[lttng-dev] [RFC PATCH] wfqueue: expand API, simplify implementation, small performance boost
Lai Jiangshan
eag0628 at gmail.com
Mon Aug 13 11:13:20 EDT 2012
On Sun, Aug 12, 2012 at 10:50 PM, Mathieu Desnoyers
<mathieu.desnoyers at efficios.com> wrote:
> This work is derived from the patch from Lai Jiangshan submitted as
> "urcu: new wfqueue implementation"
> (http://lists.lttng.org/pipermail/lttng-dev/2012-August/018379.html)
>
> Its changelog:
>
>> Some guys would be surprised by this fact:
>> There are already TWO implementations of wfqueue in urcu.
>>
>> The first one is in urcu/static/wfqueue.h:
>> 1) enqueue: exchange the tail and then update previous->next
>> 2) dequeue: wait for first node's next pointer and them shift, a dummy node
>> is introduced to avoid the queue->tail become NULL when shift.
>>
>> The second one shares some code with the first one, and the left code
>> are spreading in urcu-call-rcu-impl.h:
>> 1) enqueue: share with the first one
>> 2) no dequeue operation: and no shift, so it don't need dummy node,
>> Although the dummy node is queued when initialization, but it is removed
>> after the first dequeue_all operation in call_rcu_thread().
>> call_rcu_data_free() forgets to handle the dummy node if it is not removed.
>> 3)dequeue_all: record the old head and tail, and queue->head become the special
>> tail node.(atomic record the tail and change the tail).
>>
>> The second implementation's code are spreading, bad for review, and it is not
>> tested by tests/test_urcu_wfq.
>>
>> So we need a better implementation avoid the dummy node dancing and can service
>> both generic wfqueue APIs and dequeue_all API for call rcu.
>>
>> The new implementation:
>> 1) enqueue: share with the first one/original implementation.
>> 2) dequeue: shift when node count >= 2, cmpxchg when node count = 1.
>> no dummy node, save memory.
>> 3) dequeue_all: simply set queue->head.next to NULL, xchg the tail
>> and return the old head.next.
>>
>> More implementation details are in the code.
>> tests/test_urcu_wfq will be update in future for testing new APIs.
>
> The patch proposed by Lai brings a very interesting simplification to
> the single-node handling (which is kept here), and moves all queue
> handling code away from call_rcu implementation, back into the wfqueue
> code. This has the benefit to allow testing enhancements.
>
> I modified it so the API does not expose implementation details to the
> user (e.g. ___cds_wfq_node_sync_next). I added a "splice" operation and
> a for loop iterator which should allow wfqueue users to use the list
> very efficiently both from LGPL/GPL code and from non-LGPL-compatible
> code.
>
> Benchmarks performed on Intel(R) Core(TM) i7-3520M CPU @ 2.90GHz
> (dual-core, with hyperthreading)
>
> Benchmark invoked:
> test_urcu_wfq 2 2 10
>
> Only did 2 runs, but a small improvement seems to be clear for the
> dequeue speed:
>
> Before patch:
>
> testdur 10 nr_enqueuers 2 wdelay 0 nr_dequeuers 2 rdur 0 nr_enqueues 136251248 nr_dequeues 54694027 successful enqueues 136251248 successful dequeues 54693904 end_dequeues 81557344 nr_ops 190945275
> testdur 10 nr_enqueuers 2 wdelay 0 nr_dequeuers 2 rdur 0 nr_enqueues 137258881 nr_dequeues 54463340 successful enqueues 137258881 successful dequeues 54463238 end_dequeues 82795643 nr_ops 191722221
>
> After patch:
>
> testdur 10 nr_enqueuers 2 wdelay 0 nr_dequeuers 2 rdur 0 nr_enqueues 138589301 nr_dequeues 56911253 successful enqueues 138589301 successful dequeues 56910916 end_dequeues 81678385 nr_ops 195500554
> testdur 10 nr_enqueuers 2 wdelay 0 nr_dequeuers 2 rdur 0 nr_enqueues 139007622 nr_dequeues 57281502 successful enqueues 139007622 successful dequeues 57281348 end_dequeues 81726274 nr_ops 196289124
>
> Summary: Number of enqueues is slightly lower,
?!
I see the nr_enqueues and successful enqueues are both increased after
after patch.
> probably due to higher
> dequeue rate. Number of dequeue increased. Respective rate change is
> within 1% (slowdown) for enqueue, 2% (performance improvement) for
> dequeue. Overall number of operations (dequeue+enqueue) increased with
> the patch.
>
> We can verify that:
> successful enqueues - successful dequeues = end_dequeues
>
> For all runs (ensures correctness: no lost node).
>
> CC: Lai Jiangshan <laijs at cn.fujitsu.com>
> CC: Paul McKenney <paulmck at linux.vnet.ibm.com>
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> ---
> diff --git a/urcu-call-rcu-impl.h b/urcu-call-rcu-impl.h
> index 13b24ff..5363fe0 100644
> --- a/urcu-call-rcu-impl.h
> +++ b/urcu-call-rcu-impl.h
> @@ -21,6 +21,7 @@
> */
>
> #define _GNU_SOURCE
> +#define _LGPL_SOURCE
> #include <stdio.h>
> #include <pthread.h>
> #include <signal.h>
> @@ -220,10 +221,7 @@ static void call_rcu_wake_up(struct call_rcu_data *crdp)
> static void *call_rcu_thread(void *arg)
> {
> unsigned long cbcount;
> - struct cds_wfq_node *cbs;
> - struct cds_wfq_node **cbs_tail;
> - struct call_rcu_data *crdp = (struct call_rcu_data *)arg;
> - struct rcu_head *rhp;
> + struct call_rcu_data *crdp = (struct call_rcu_data *) arg;
> int rt = !!(uatomic_read(&crdp->flags) & URCU_CALL_RCU_RT);
> int ret;
>
> @@ -243,35 +241,29 @@ static void *call_rcu_thread(void *arg)
> cmm_smp_mb();
> }
> for (;;) {
> - if (&crdp->cbs.head != _CMM_LOAD_SHARED(crdp->cbs.tail)) {
> - while ((cbs = _CMM_LOAD_SHARED(crdp->cbs.head)) == NULL)
> - poll(NULL, 0, 1);
> - _CMM_STORE_SHARED(crdp->cbs.head, NULL);
> - cbs_tail = (struct cds_wfq_node **)
> - uatomic_xchg(&crdp->cbs.tail, &crdp->cbs.head);
> + struct cds_wfq_queue cbs_tmp;
> + struct cds_wfq_node *cbs;
> +
> + cds_wfq_init(&cbs_tmp);
> + __cds_wfq_splice_blocking(&cbs_tmp, &crdp->cbs);
> + if (!cds_wfq_empty(&cbs_tmp)) {
> synchronize_rcu();
> cbcount = 0;
> - do {
> - while (cbs->next == NULL &&
> - &cbs->next != cbs_tail)
> - poll(NULL, 0, 1);
> - if (cbs == &crdp->cbs.dummy) {
> - cbs = cbs->next;
> - continue;
> - }
> - rhp = (struct rcu_head *)cbs;
> - cbs = cbs->next;
> + __cds_wfq_for_each_blocking(&cbs_tmp, cbs) {
> + struct rcu_head *rhp;
> +
> + rhp = caa_container_of(cbs,
> + struct rcu_head, next);
> rhp->func(rhp);
cbs is freed hear, but it will be used in __cds_wfq_next_blocking().
Introduce __cds_wfq_for_each_blocking_safe() ?
> cbcount++;
> - } while (cbs != NULL);
> + }
> uatomic_sub(&crdp->qlen, cbcount);
> }
> if (uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOP)
> break;
> rcu_thread_offline();
> if (!rt) {
> - if (&crdp->cbs.head
> - == _CMM_LOAD_SHARED(crdp->cbs.tail)) {
> + if (cds_wfq_empty(&crdp->cbs)) {
> call_rcu_wait(crdp);
> poll(NULL, 0, 10);
> uatomic_dec(&crdp->futex);
> @@ -625,32 +617,32 @@ void call_rcu(struct rcu_head *head,
> */
> void call_rcu_data_free(struct call_rcu_data *crdp)
> {
> - struct cds_wfq_node *cbs;
> - struct cds_wfq_node **cbs_tail;
> - struct cds_wfq_node **cbs_endprev;
> -
> if (crdp == NULL || crdp == default_call_rcu_data) {
> return;
> }
> +
> if ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0) {
> uatomic_or(&crdp->flags, URCU_CALL_RCU_STOP);
> wake_call_rcu_thread(crdp);
> while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0)
> poll(NULL, 0, 1);
> }
> - if (&crdp->cbs.head != _CMM_LOAD_SHARED(crdp->cbs.tail)) {
> - while ((cbs = _CMM_LOAD_SHARED(crdp->cbs.head)) == NULL)
> - poll(NULL, 0, 1);
> - _CMM_STORE_SHARED(crdp->cbs.head, NULL);
> - cbs_tail = (struct cds_wfq_node **)
> - uatomic_xchg(&crdp->cbs.tail, &crdp->cbs.head);
> +
> + if (!cds_wfq_empty(&crdp->cbs)) {
> + struct cds_wfq_queue cbs_tmp;
> +
> + cds_wfq_init(&cbs_tmp);
> + __cds_wfq_splice_blocking(&cbs_tmp, &crdp->cbs);
> +
> /* Create default call rcu data if need be */
> (void) get_default_call_rcu_data();
> - cbs_endprev = (struct cds_wfq_node **)
> - uatomic_xchg(&default_call_rcu_data, cbs_tail);
> - *cbs_endprev = cbs;
> +
> + __cds_wfq_splice_blocking(&default_call_rcu_data->cbs,
> + &cbs_tmp);
> +
Too much code to me, cbs_tmp is not required here.
/* Create default call rcu data if need be */
(void) get_default_call_rcu_data();
+ __cds_wfq_splice_blocking(&default_call_rcu_data->cbs,&crdp->cbs);
> uatomic_add(&default_call_rcu_data->qlen,
> uatomic_read(&crdp->qlen));
> +
> wake_call_rcu_thread(default_call_rcu_data);
> }
>
> diff --git a/urcu/static/wfqueue.h b/urcu/static/wfqueue.h
> index 636e1af..08d8d52 100644
> --- a/urcu/static/wfqueue.h
> +++ b/urcu/static/wfqueue.h
> @@ -9,7 +9,8 @@
> * TO BE INCLUDED ONLY IN LGPL-COMPATIBLE CODE. See wfqueue.h for linking
> * dynamically with the userspace rcu library.
> *
> - * Copyright 2010 - Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> + * Copyright 2010-2012 - Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> + * Copyright 2011-2012 - Lai Jiangshan <laijs at cn.fujitsu.com>
> *
> * This library is free software; you can redistribute it and/or
> * modify it under the terms of the GNU Lesser General Public
> @@ -29,6 +30,7 @@
> #include <pthread.h>
> #include <assert.h>
> #include <poll.h>
> +#include <stdbool.h>
> #include <urcu/compiler.h>
> #include <urcu/uatomic.h>
>
> @@ -38,11 +40,16 @@ extern "C" {
>
> /*
> * Queue with wait-free enqueue/blocking dequeue.
> - * This implementation adds a dummy head node when the queue is empty to ensure
> - * we can always update the queue locklessly.
> *
> * Inspired from half-wait-free/half-blocking queue implementation done by
> * Paul E. McKenney.
> + *
> + * Caller must ensure mutual exclusion of queue update operations
> + * "dequeue" and "splice" source queue. Queue read operations "first"
> + * and "next" need to be protected against concurrent "dequeue" and
> + * "splice" (for source queue) by the caller. "enqueue", "splice"
> + * (destination queue), and "empty" are the only operations that can be
> + * used without any mutual exclusion.
> */
>
> #define WFQ_ADAPT_ATTEMPTS 10 /* Retry if being set */
> @@ -57,31 +64,51 @@ static inline void _cds_wfq_init(struct cds_wfq_queue *q)
> {
> int ret;
>
> - _cds_wfq_node_init(&q->dummy);
> /* Set queue head and tail */
> - q->head = &q->dummy;
> - q->tail = &q->dummy.next;
> + _cds_wfq_node_init(&q->head);
> + q->tail = &q->head;
> ret = pthread_mutex_init(&q->lock, NULL);
> assert(!ret);
> }
>
> -static inline void _cds_wfq_enqueue(struct cds_wfq_queue *q,
> - struct cds_wfq_node *node)
> +static inline bool _cds_wfq_empty(struct cds_wfq_queue *q)
> +{
> + /*
> + * Queue is empty if no node is pointed by q->head.next nor q->tail.
> + */
> + return CMM_LOAD_SHARED(q->head.next) == NULL
> + && CMM_LOAD_SHARED(q->tail) == &q->head;
> +}
> +
> +static inline void ___cds_wfq_append(struct cds_wfq_queue *q,
> + struct cds_wfq_node *new_head,
> + struct cds_wfq_node *new_tail)
> {
> - struct cds_wfq_node **old_tail;
> + struct cds_wfq_node *old_tail;
>
> /*
> - * uatomic_xchg() implicit memory barrier orders earlier stores to data
> - * structure containing node and setting node->next to NULL before
> - * publication.
> + * Implicit memory barrier before uatomic_xchg() orders earlier
> + * stores to data structure containing node and setting
> + * node->next to NULL before publication.
> */
> - old_tail = uatomic_xchg(&q->tail, &node->next);
> + old_tail = uatomic_xchg(&q->tail, new_tail);
> +
> /*
> - * At this point, dequeuers see a NULL old_tail->next, which indicates
> - * that the queue is being appended to. The following store will append
> - * "node" to the queue from a dequeuer perspective.
> + * Implicit memory barrier after uatomic_xchg() orders store to
> + * q->tail before store to old_tail->next.
> + *
> + * At this point, dequeuers see a NULL q->tail->next, which
> + * indicates that the queue is being appended to. The following
> + * store will append "node" to the queue from a dequeuer
> + * perspective.
> */
> - CMM_STORE_SHARED(*old_tail, node);
> + CMM_STORE_SHARED(old_tail->next, new_head);
> +}
> +
> +static inline void _cds_wfq_enqueue(struct cds_wfq_queue *q,
> + struct cds_wfq_node *new_tail)
> +{
> + ___cds_wfq_append(q, new_tail, new_tail);
> }
>
> /*
> @@ -100,14 +127,45 @@ ___cds_wfq_node_sync_next(struct cds_wfq_node *node)
> if (++attempt >= WFQ_ADAPT_ATTEMPTS) {
> poll(NULL, 0, WFQ_WAIT); /* Wait for 10ms */
> attempt = 0;
> - } else
> + } else {
> caa_cpu_relax();
> + }
> }
>
> return next;
> }
>
> /*
> + * ___cds_wfq_first_blocking: get first node of a queue, without dequeuing.
> + *
> + * Mutual exclusion with "dequeue" and "splice" operations must be ensured
> + * by the caller.
> + */
> +static inline struct cds_wfq_node *
> +___cds_wfq_first_blocking(struct cds_wfq_queue *q)
> +{
> + if (_cds_wfq_empty(q))
> + return NULL;
> + return ___cds_wfq_node_sync_next(&q->head);
> +}
> +
> +/*
> + * ___cds_wfq_next_blocking: get next node of a queue, without dequeuing.
> + *
> + * Mutual exclusion with "dequeue" and "splice" operations must be ensured
> + * by the caller.
> + */
> +static inline struct cds_wfq_node *
> +___cds_wfq_next_blocking(struct cds_wfq_queue *q, struct cds_wfq_node *node)
> +{
> + if (CMM_LOAD_SHARED(q->tail) == node)
> + return NULL;
> + return ___cds_wfq_node_sync_next(node);
> +}
The same BUG as you told me.
If q has only one node just enqueued by other thread.
but if q->head.next is seen, ___cds_wfq_first_blocking() returns a node,
And the update of q->tail is not seen, it is still &q->head,
___cds_wfq_node_sync_next(node) will be loop for every if there is no
other enqueue.
static inline struct cds_wfq_node *
___cds_wfq_first_blocking(struct cds_wfq_queue *q)
{
+ struct cds_wfq_node *ret.
if (_cds_wfq_empty(q))
return NULL;
ret = ___cds_wfq_node_sync_next(&q->head);
+ cmm_smp_rmb();
+ return ret;
}
> +
> +/*
> + * ___cds_wfq_dequeue_blocking: dequeue a node from the queue.
> + *
> * It is valid to reuse and free a dequeued node immediately.
> *
> * No need to go on a waitqueue here, as there is no possible state in which the
> @@ -120,42 +178,123 @@ ___cds_wfq_dequeue_blocking(struct cds_wfq_queue *q)
> {
> struct cds_wfq_node *node, *next;
>
> - /*
> - * Queue is empty if it only contains the dummy node.
> - */
> - if (q->head == &q->dummy && CMM_LOAD_SHARED(q->tail) == &q->dummy.next)
> + if (_cds_wfq_empty(q))
> return NULL;
> - node = q->head;
>
> - next = ___cds_wfq_node_sync_next(node);
> + node = ___cds_wfq_node_sync_next(&q->head);
> +
> + if ((next = CMM_LOAD_SHARED(node->next)) == NULL) {
> + /* Load node->next before q->tail */
> + cmm_smp_rmb();
> + if (CMM_LOAD_SHARED(q->tail) == node) {
I don't know why I added this "if" since it is likely true.
Could you remove the above 3 lines?
(I remember there is a mb() before uatomic_cmpxchg() which means
this mb() is before the test in uatomic_cmpxchg())
> + /*
> + * @node is the only node in the queue.
> + * Try to move the tail to &q->head
> + */
> + _cds_wfq_node_init(&q->head);
> + if (uatomic_cmpxchg(&q->tail, node, &q->head) == node)
> + return node;
> + }
> + next = ___cds_wfq_node_sync_next(node);
> + }
>
> /*
> * Move queue head forward.
> */
> - q->head = next;
> + q->head.next = next;
> +
> + return node;
> +}
> +
> +/*
> + * ___cds_wfq_splice_blocking: enqueue all src_q nodes at the end of dest_q.
> + *
> + * Dequeue all nodes from src_q.
> + * dest_q must be already initialized.
> + * caller ensures mutual exclusion of dequeue and splice operations on
> + * src_q.
> + */
> +static inline void
> +___cds_wfq_splice_blocking(struct cds_wfq_queue *dest_q,
> + struct cds_wfq_queue *src_q)
> +{
> + struct cds_wfq_node *head, *tail;
> +
> + if (_cds_wfq_empty(src_q))
> + return;
> +
> + head = ___cds_wfq_node_sync_next(&src_q->head);
> + _cds_wfq_node_init(&src_q->head);
> +
> + /*
> + * Memory barrier implied before uatomic_xchg() orders store to
> + * src_q->head before store to src_q->tail. This is required by
> + * concurrent enqueue on src_q, which exchanges the tail before
> + * updating the previous tail's next pointer.
> + */
> + tail = uatomic_xchg(&src_q->tail, &src_q->head);
> +
> /*
> - * Requeue dummy node if we just dequeued it.
> + * Append the spliced content of src_q into dest_q. Does not
> + * require mutual exclusion on dest_q (wait-free).
> */
> - if (node == &q->dummy) {
> - _cds_wfq_node_init(node);
> - _cds_wfq_enqueue(q, node);
> - return ___cds_wfq_dequeue_blocking(q);
> - }
> - return node;
> + ___cds_wfq_append(dest_q, head, tail);
> +}
> +
> +/* Locking performed within cds_wfq calls. */
> +static inline struct cds_wfq_node *
> +_cds_wfq_first_blocking(struct cds_wfq_queue *q)
> +{
> + struct cds_wfq_node *retval;
> + int ret;
> +
> + ret = pthread_mutex_lock(&q->lock);
> + assert(!ret);
> + retval = ___cds_wfq_first_blocking(q);
> + ret = pthread_mutex_unlock(&q->lock);
> + assert(!ret);
> + return retval;
> +}
> +
> +static inline struct cds_wfq_node *
> +_cds_wfq_next_blocking(struct cds_wfq_queue *q, struct cds_wfq_node *node)
> +{
> + struct cds_wfq_node *retval;
> + int ret;
> +
> + ret = pthread_mutex_lock(&q->lock);
> + assert(!ret);
> + retval = ___cds_wfq_next_blocking(q, node);
> + ret = pthread_mutex_unlock(&q->lock);
> + assert(!ret);
> + return retval;
> }
I reject these _cds_wfq_first_blocking(), _cds_wfq_next_blocking()
and cds_wfq_for_each_blocking(), because the claimed "Locking"
makes no sense:
1. It protects nothing in _cds_wfq_next_blocking().
2. There is no "Locking" in the loop body, @node is not dequeued,
it will be invalid if some other dequeue it,
and _cds_wfq_next_blocking() results BUG.
>
> static inline struct cds_wfq_node *
> _cds_wfq_dequeue_blocking(struct cds_wfq_queue *q)
> {
> - struct cds_wfq_node *retnode;
> + struct cds_wfq_node *retval;
> int ret;
>
> ret = pthread_mutex_lock(&q->lock);
> assert(!ret);
> - retnode = ___cds_wfq_dequeue_blocking(q);
> + retval = ___cds_wfq_dequeue_blocking(q);
> ret = pthread_mutex_unlock(&q->lock);
> assert(!ret);
> - return retnode;
> + return retval;
> +}
> +
> +static inline void
> +_cds_wfq_splice_blocking(struct cds_wfq_queue *dest_q,
> + struct cds_wfq_queue *src_q)
> +{
> + int ret;
> +
> + ret = pthread_mutex_lock(&src_q->lock);
> + assert(!ret);
> + ___cds_wfq_splice_blocking(dest_q, src_q);
> + ret = pthread_mutex_unlock(&src_q->lock);
> + assert(!ret);
> }
>
> #ifdef __cplusplus
> diff --git a/urcu/wfqueue.h b/urcu/wfqueue.h
> index 03a73f1..d33d47a 100644
> --- a/urcu/wfqueue.h
> +++ b/urcu/wfqueue.h
> @@ -6,7 +6,8 @@
> *
> * Userspace RCU library - Queue with Wait-Free Enqueue/Blocking Dequeue
> *
> - * Copyright 2010 - Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> + * Copyright 2010-2012 - Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> + * Copyright 2011-2012 - Lai Jiangshan <laijs at cn.fujitsu.com>
> *
> * This library is free software; you can redistribute it and/or
> * modify it under the terms of the GNU Lesser General Public
> @@ -25,6 +26,7 @@
>
> #include <pthread.h>
> #include <assert.h>
> +#include <stdbool.h>
> #include <urcu/compiler.h>
>
> #ifdef __cplusplus
> @@ -33,8 +35,6 @@ extern "C" {
>
> /*
> * Queue with wait-free enqueue/blocking dequeue.
> - * This implementation adds a dummy head node when the queue is empty to ensure
> - * we can always update the queue locklessly.
> *
> * Inspired from half-wait-free/half-blocking queue implementation done by
> * Paul E. McKenney.
> @@ -45,8 +45,8 @@ struct cds_wfq_node {
> };
>
> struct cds_wfq_queue {
> - struct cds_wfq_node *head, **tail;
> - struct cds_wfq_node dummy; /* Dummy node */
> + struct cds_wfq_node head, *tail;
> + struct cds_wfq_node padding; /* unused */
> pthread_mutex_t lock;
> };
Why keep the padding?
>
> @@ -55,22 +55,90 @@ struct cds_wfq_queue {
> #include <urcu/static/wfqueue.h>
>
> #define cds_wfq_node_init _cds_wfq_node_init
> -#define cds_wfq_init _cds_wfq_init
> -#define cds_wfq_enqueue _cds_wfq_enqueue
> -#define __cds_wfq_dequeue_blocking ___cds_wfq_dequeue_blocking
> +#define cds_wfq_init _cds_wfq_init
> +#define cds_wfq_empty _cds_wfq_empty
> +#define cds_wfq_enqueue _cds_wfq_enqueue
> +
> +/* Locking performed within cds_wfq calls. */
> #define cds_wfq_dequeue_blocking _cds_wfq_dequeue_blocking
> +#define cds_wfq_splice_blocking _cds_wfq_splice_blocking
> +#define cds_wfq_first_blocking _cds_wfq_first_blocking
> +#define cds_wfq_next_blocking _cds_wfq_next_blocking
> +
> +/* Locking ensured by caller */
> +#define __cds_wfq_dequeue_blocking ___cds_wfq_dequeue_blocking
> +#define __cds_wfq_splice_blocking ___cds_wfq_splice_blocking
> +#define __cds_wfq_first_blocking ___cds_wfq_first_blocking
> +#define __cds_wfq_next_blocking ___cds_wfq_next_blocking
>
> #else /* !_LGPL_SOURCE */
>
> extern void cds_wfq_node_init(struct cds_wfq_node *node);
> extern void cds_wfq_init(struct cds_wfq_queue *q);
> +extern bool cds_wfq_empty(struct cds_wfq_queue *q);
> extern void cds_wfq_enqueue(struct cds_wfq_queue *q, struct cds_wfq_node *node);
> -/* __cds_wfq_dequeue_blocking: caller ensures mutual exclusion between dequeues */
> -extern struct cds_wfq_node *__cds_wfq_dequeue_blocking(struct cds_wfq_queue *q);
> +
> +/* Locking performed within cds_wfq calls. */
> extern struct cds_wfq_node *cds_wfq_dequeue_blocking(struct cds_wfq_queue *q);
> +extern void cds_wfq_splice_blocking(struct cds_wfq_queue *dest_q,
> + struct cds_wfq_queue *src_q);
> +extern struct cds_wfq_node *cds_wfq_first_blocking(struct cds_wfq_queue *q);
> +extern struct cds_wfq_node *cds_wfq_next_blocking(struct cds_wfq_queue *q,
> + struct cds_wfq_node *node);
> +
> +/*
> + * __cds_wfq_dequeue_blocking: caller ensures mutual exclusion of dequeue
> + * and splice operations.
> + */
> +extern struct cds_wfq_node *__cds_wfq_dequeue_blocking(struct cds_wfq_queue *q);
> +
> +/*
> + * __cds_wfq_splice_blocking: caller ensures mutual exclusion of dequeue and
> + * splice operations on src_q. dest_q must be already initialized.
> + */
> +extern void __cds_wfq_splice_blocking(struct cds_wfq_queue *dest_q,
> + struct cds_wfq_queue *src_q);
> +
> +/*
> + * __cds_wfq_first_blocking: mutual exclusion with "dequeue" and
> + * "splice" operations must be ensured by the caller.
> + */
> +extern struct cds_wfq_node *__cds_wfq_first_blocking(struct cds_wfq_queue *q);
> +
> +/*
> + * __cds_wfq_next_blocking: mutual exclusion with "dequeue" and "splice"
> + * operations must be ensured by the caller.
> + */
> +extern struct cds_wfq_node *__cds_wfq_next_blocking(struct cds_wfq_queue *q,
> + struct cds_wfq_node *node);
>
> #endif /* !_LGPL_SOURCE */
>
> +/*
> + * cds_wfq_for_each_blocking: Iterate over all nodes in a queue, without
> + * dequeuing them.
> + *
> + * cds_wfq_for_each_blocking: mutual exclusion is performed within the
> + * cds_wfq calls.
> + */
> +#define cds_wfq_for_each_blocking(q, node) \
> + for (node = cds_wfq_first_blocking(q); \
> + node != NULL; \
> + node = cds_wfq_next_blocking(q, node))
> +
> +/*
> + * __cds_wfq_for_each_blocking: Iterate over all nodes in a queue,
> + * without dequeuing them.
> + *
> + * Mutual exclusion with "dequeue" and "splice" operations must be
> + * ensured by the caller.
> + */
> +
> +#define __cds_wfq_for_each_blocking(q, node) \
> + for (node = __cds_wfq_first_blocking(q); \
> + node != NULL; \
> + node = __cds_wfq_next_blocking(q, node))
> +
> #ifdef __cplusplus
> }
> #endif
> diff --git a/wfqueue.c b/wfqueue.c
> index 3337171..cf3dae6 100644
> --- a/wfqueue.c
> +++ b/wfqueue.c
> @@ -3,7 +3,8 @@
> *
> * Userspace RCU library - Queue with Wait-Free Enqueue/Blocking Dequeue
> *
> - * Copyright 2010 - Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> + * Copyright 2010-2012 - Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> + * Copyright 2011-2012 - Lai Jiangshan <laijs at cn.fujitsu.com>
> *
> * This library is free software; you can redistribute it and/or
> * modify it under the terms of the GNU Lesser General Public
> @@ -38,17 +39,56 @@ void cds_wfq_init(struct cds_wfq_queue *q)
> _cds_wfq_init(q);
> }
>
> +bool cds_wfq_empty(struct cds_wfq_queue *q)
> +{
> + return _cds_wfq_empty(q);
> +}
> +
> void cds_wfq_enqueue(struct cds_wfq_queue *q, struct cds_wfq_node *node)
> {
> _cds_wfq_enqueue(q, node);
> }
>
> +struct cds_wfq_node *cds_wfq_dequeue_blocking(struct cds_wfq_queue *q)
> +{
> + return _cds_wfq_dequeue_blocking(q);
> +}
> +
> +void cds_wfq_splice_blocking(struct cds_wfq_queue *dest_q,
> + struct cds_wfq_queue *src_q)
> +{
> + _cds_wfq_splice_blocking(dest_q, src_q);
> +}
> +
> +struct cds_wfq_node *cds_wfq_first_blocking(struct cds_wfq_queue *q)
> +{
> + return _cds_wfq_first_blocking(q);
> +}
> +
> +struct cds_wfq_node *cds_wfq_next_blocking(struct cds_wfq_queue *q,
> + struct cds_wfq_node *node)
> +{
> + return _cds_wfq_next_blocking(q, node);
> +}
> +
> struct cds_wfq_node *__cds_wfq_dequeue_blocking(struct cds_wfq_queue *q)
> {
> return ___cds_wfq_dequeue_blocking(q);
> }
>
> -struct cds_wfq_node *cds_wfq_dequeue_blocking(struct cds_wfq_queue *q)
> +void __cds_wfq_splice_blocking(struct cds_wfq_queue *dest_q,
> + struct cds_wfq_queue *src_q)
> {
> - return _cds_wfq_dequeue_blocking(q);
> + ___cds_wfq_splice_blocking(dest_q, src_q);
> +}
> +
> +struct cds_wfq_node *__cds_wfq_first_blocking(struct cds_wfq_queue *q)
> +{
> + return ___cds_wfq_first_blocking(q);
> +}
> +
> +struct cds_wfq_node *__cds_wfq_next_blocking(struct cds_wfq_queue *q,
> + struct cds_wfq_node *node)
> +{
> + return ___cds_wfq_next_blocking(q, node);
> }
>
> --
> Mathieu Desnoyers
> Operating System Efficiency R&D Consultant
> EfficiOS Inc.
> http://www.efficios.com
Thanks,
Lai
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