168,7 @@ static DEFINE_URCU_TLS(unsigned long long,
> nr_successful_dequeues);
> static DEFINE_URCU_TLS(unsigned long long, nr_successful_enqueues);
> static DEFINE_URCU_TLS(unsigned long long, nr_empty_dest_enqueues);
> static DEFINE_URCU_TLS(unsigned long long, nr_splice);
> +static DEFINE_URCU_TLS(unsigned long long, nr_dequeue_last);
>
> static unsigned int nr_enqueuers;
> static unsigned int nr_dequeuers;
> @@ -228,11 +229,15 @@ fail:
> static void do_test_dequeue(enum test_sync sync)
> {
> struct cds_wfcq_node *node;
> + bool last;
>
> if (sync == TEST_SYNC_MUTEX)
> - node = cds_wfcq_dequeue_blocking(&head, &tail);
> + node = cds_wfcq_dequeue_blocking(&head, &tail, &last);
> else
> - node = __cds_wfcq_dequeue_blocking(&head, &tail);
> + node = __cds_wfcq_dequeue_blocking(&head, &tail, &last);
> +
> + if (last)
> + URCU_TLS(nr_dequeue_last)++;
>
> if (node) {
> free(node);
> @@ -263,6 +268,7 @@ static void do_test_splice(enum test_sync sync)
> break;
> case CDS_WFCQ_RET_DEST_EMPTY:
> URCU_TLS(nr_splice)++;
> + URCU_TLS(nr_dequeue_last)++;
> /* ok */
> break;
> case CDS_WFCQ_RET_DEST_NON_EMPTY:
> @@ -325,16 +331,21 @@ static void *thr_dequeuer(void *_count)
> count[0] = URCU_TLS(nr_dequeues);
> count[1] = URCU_TLS(nr_successful_dequeues);
> count[2] = URCU_TLS(nr_splice);
> + count[3] = URCU_TLS(nr_dequeue_last);
> return ((void*)2);
> }
>
> -static void test_end(unsigned long long *nr_dequeues)
> +static void test_end(unsigned long long *nr_dequeues,
> + unsigned long long *nr_dequeue_last)
> {
> struct cds_wfcq_node *node;
> + bool last;
>
> do {
> - node = cds_wfcq_dequeue_blocking(&head, &tail);
> + node = cds_wfcq_dequeue_blocking(&head, &tail, &last);
> if (node) {
> + if (last)
> + (*nr_dequeue_last)++;
> free(node);
> (*nr_dequeues)++;
> }
> @@ -367,7 +378,7 @@ int main(int argc, char **argv)
> unsigned long long tot_successful_enqueues = 0,
> tot_successful_dequeues = 0,
> tot_empty_dest_enqueues = 0,
> - tot_splice = 0;
> + tot_splice = 0, tot_dequeue_last = 0;
> unsigned long long end_dequeues = 0;
> int i, a, retval = 0;
>
> @@ -480,7 +491,7 @@ int main(int argc, char **argv)
> tid_enqueuer = malloc(sizeof(*tid_enqueuer) * nr_enqueuers);
> tid_dequeuer = malloc(sizeof(*tid_dequeuer) * nr_dequeuers);
> count_enqueuer = malloc(3 * sizeof(*count_enqueuer) * nr_enqueuers);
> - count_dequeuer = malloc(3 * sizeof(*count_dequeuer) * nr_dequeuers);
> + count_dequeuer = malloc(4 * sizeof(*count_dequeuer) * nr_dequeuers);
> cds_wfcq_init(&head, &tail);
>
> next_aff = 0;
> @@ -493,7 +504,7 @@ int main(int argc, char **argv)
> }
> for (i = 0; i < nr_dequeuers; i++) {
> err = pthread_create(&tid_dequeuer[i], NULL, thr_dequeuer,
> - &count_dequeuer[3 * i]);
> + &count_dequeuer[4 * i]);
> if (err != 0)
> exit(1);
> }
> @@ -533,34 +544,37 @@ int main(int argc, char **argv)
> err = pthread_join(tid_dequeuer[i], &tret);
> if (err != 0)
> exit(1);
> - tot_dequeues += count_dequeuer[3 * i];
> - tot_successful_dequeues += count_dequeuer[3 * i + 1];
> - tot_splice += count_dequeuer[3 * i + 2];
> + tot_dequeues += count_dequeuer[4 * i];
> + tot_successful_dequeues += count_dequeuer[4 * i + 1];
> + tot_splice += count_dequeuer[4 * i + 2];
> + tot_dequeue_last += count_dequeuer[4 * i + 3];
> }
>
> - test_end(&end_dequeues);
> + test_end(&end_dequeues, &tot_dequeue_last);
>
> printf_verbose("total number of enqueues : %llu, dequeues %llu\n",
> tot_enqueues, tot_dequeues);
> printf_verbose("total number of successful enqueues : %llu, "
> "enqueues to empty dest : %llu, "
> "successful dequeues %llu, "
> - "splice : %llu\n",
> + "splice : %llu, dequeue_last : %llu\n",
> tot_successful_enqueues,
> tot_empty_dest_enqueues,
> tot_successful_dequeues,
> - tot_splice);
> + tot_splice, tot_dequeue_last);
> printf("SUMMARY %-25s testdur %4lu nr_enqueuers %3u wdelay %6lu "
> "nr_dequeuers %3u "
> "rdur %6lu nr_enqueues %12llu nr_dequeues %12llu "
> "successful enqueues %12llu enqueues to empty dest %12llu "
> "successful dequeues %12llu splice %12llu "
> + "dequeue_last %llu "
> "end_dequeues %llu nr_ops %12llu\n",
> argv[0], duration, nr_enqueuers, wdelay,
> nr_dequeuers, rduration, tot_enqueues, tot_dequeues,
> tot_successful_enqueues,
> tot_empty_dest_enqueues,
> - tot_successful_dequeues, tot_splice, end_dequeues,
> + tot_successful_dequeues, tot_splice, tot_dequeue_last,
> + end_dequeues,
> tot_enqueues + tot_dequeues);
>
> if (tot_successful_enqueues != tot_successful_dequeues + end_dequeues) {
> @@ -576,12 +590,11 @@ int main(int argc, char **argv)
> * exactly as many empty queues than the number of non-empty
> * src splice.
> */
> - if (test_wait_empty && test_splice && !test_dequeue
> - && tot_empty_dest_enqueues != tot_splice) {
> + if (tot_empty_dest_enqueues != tot_dequeue_last) {
> printf("WARNING! Discrepancy between empty enqueue (%llu) and "
> - "number of non-empty splice (%llu)\n",
> + "number of dequeue of last element (%llu)\n",
> tot_empty_dest_enqueues,
> - tot_splice);
> + tot_dequeue_last);
> retval = 1;
> }
> free(count_enqueuer);
> diff --git a/tests/test_urcu_wfs.c b/tests/test_urcu_wfs.c
> index 259ca24..6c54153 100644
> --- a/tests/test_urcu_wfs.c
> +++ b/tests/test_urcu_wfs.c
> @@ -171,6 +171,7 @@ static DEFINE_URCU_TLS(unsigned long long,
> nr_successful_dequeues);
> static DEFINE_URCU_TLS(unsigned long long, nr_successful_enqueues);
> static DEFINE_URCU_TLS(unsigned long long, nr_empty_dest_enqueues);
> static DEFINE_URCU_TLS(unsigned long long, nr_pop_all);
> +static DEFINE_URCU_TLS(unsigned long long, nr_pop_last);
>
> static unsigned int nr_enqueuers;
> static unsigned int nr_dequeuers;
> @@ -230,14 +231,17 @@ fail:
> static void do_test_pop(enum test_sync sync)
> {
> struct cds_wfs_node *node;
> + bool last;
>
> if (sync == TEST_SYNC_MUTEX)
> cds_wfs_pop_lock(&s);
> - node = __cds_wfs_pop_blocking(&s);
> + node = __cds_wfs_pop_blocking(&s, &last);
> if (sync == TEST_SYNC_MUTEX)
> cds_wfs_pop_unlock(&s);
>
> if (node) {
> + if (last)
> + URCU_TLS(nr_pop_last)++;
> free(node);
> URCU_TLS(nr_successful_dequeues)++;
> }
> @@ -260,6 +264,7 @@ static void do_test_pop_all(enum test_sync sync)
> return;
>
> URCU_TLS(nr_pop_all)++;
> + URCU_TLS(nr_pop_last)++;
>
> cds_wfs_for_each_blocking_safe(head, node, n) {
> free(node);
> @@ -308,24 +313,30 @@ static void *thr_dequeuer(void *_count)
>
> printf_verbose("dequeuer thread_end, thread id : %lx, tid %lu, "
> "dequeues %llu, successful_dequeues %llu "
> - "pop_all %llu\n",
> + "pop_all %llu pop_last %llu\n",
> pthread_self(),
> (unsigned long) gettid(),
> URCU_TLS(nr_dequeues), URCU_TLS(nr_successful_dequeues),
> - URCU_TLS(nr_pop_all));
> + URCU_TLS(nr_pop_all),
> + URCU_TLS(nr_pop_last));
> count[0] = URCU_TLS(nr_dequeues);
> count[1] = URCU_TLS(nr_successful_dequeues);
> count[2] = URCU_TLS(nr_pop_all);
> + count[3] = URCU_TLS(nr_pop_last);
> return ((void*)2);
> }
>
> -static void test_end(struct cds_wfs_stack *s, unsigned long long
> *nr_dequeues)
> +static void test_end(struct cds_wfs_stack *s, unsigned long long
> *nr_dequeues,
> + unsigned long long *nr_pop_last)
> {
> struct cds_wfs_node *node;
> + bool last;
>
> do {
> - node = cds_wfs_pop_blocking(s);
> + node = cds_wfs_pop_blocking(s, &last);
> if (node) {
> + if (last)
> + (*nr_pop_last)++;
> free(node);
> (*nr_dequeues)++;
> }
> @@ -358,7 +369,7 @@ int main(int argc, char **argv)
> unsigned long long tot_successful_enqueues = 0,
> tot_successful_dequeues = 0,
> tot_empty_dest_enqueues = 0,
> - tot_pop_all = 0;
> + tot_pop_all = 0, tot_pop_last = 0;
> unsigned long long end_dequeues = 0;
> int i, a, retval = 0;
>
> @@ -471,7 +482,7 @@ int main(int argc, char **argv)
> tid_enqueuer = malloc(sizeof(*tid_enqueuer) * nr_enqueuers);
> tid_dequeuer = malloc(sizeof(*tid_dequeuer) * nr_dequeuers);
> count_enqueuer = malloc(3 * sizeof(*count_enqueuer) * nr_enqueuers);
> - count_dequeuer = malloc(3 * sizeof(*count_dequeuer) * nr_dequeuers);
> + count_dequeuer = malloc(4 * sizeof(*count_dequeuer) * nr_dequeuers);
> cds_wfs_init(&s);
>
> next_aff = 0;
> @@ -484,7 +495,7 @@ int main(int argc, char **argv)
> }
> for (i = 0; i < nr_dequeuers; i++) {
> err = pthread_create(&tid_dequeuer[i], NULL, thr_dequeuer,
> - &count_dequeuer[3 * i]);
> + &count_dequeuer[4 * i]);
> if (err != 0)
> exit(1);
> }
> @@ -524,34 +535,36 @@ int main(int argc, char **argv)
> err = pthread_join(tid_dequeuer[i], &tret);
> if (err != 0)
> exit(1);
> - tot_dequeues += count_dequeuer[3 * i];
> - tot_successful_dequeues += count_dequeuer[3 * i + 1];
> - tot_pop_all += count_dequeuer[3 * i + 2];
> + tot_dequeues += count_dequeuer[4 * i];
> + tot_successful_dequeues += count_dequeuer[4 * i + 1];
> + tot_pop_all += count_dequeuer[4 * i + 2];
> + tot_pop_last += count_dequeuer[4 * i + 3];
> }
>
> - test_end(&s, &end_dequeues);
> + test_end(&s, &end_dequeues, &tot_pop_last);
>
> printf_verbose("total number of enqueues : %llu, dequeues %llu\n",
> tot_enqueues, tot_dequeues);
> printf_verbose("total number of successful enqueues : %llu, "
> "enqueues to empty dest : %llu, "
> "successful dequeues %llu, "
> - "pop_all : %llu\n",
> + "pop_all : %llu, pop_last : %llu\n",
> tot_successful_enqueues,
> tot_empty_dest_enqueues,
> tot_successful_dequeues,
> - tot_pop_all);
> + tot_pop_all, tot_pop_last);
> printf("SUMMARY %-25s testdur %4lu nr_enqueuers %3u wdelay %6lu "
> "nr_dequeuers %3u "
> "rdur %6lu nr_enqueues %12llu nr_dequeues %12llu "
> "successful enqueues %12llu enqueues to empty dest %12llu "
> "successful dequeues %12llu pop_all %12llu "
> - "end_dequeues %llu nr_ops %12llu\n",
> + "pop_last %llu end_dequeues %llu nr_ops %12llu\n",
> argv[0], duration, nr_enqueuers, wdelay,
> nr_dequeuers, rduration, tot_enqueues, tot_dequeues,
> tot_successful_enqueues,
> tot_empty_dest_enqueues,
> - tot_successful_dequeues, tot_pop_all, end_dequeues,
> + tot_successful_dequeues, tot_pop_all, tot_pop_last,
> + end_dequeues,
> tot_enqueues + tot_dequeues);
> if (tot_successful_enqueues != tot_successful_dequeues + end_dequeues) {
> printf("WARNING! Discrepancy between nr succ. enqueues %llu vs "
> @@ -561,16 +574,14 @@ int main(int argc, char **argv)
> retval = 1;
> }
> /*
> - * If only using pop_all to dequeue, the enqueuer should see
> - * exactly as many empty queues than the number of non-empty
> - * stacks dequeued.
> + * The enqueuer should see exactly as many empty queues than the
> + * number of non-empty stacks dequeued.
> */
> - if (test_wait_empty && test_pop_all && !test_pop
> - && tot_empty_dest_enqueues != tot_pop_all) {
> + if (tot_empty_dest_enqueues != tot_pop_last) {
> printf("WARNING! Discrepancy between empty enqueue (%llu) and "
> - "number of non-empty pop_all (%llu)\n",
> + "number of pop last (%llu)\n",
> tot_empty_dest_enqueues,
> - tot_pop_all);
> + tot_pop_last);
> retval = 1;
> }
> free(count_enqueuer);
> diff --git a/urcu/static/wfcqueue.h b/urcu/static/wfcqueue.h
> index 4b3535a..33c99ed 100644
> --- a/urcu/static/wfcqueue.h
> +++ b/urcu/static/wfcqueue.h
> @@ -352,16 +352,23 @@ ___cds_wfcq_next_nonblocking(struct cds_wfcq_head *head,
> static inline struct cds_wfcq_node *
> ___cds_wfcq_dequeue(struct cds_wfcq_head *head,
> struct cds_wfcq_tail *tail,
> + bool *last,
> int blocking)
> {
> struct cds_wfcq_node *node, *next;
>
> - if (_cds_wfcq_empty(head, tail))
> + if (_cds_wfcq_empty(head, tail)) {
> + if (last)
> + *last = 0;
> return NULL;
> + }
>
> node = ___cds_wfcq_node_sync_next(&head->node, blocking);
> - if (!blocking && node == CDS_WFCQ_WOULDBLOCK)
> + if (!blocking && node == CDS_WFCQ_WOULDBLOCK) {
> + if (last)
> + *last = 0;
> return CDS_WFCQ_WOULDBLOCK;
> + }
>
> if ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
> /*
> @@ -379,8 +386,11 @@ ___cds_wfcq_dequeue(struct cds_wfcq_head *head,
> * content.
> */
> _cds_wfcq_node_init(&head->node);
> - if (uatomic_cmpxchg(&tail->p, node, &head->node) == node)
> + if (uatomic_cmpxchg(&tail->p, node, &head->node) == node) {
> + if (last)
> + *last = 1;
> return node;
> + }
> next = ___cds_wfcq_node_sync_next(node, blocking);
> /*
> * In nonblocking mode, if we would need to block to
> @@ -389,6 +399,8 @@ ___cds_wfcq_dequeue(struct cds_wfcq_head *head,
> */
> if (!blocking && next == CDS_WFCQ_WOULDBLOCK) {
> head->node.next = node;
> + if (last)
> + *last = 0;
> return CDS_WFCQ_WOULDBLOCK;
> }
> }
> @@ -400,6 +412,8 @@ ___cds_wfcq_dequeue(struct cds_wfcq_head *head,
>
> /* Load q->head.next before loading node's content */
> cmm_smp_read_barrier_depends();
> + if (last)
> + *last = 0;
> return node;
> }
>
> @@ -414,9 +428,9 @@ ___cds_wfcq_dequeue(struct cds_wfcq_head *head,
> */
> static inline struct cds_wfcq_node *
> ___cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head,
> - struct cds_wfcq_tail *tail)
> + struct cds_wfcq_tail *tail, bool *last)
> {
> - return ___cds_wfcq_dequeue(head, tail, 1);
> + return ___cds_wfcq_dequeue(head, tail, last, 1);
> }
>
> /*
> @@ -427,9 +441,9 @@ ___cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head,
> */
> static inline struct cds_wfcq_node *
> ___cds_wfcq_dequeue_nonblocking(struct cds_wfcq_head *head,
> - struct cds_wfcq_tail *tail)
> + struct cds_wfcq_tail *tail, bool *last)
> {
> - return ___cds_wfcq_dequeue(head, tail, 0);
> + return ___cds_wfcq_dequeue(head, tail, last, 0);
> }
>
> /*
> @@ -542,12 +556,12 @@ ___cds_wfcq_splice_nonblocking(
> */
> static inline struct cds_wfcq_node *
> _cds_wfcq_dequeue_blocking(struct cds_wfcq_head *head,
> - struct cds_wfcq_tail *tail)
> + struct cds_wfcq_tail *tail, bool *last)
> {
> struct cds_wfcq_node *retval;
>
> _cds_wfcq_dequeue_lock(head, tail);
> - retval = ___cds_wfcq_dequeue_blocking(head, tail);
> + retval = ___cds_wfcq_dequeue_blocking(head, tail, last);
> _cds_wfcq_dequeue_unlock(head, tail);
> return retval;
> }
> diff --git a/urcu/static/wfstack.h b/urcu/static/wfstack.h
> index 9bc9519..2ebda27 100644
> --- a/urcu/static/wfstack.h
> +++ b/urcu/static/wfstack.h
> @@ -161,23 +161,35 @@ ___cds_wfs_node_sync_next(struct cds_wfs_node *node,
> int blocking)
>
> static inline
> struct cds_wfs_node *
> -___cds_wfs_pop(struct cds_wfs_stack *s, int blocking)
> +___cds_wfs_pop(struct cds_wfs_stack *s, bool *last, int blocking)
> {
> struct cds_wfs_head *head, *new_head;
> struct cds_wfs_node *next;
>
> for (;;) {
> head = CMM_LOAD_SHARED(s->head);
> - if (___cds_wfs_end(head))
> + if (___cds_wfs_end(head)) {
> + if (last)
> + *last = 0;
> return NULL;
> + }
> next = ___cds_wfs_node_sync_next(&head->node, blocking);
> - if (!blocking && next == CDS_WFS_WOULDBLOCK)
> + if (!blocking && next == CDS_WFS_WOULDBLOCK) {
> + if (last)
> + *last = 0;
> return CDS_WFS_WOULDBLOCK;
> + }
> new_head = caa_container_of(next, struct cds_wfs_head, node);
> - if (uatomic_cmpxchg(&s->head, head, new_head) == head)
> + if (uatomic_cmpxchg(&s->head, head, new_head) == head) {
> + if (last)
> + *last = ___cds_wfs_end(new_head);
> return &head->node;
> - if (!blocking)
> + }
> + if (!blocking) {
> + if (last)
> + *last = 0;
> return CDS_WFS_WOULDBLOCK;
> + }
> /* busy-loop if head changed under us */
> }
> }
> @@ -200,9 +212,9 @@ ___cds_wfs_pop(struct cds_wfs_stack *s, int blocking)
> */
> static inline
> struct cds_wfs_node *
> -___cds_wfs_pop_blocking(struct cds_wfs_stack *s)
> +___cds_wfs_pop_blocking(struct cds_wfs_stack *s, bool *last)
> {
> - return ___cds_wfs_pop(s, 1);
> + return ___cds_wfs_pop(s, last, 1);
> }
>
> /*
> @@ -213,9 +225,9 @@ ___cds_wfs_pop_blocking(struct cds_wfs_stack *s)
> */
> static inline
> struct cds_wfs_node *
> -___cds_wfs_pop_nonblocking(struct cds_wfs_stack *s)
> +___cds_wfs_pop_nonblocking(struct cds_wfs_stack *s, bool *last)
> {
> - return ___cds_wfs_pop(s, 0);
> + return ___cds_wfs_pop(s, last, 0);
> }
>
> /*
> @@ -284,12 +296,12 @@ static inline void _cds_wfs_pop_unlock(struct
> cds_wfs_stack *s)
> */
> static inline
> struct cds_wfs_node *
> -_cds_wfs_pop_blocking(struct cds_wfs_stack *s)
> +_cds_wfs_pop_blocking(struct cds_wfs_stack *s, bool *last)
> {
> struct cds_wfs_node *retnode;
>
> _cds_wfs_pop_lock(s);
> - retnode = ___cds_wfs_pop_blocking(s);
> + retnode = ___cds_wfs_pop_blocking(s, last);
> _cds_wfs_pop_unlock(s);
> return retnode;
> }
> diff --git a/urcu/wfcqueue.h b/urcu/wfcqueue.h
> index b6be9f3..4b9e73b 100644
> --- a/urcu/wfcqueue.h
> +++ b/urcu/wfcqueue.h
> @@ -197,7 +197,8 @@ extern bool cds_wfcq_enqueue(struct cds_wfcq_head *head,
> */
> extern struct cds_wfcq_node *cds_wfcq_dequeue_blocking(
> struct cds_wfcq_head *head,
> - struct cds_wfcq_tail *tail);
> + struct cds_wfcq_tail *tail,
> + bool *last);
>
> /*
> * cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q.
> @@ -229,7 +230,8 @@ extern enum cds_wfcq_ret cds_wfcq_splice_blocking(
> */
> extern struct cds_wfcq_node *__cds_wfcq_dequeue_blocking(
> struct cds_wfcq_head *head,
> - struct cds_wfcq_tail *tail);
> + struct cds_wfcq_tail *tail,
> + bool *last);
>
> /*
> * __cds_wfcq_dequeue_nonblocking: dequeue a node from a wait-free queue.
> @@ -239,7 +241,8 @@ extern struct cds_wfcq_node *__cds_wfcq_dequeue_blocking(
> */
> extern struct cds_wfcq_node *__cds_wfcq_dequeue_nonblocking(
> struct cds_wfcq_head *head,
> - struct cds_wfcq_tail *tail);
> + struct cds_wfcq_tail *tail,
> + bool *last);
>
> /*
> * __cds_wfcq_splice_blocking: enqueue all src_q nodes at the end of dest_q.
> diff --git a/urcu/wfstack.h b/urcu/wfstack.h
> index 03fee8f..1e4b848 100644
> --- a/urcu/wfstack.h
> +++ b/urcu/wfstack.h
> @@ -147,7 +147,8 @@ extern int cds_wfs_push(struct cds_wfs_stack *s, struct
> cds_wfs_node *node);
> *
> * Calls __cds_wfs_pop_blocking with an internal pop mutex held.
> */
> -extern struct cds_wfs_node *cds_wfs_pop_blocking(struct cds_wfs_stack *s);
> +extern struct cds_wfs_node *cds_wfs_pop_blocking(struct cds_wfs_stack *s,
> + bool *last);
>
> /*
> * cds_wfs_pop_all_blocking: pop all nodes from a stack.
> @@ -219,7 +220,8 @@ extern void cds_wfs_pop_unlock(struct cds_wfs_stack *s);
> * 3) Ensuring that only ONE thread can call __cds_wfs_pop_blocking()
> * and __cds_wfs_pop_all(). (multi-provider/single-consumer scheme).
> */
> -extern struct cds_wfs_node *__cds_wfs_pop_blocking(struct cds_wfs_stack *s);
> +extern struct cds_wfs_node *__cds_wfs_pop_blocking(struct cds_wfs_stack *s,
> + bool *last);
>
> /*
> * __cds_wfs_pop_nonblocking: pop a node from the stack.
> @@ -227,7 +229,8 @@ extern struct cds_wfs_node *__cds_wfs_pop_blocking(struct
> cds_wfs_stack *s);
> * Same as __cds_wfs_pop_blocking, but returns CDS_WFS_WOULDBLOCK if
> * it needs to block.
> */
> -extern struct cds_wfs_node *__cds_wfs_pop_nonblocking(struct cds_wfs_stack
> *s);
> +extern struct cds_wfs_node *__cds_wfs_pop_nonblocking(struct cds_wfs_stack
> *s,
> + bool *last);
>
> /*
> * __cds_wfs_pop_all: pop all nodes from a stack.
> diff --git a/wfcqueue.c b/wfcqueue.c
> index ab0eb93..7baefdf 100644
> --- a/wfcqueue.c
> +++ b/wfcqueue.c
> @@ -68,9 +68,10 @@ void cds_wfcq_dequeue_unlock(struct cds_wfcq_head *head,
>
> struct cds_wfcq_node *cds_wfcq_dequeue_blocking(
> struct cds_wfcq_head *head,
> - struct cds_wfcq_tail *tail)
> + struct cds_wfcq_tail *tail,
> + bool *last)
> {
> - return _cds_wfcq_dequeue_blocking(head, tail);
> + return _cds_wfcq_dequeue_blocking(head, tail, last);
> }
>
> enum cds_wfcq_ret cds_wfcq_splice_blocking(
> @@ -85,16 +86,18 @@ enum cds_wfcq_ret cds_wfcq_splice_blocking(
>
> struct cds_wfcq_node *__cds_wfcq_dequeue_blocking(
> struct cds_wfcq_head *head,
> - struct cds_wfcq_tail *tail)
> + struct cds_wfcq_tail *tail,
> + bool *last)
> {
> - return ___cds_wfcq_dequeue_blocking(head, tail);
> + return ___cds_wfcq_dequeue_blocking(head, tail, last);
> }
>
> struct cds_wfcq_node *__cds_wfcq_dequeue_nonblocking(
> struct cds_wfcq_head *head,
> - struct cds_wfcq_tail *tail)
> + struct cds_wfcq_tail *tail,
> + bool *last)
> {
> - return ___cds_wfcq_dequeue_nonblocking(head, tail);
> + return ___cds_wfcq_dequeue_nonblocking(head, tail, last);
> }
>
> enum cds_wfcq_ret __cds_wfcq_splice_blocking(
> diff --git a/wfstack.c b/wfstack.c
> index 4ccb6b9..041703b 100644
> --- a/wfstack.c
> +++ b/wfstack.c
> @@ -48,9 +48,10 @@ int cds_wfs_push(struct cds_wfs_stack *s, struct
> cds_wfs_node *node)
> return _cds_wfs_push(s, node);
> }
>
> -struct cds_wfs_node *cds_wfs_pop_blocking(struct cds_wfs_stack *s)
> +struct cds_wfs_node *cds_wfs_pop_blocking(struct cds_wfs_stack *s,
> + bool *last)
> {
> - return _cds_wfs_pop_blocking(s);
> + return _cds_wfs_pop_blocking(s, last);
> }
>
> struct cds_wfs_head *cds_wfs_pop_all_blocking(struct cds_wfs_stack *s)
> @@ -83,14 +84,16 @@ void cds_wfs_pop_unlock(struct cds_wfs_stack *s)
> _cds_wfs_pop_unlock(s);
> }
>
> -struct cds_wfs_node *__cds_wfs_pop_blocking(struct cds_wfs_stack *s)
> +struct cds_wfs_node *__cds_wfs_pop_blocking(struct cds_wfs_stack *s,
> + bool *last)
> {
> - return ___cds_wfs_pop_blocking(s);
> + return ___cds_wfs_pop_blocking(s, last);
> }
>
> -struct cds_wfs_node *__cds_wfs_pop_nonblocking(struct cds_wfs_stack *s)
> +struct cds_wfs_node *__cds_wfs_pop_nonblocking(struct cds_wfs_stack *s,
> + bool *last)
> {
> - return ___cds_wfs_pop_nonblocking(s);
> + return ___cds_wfs_pop_nonblocking(s, last);
> }
>
> struct cds_wfs_head *__cds_wfs_pop_all(struct cds_wfs_stack *s)
>
> --
> Mathieu Desnoyers
> Operating System Efficiency R&D Consultant
> EfficiOS Inc.
> http://www.efficios.com
>
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