src/queue.c

/*
 * Queue management functions.
 *
 * Copyright 2000-2009 Willy Tarreau <w@1wt.eu>
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version
 * 2 of the License, or (at your option) any later version.
 *
 */

/* Short explanation on the locking, which is far from being trivial : a
 * pendconn is a list element which necessarily is associated with an existing
 * stream. It has pendconn->strm always valid. A pendconn may only be in one of
 * these three states :
 *   - unlinked : in this case it is an empty list head ;
 *   - linked into the server's queue ;
 *   - linked into the proxy's queue.
 *
 * A stream does not necessarily have such a pendconn. Thus the pendconn is
 * designated by the stream->pend_pos pointer. This results in some properties :
 *   - pendconn->strm->pend_pos is never NULL for any valid pendconn
 *   - if p->node.node.leaf_p is NULL, the element is unlinked,
 *     otherwise it necessarily belongs to one of the other lists ; this may
 *     not be atomically checked under threads though ;
 *   - pendconn->px is never NULL if pendconn->list is not empty
 *   - pendconn->srv is never NULL if pendconn->list is in the server's queue,
 *     and is always NULL if pendconn->list is in the backend's queue or empty.
 *   - pendconn->target is NULL while the element is queued, and points to the
 *     assigned server when the pendconn is picked.
 *
 * Threads complicate the design a little bit but rules remain simple :
 *   - the server's queue lock must be held at least when manipulating the
 *     server's queue, which is when adding a pendconn to the queue and when
 *     removing a pendconn from the queue. It protects the queue's integrity.
 *
 *   - the proxy's queue lock must be held at least when manipulating the
 *     proxy's queue, which is when adding a pendconn to the queue and when
 *     removing a pendconn from the queue. It protects the queue's integrity.
 *
 *   - both locks are compatible and may be held at the same time.
 *
 *   - a pendconn_add() is only performed by the stream which will own the
 *     pendconn ; the pendconn is allocated at this moment and returned ; it is
 *     added to either the server or the proxy's queue while holding this
s *     queue's lock.
 *
 *   - the pendconn is then met by a thread walking over the proxy or server's
 *     queue with the respective lock held. This lock is exclusive and the
 *     pendconn can only appear in one queue so by definition a single thread
 *     may find this pendconn at a time.
 *
 *   - the pendconn is unlinked either by its own stream upon success/abort/
 *     free, or by another one offering it its server slot. This is achieved by
 *     pendconn_process_next_strm() under either the server or proxy's lock,
 *     pendconn_redistribute() under the server's lock, pendconn_grab_from_px()
 *     under the proxy's lock, or pendconn_unlink() under either the proxy's or
 *     the server's lock depending on the queue the pendconn is attached to.
 *
 *   - no single operation except the pendconn initialisation prior to the
 *     insertion are performed without eithre a queue lock held or the element
 *     being unlinked and visible exclusively to its stream.
 *
 *   - pendconn_grab_from_px() and pendconn_process_next_strm() assign ->target
 *     so that the stream knows what server to work with (via
 *     pendconn_dequeue() which sets it on strm->target).
 *
 *   - a pendconn doesn't switch between queues, it stays where it is.
 */

#include <import/eb32tree.h>
#include <haproxy/api.h>
#include <haproxy/backend.h>
#include <haproxy/http_rules.h>
#include <haproxy/pool.h>
#include <haproxy/queue.h>
#include <haproxy/sample.h>
#include <haproxy/server-t.h>
#include <haproxy/stream.h>
#include <haproxy/task.h>
#include <haproxy/tcp_rules.h>
#include <haproxy/thread.h>
#include <haproxy/time.h>
#include <haproxy/tools.h>


#define NOW_OFFSET_BOUNDARY()          ((now_ms - (TIMER_LOOK_BACK >> 12)) & 0xfffff)
#define KEY_CLASS(key)                 ((u32)key & 0xfff00000)
#define KEY_OFFSET(key)                ((u32)key & 0x000fffff)
#define KEY_CLASS_OFFSET_BOUNDARY(key) (KEY_CLASS(key) | NOW_OFFSET_BOUNDARY())
#define MAKE_KEY(class, offset)        (((u32)(class + 0x7ff) << 20) | ((u32)(now_ms + offset) & 0xfffff))

DECLARE_POOL(pool_head_pendconn, "pendconn", sizeof(struct pendconn));

/* returns the effective dynamic maxconn for a server, considering the minconn
 * and the proxy's usage relative to its dynamic connections limit. It is
 * expected that 0 < s->minconn <= s->maxconn when this is called. If the
 * server is currently warming up, the slowstart is also applied to the
 * resulting value, which can be lower than minconn in this case, but never
 * less than 1.
 */
unsigned int srv_dynamic_maxconn(const struct server *s)
{
	unsigned int max;

	if (s->proxy->beconn >= s->proxy->fullconn)
		/* no fullconn or proxy is full */
		max = s->maxconn;
	else if (s->minconn == s->maxconn)
		/* static limit */
		max = s->maxconn;
	else max = MAX(s->minconn,
		       s->proxy->beconn * s->maxconn / s->proxy->fullconn);

	if ((s->cur_state == SRV_ST_STARTING) &&
	    ns_to_sec(now_ns) < s->last_change + s->slowstart &&
	    ns_to_sec(now_ns) >= s->last_change) {
		unsigned int ratio;
		ratio = 100 * (ns_to_sec(now_ns) - s->last_change) / s->slowstart;
		max = MAX(1, max * ratio / 100);
	}
	return max;
}

/* Remove the pendconn from the server's queue. At this stage, the connection
 * is not really dequeued. It will be done during the process_stream. It is
 * up to the caller to atomically decrement the pending counts.
 *
 * The caller must own the lock on the server queue. The pendconn must still be
 * queued (p->node.leaf_p != NULL) and must be in a server (p->srv != NULL).
 */
static void __pendconn_unlink_srv(struct pendconn *p)
{
	p->strm->logs.srv_queue_pos += _HA_ATOMIC_LOAD(&p->queue->idx) - p->queue_idx;
	eb32_delete(&p->node);
}

/* Remove the pendconn from the proxy's queue. At this stage, the connection
 * is not really dequeued. It will be done during the process_stream. It is
 * up to the caller to atomically decrement the pending counts.
 *
 * The caller must own the lock on the proxy queue. The pendconn must still be
 * queued (p->node.leaf_p != NULL) and must be in the proxy (p->srv == NULL).
 */
static void __pendconn_unlink_prx(struct pendconn *p)
{
	p->strm->logs.prx_queue_pos += _HA_ATOMIC_LOAD(&p->queue->idx) - p->queue_idx;
	eb32_delete(&p->node);
}

/* Locks the queue the pendconn element belongs to. This relies on both p->px
 * and p->srv to be properly initialized (which is always the case once the
 * element has been added).
 */
static inline void pendconn_queue_lock(struct pendconn *p)
{
	HA_SPIN_LOCK(QUEUE_LOCK, &p->queue->lock);
}

/* Unlocks the queue the pendconn element belongs to. This relies on both p->px
 * and p->srv to be properly initialized (which is always the case once the
 * element has been added).
 */
static inline void pendconn_queue_unlock(struct pendconn *p)
{
	HA_SPIN_UNLOCK(QUEUE_LOCK, &p->queue->lock);
}

/* Removes the pendconn from the server/proxy queue. At this stage, the
 * connection is not really dequeued. It will be done during process_stream().
 * This function takes all the required locks for the operation. The pendconn
 * must be valid, though it doesn't matter if it was already unlinked. Prefer
 * pendconn_cond_unlink() to first check <p>. It also forces a serialization
 * on p->del_lock to make sure another thread currently waking it up finishes
 * first.
 */
void pendconn_unlink(struct pendconn *p)
{
	struct queue  *q  = p->queue;
	struct proxy  *px = q->px;
	struct server *sv = q->sv;
	uint oldidx;
	int done = 0;

	oldidx = _HA_ATOMIC_LOAD(&p->queue->idx);
	HA_SPIN_LOCK(QUEUE_LOCK, &q->lock);
	HA_SPIN_LOCK(QUEUE_LOCK, &p->del_lock);

	if (p->node.node.leaf_p) {
		eb32_delete(&p->node);
		done = 1;
	}

	HA_SPIN_UNLOCK(QUEUE_LOCK, &p->del_lock);
	HA_SPIN_UNLOCK(QUEUE_LOCK, &q->lock);

	if (done) {
		oldidx -= p->queue_idx;
		if (sv)
			p->strm->logs.srv_queue_pos += oldidx;
		else
			p->strm->logs.prx_queue_pos += oldidx;

		_HA_ATOMIC_DEC(&q->length);
		_HA_ATOMIC_DEC(&px->totpend);
	}
}

/* Retrieve the first pendconn from tree <pendconns>. Classes are always
 * considered first, then the time offset. The time does wrap, so the
 * lookup is performed twice, one to retrieve the first class and a second
 * time to retrieve the earliest time in this class.
 */
static struct pendconn *pendconn_first(struct eb_root *pendconns)
{
	struct eb32_node *node, *node2 = NULL;
	u32 key;

	node = eb32_first(pendconns);
	if (!node)
		return NULL;

	key = KEY_CLASS_OFFSET_BOUNDARY(node->key);
	node2 = eb32_lookup_ge(pendconns, key);

	if (!node2 ||
	    KEY_CLASS(node2->key) != KEY_CLASS(node->key)) {
		/* no other key in the tree, or in this class */
		return eb32_entry(node, struct pendconn, node);
	}

	/* found a better key */
	return eb32_entry(node2, struct pendconn, node);
}

/* Process the next pending connection from either a server or a proxy, and
 * returns a strictly positive value on success (see below). If no pending
 * connection is found, 0 is returned.  Note that neither <srv> nor <px> may be
 * NULL.  Priority is given to the oldest request in the queue if both <srv> and
 * <px> have pending requests. This ensures that no request will be left
 * unserved.  The <px> queue is not considered if the server (or a tracked
 * server) is not RUNNING, is disabled, or has a null weight (server going
 * down). The <srv> queue is still considered in this case, because if some
 * connections remain there, it means that some requests have been forced there
 * after it was seen down (eg: due to option persist).  The stream is
 * immediately marked as "assigned", and both its <srv> and <srv_conn> are set
 * to <srv>.
 *
 * The proxy's queue will be consulted only if px_ok is non-zero.
 *
 * This function must only be called if the server queue is locked _AND_ the
 * proxy queue is not. Today it is only called by process_srv_queue.
 * When a pending connection is dequeued, this function returns 1 if a pendconn
 * is dequeued, otherwise 0.
 */
static int pendconn_process_next_strm(struct server *srv, struct proxy *px, int px_ok)
{
	struct pendconn *p = NULL;
	struct pendconn *pp = NULL;
	u32 pkey, ppkey;

	p = NULL;
	if (srv->queue.length)
		p = pendconn_first(&srv->queue.head);

	pp = NULL;
	if (px_ok && px->queue.length) {
		/* the lock only remains held as long as the pp is
		 * in the proxy's queue.
		 */
		HA_SPIN_LOCK(QUEUE_LOCK,  &px->queue.lock);
		pp = pendconn_first(&px->queue.head);
		if (!pp)
			HA_SPIN_UNLOCK(QUEUE_LOCK,  &px->queue.lock);
	}

	if (!p && !pp)
		return 0;
	else if (!pp)
		goto use_p; /*  p != NULL */
	else if (!p)
		goto use_pp; /* pp != NULL */

	/* p != NULL && pp != NULL*/

	if (KEY_CLASS(p->node.key) < KEY_CLASS(pp->node.key))
		goto use_p;

	if (KEY_CLASS(pp->node.key) < KEY_CLASS(p->node.key))
		goto use_pp;

	pkey  = KEY_OFFSET(p->node.key);
	ppkey = KEY_OFFSET(pp->node.key);

	if (pkey < NOW_OFFSET_BOUNDARY())
		pkey += 0x100000; // key in the future

	if (ppkey < NOW_OFFSET_BOUNDARY())
		ppkey += 0x100000; // key in the future

	if (pkey <= ppkey)
		goto use_p;

 use_pp:
	/* we'd like to release the proxy lock ASAP to let other threads
	 * work with other servers. But for this we must first hold the
	 * pendconn alive to prevent a removal from its owning stream.
	 */
	HA_SPIN_LOCK(QUEUE_LOCK, &pp->del_lock);

	/* now the element won't go, we can release the proxy */
	__pendconn_unlink_prx(pp);
	HA_SPIN_UNLOCK(QUEUE_LOCK, &px->queue.lock);

	pp->strm_flags |= SF_ASSIGNED;
	pp->target = srv;
	stream_add_srv_conn(pp->strm, srv);

	/* we must wake the task up before releasing the lock as it's the only
	 * way to make sure the task still exists. The pendconn cannot vanish
	 * under us since the task will need to take the lock anyway and to wait
	 * if it wakes up on a different thread.
	 */
	task_wakeup(pp->strm->task, TASK_WOKEN_RES);
	HA_SPIN_UNLOCK(QUEUE_LOCK, &pp->del_lock);

	_HA_ATOMIC_DEC(&px->queue.length);
	_HA_ATOMIC_INC(&px->queue.idx);
	return 1;

 use_p:
	/* we don't need the px queue lock anymore, we have the server's lock */
	if (pp)
		HA_SPIN_UNLOCK(QUEUE_LOCK, &px->queue.lock);

	p->strm_flags |= SF_ASSIGNED;
	p->target = srv;
	stream_add_srv_conn(p->strm, srv);

	/* we must wake the task up before releasing the lock as it's the only
	 * way to make sure the task still exists. The pendconn cannot vanish
	 * under us since the task will need to take the lock anyway and to wait
	 * if it wakes up on a different thread.
	 */
	task_wakeup(p->strm->task, TASK_WOKEN_RES);
	__pendconn_unlink_srv(p);

	_HA_ATOMIC_DEC(&srv->queue.length);
	_HA_ATOMIC_INC(&srv->queue.idx);
	return 1;
}

/* Manages a server's connection queue. This function will try to dequeue as
 * many pending streams as possible, and wake them up.
 */
void process_srv_queue(struct server *s)
{
	struct server *ref = s->track ? s->track : s;
	struct proxy  *p = s->proxy;
	int maxconn;
	int stop = 0;
	int done = 0;
	int px_ok;

	/* if a server is not usable or backup and must not be used
	 * to dequeue backend requests.
	 */
	px_ok = srv_currently_usable(ref) &&
	        (!(s->flags & SRV_F_BACKUP) ||
	         (!p->srv_act &&
	          (s == p->lbprm.fbck || (p->options & PR_O_USE_ALL_BK))));

	/* let's repeat that under the lock on each round. Threads competing
	 * for the same server will give up, knowing that at least one of
	 * them will check the conditions again before quitting. In order
	 * to avoid the deadly situation where one thread spends its time
	 * dequeueing for others, we limit the number of rounds it does.
	 * However we still re-enter the loop for one pass if there's no
	 * more served, otherwise we could end up with no other thread
	 * trying to dequeue them.
	 *
	 * There's one racy part: we don't want to have more than one thread
	 * in charge of dequeuing, hence the dequeung flag. We cannot rely
	 * on a trylock here because it would compete against pendconn_add()
	 * and would occasionally leave entries in the queue that are never
	 * dequeued. Nobody else uses the dequeuing flag so when seeing it
	 * non-null, we're certain that another thread is waiting on it.
	 */
	while (!stop && (done < global.tune.maxpollevents || !s->served) &&
	       s->served < (maxconn = srv_dynamic_maxconn(s))) {
		if (HA_ATOMIC_XCHG(&s->dequeuing, 1))
			break;

		HA_SPIN_LOCK(QUEUE_LOCK, &s->queue.lock);
		while (s->served < maxconn) {
			stop = !pendconn_process_next_strm(s, p, px_ok);
			if (stop)
				break;
			_HA_ATOMIC_INC(&s->served);
			done++;
			if (done >= global.tune.maxpollevents)
				break;
		}
		HA_ATOMIC_STORE(&s->dequeuing, 0);
		HA_SPIN_UNLOCK(QUEUE_LOCK, &s->queue.lock);
	}

	if (done) {
		_HA_ATOMIC_SUB(&p->totpend, done);
		_HA_ATOMIC_ADD(&p->served, done);
		__ha_barrier_atomic_store();
		if (p->lbprm.server_take_conn)
			p->lbprm.server_take_conn(s);
	}
}

/* Adds the stream <strm> to the pending connection queue of server <strm>->srv
 * or to the one of <strm>->proxy if srv is NULL. All counters and back pointers
 * are updated accordingly. Returns NULL if no memory is available, otherwise the
 * pendconn itself. If the stream was already marked as served, its flag is
 * cleared. It is illegal to call this function with a non-NULL strm->srv_conn.
 * The stream's queue position is counted with an offset of -1 because we want
 * to make sure that being at the first position in the queue reports 1.
 *
 * The queue is sorted by the composition of the priority_class, and the current
 * timestamp offset by strm->priority_offset. The timestamp is in milliseconds
 * and truncated to 20 bits, so will wrap every 17m28s575ms.
 * The offset can be positive or negative, and an offset of 0 puts it in the
 * middle of this range (~ 8 min). Note that this also means if the adjusted
 * timestamp wraps around, the request will be misinterpreted as being of
 * the highest priority for that priority class.
 *
 * This function must be called by the stream itself, so in the context of
 * process_stream.
 */
struct pendconn *pendconn_add(struct stream *strm)
{
	struct pendconn *p;
	struct proxy    *px;
	struct server   *srv;
	struct queue    *q;
	unsigned int *max_ptr;
	unsigned int old_max, new_max;

	p = pool_alloc(pool_head_pendconn);
	if (!p)
		return NULL;

	p->target     = NULL;
	p->node.key   = MAKE_KEY(strm->priority_class, strm->priority_offset);
	p->strm       = strm;
	p->strm_flags = strm->flags;
	HA_SPIN_INIT(&p->del_lock);
	strm->pend_pos = p;

	px = strm->be;
	if (strm->flags & SF_ASSIGNED)
		srv = objt_server(strm->target);
	else
		srv = NULL;

	if (srv) {
		q = &srv->queue;
		max_ptr = &srv->counters.nbpend_max;
	}
	else {
		q = &px->queue;
		max_ptr = &px->be_counters.nbpend_max;
	}

	p->queue = q;
	p->queue_idx  = _HA_ATOMIC_LOAD(&q->idx) - 1; // for logging only
	new_max = _HA_ATOMIC_ADD_FETCH(&q->length, 1);
	old_max = _HA_ATOMIC_LOAD(max_ptr);
	while (new_max > old_max) {
		if (likely(_HA_ATOMIC_CAS(max_ptr, &old_max, new_max)))
			break;
	}
	__ha_barrier_atomic_store();

	HA_SPIN_LOCK(QUEUE_LOCK, &q->lock);
	eb32_insert(&q->head, &p->node);
	HA_SPIN_UNLOCK(QUEUE_LOCK, &q->lock);

	_HA_ATOMIC_INC(&px->totpend);
	return p;
}

/* Redistribute pending connections when a server goes down. The number of
 * connections redistributed is returned. It will take the server queue lock
 * and does not use nor depend on other locks.
 */
int pendconn_redistribute(struct server *s)
{
	struct pendconn *p;
	struct eb32_node *node, *nodeb;
	int xferred = 0;

	/* The REDISP option was specified. We will ignore cookie and force to
	 * balance or use the dispatcher. */
	if ((s->proxy->options & (PR_O_REDISP|PR_O_PERSIST)) != PR_O_REDISP)
		return 0;

	HA_SPIN_LOCK(QUEUE_LOCK, &s->queue.lock);
	for (node = eb32_first(&s->queue.head); node; node = nodeb) {
		nodeb =	eb32_next(node);

		p = eb32_entry(node, struct pendconn, node);
		if (p->strm_flags & SF_FORCE_PRST)
			continue;

		/* it's left to the dispatcher to choose a server */
		__pendconn_unlink_srv(p);
		p->strm_flags &= ~(SF_DIRECT | SF_ASSIGNED);

		task_wakeup(p->strm->task, TASK_WOKEN_RES);
		xferred++;
	}
	HA_SPIN_UNLOCK(QUEUE_LOCK, &s->queue.lock);

	if (xferred) {
		_HA_ATOMIC_SUB(&s->queue.length, xferred);
		_HA_ATOMIC_SUB(&s->proxy->totpend, xferred);
	}
	return xferred;
}

/* Check for pending connections at the backend, and assign some of them to
 * the server coming up. The server's weight is checked before being assigned
 * connections it may not be able to handle. The total number of transferred
 * connections is returned. It will take the proxy's queue lock and will not
 * use nor depend on other locks.
 */
int pendconn_grab_from_px(struct server *s)
{
	struct pendconn *p;
	int maxconn, xferred = 0;

	if (!srv_currently_usable(s))
		return 0;

	/* if this is a backup server and there are active servers or at
	 * least another backup server was elected, then this one must
	 * not dequeue requests from the proxy.
	 */
	if ((s->flags & SRV_F_BACKUP) &&
	    (s->proxy->srv_act ||
	     ((s != s->proxy->lbprm.fbck) && !(s->proxy->options & PR_O_USE_ALL_BK))))
		return 0;

	HA_SPIN_LOCK(QUEUE_LOCK, &s->proxy->queue.lock);
	maxconn = srv_dynamic_maxconn(s);
	while ((p = pendconn_first(&s->proxy->queue.head))) {
		if (s->maxconn && s->served + xferred >= maxconn)
			break;

		__pendconn_unlink_prx(p);
		p->target = s;

		task_wakeup(p->strm->task, TASK_WOKEN_RES);
		xferred++;
	}
	HA_SPIN_UNLOCK(QUEUE_LOCK, &s->proxy->queue.lock);
	if (xferred) {
		_HA_ATOMIC_SUB(&s->proxy->queue.length, xferred);
		_HA_ATOMIC_SUB(&s->proxy->totpend, xferred);
	}
	return xferred;
}

/* Try to dequeue pending connection attached to the stream <strm>. It must
 * always exists here. If the pendconn is still linked to the server or the
 * proxy queue, nothing is done and the function returns 1. Otherwise,
 * <strm>->flags and <strm>->target are updated, the pendconn is released and 0
 * is returned.
 *
 * This function must be called by the stream itself, so in the context of
 * process_stream.
 */
int pendconn_dequeue(struct stream *strm)
{
	struct pendconn *p;
	int is_unlinked;

	/* unexpected case because it is called by the stream itself and
	 * only the stream can release a pendconn. So it is only
	 * possible if a pendconn is released by someone else or if the
	 * stream is supposed to be queued but without its associated
	 * pendconn. In both cases it is a bug! */
	BUG_ON(!strm->pend_pos);

	p = strm->pend_pos;

	/* note below : we need to grab the queue's lock to check for emptiness
	 * because we don't want a partial _grab_from_px() or _redistribute()
	 * to be called in parallel and show an empty list without having the
	 * time to finish. With this we know that if we see the element
	 * unlinked, these functions were completely done.
	 */
	pendconn_queue_lock(p);
	is_unlinked = !p->node.node.leaf_p;
	pendconn_queue_unlock(p);

	/* serialize to make sure the element was finished processing */
	HA_SPIN_LOCK(QUEUE_LOCK, &p->del_lock);
	HA_SPIN_UNLOCK(QUEUE_LOCK, &p->del_lock);

	if (!is_unlinked)
		return 1;

	/* the pendconn is not queued anymore and will not be so we're safe
	 * to proceed.
	 */
	strm->flags &= ~(SF_DIRECT | SF_ASSIGNED);
	strm->flags |= p->strm_flags & (SF_DIRECT | SF_ASSIGNED);

	/* the entry might have been redistributed to another server */
	if (!(strm->flags & SF_ASSIGNED))
		sockaddr_free(&strm->scb->dst);

	if (p->target) {
		/* a server picked this pendconn, it must skip LB */
		strm->target = &p->target->obj_type;
		strm->flags |= SF_ASSIGNED;
	}

	strm->pend_pos = NULL;
	pool_free(pool_head_pendconn, p);
	return 0;
}

/* checks after a successful pendconn_add() if the connection ended up being
 * alone with no active connection left to dequeue it. In such a case it will
 * simply remove it from the queue, free it and return non-zero to inform the
 * caller that it must try to add the connection again, otherwise it returns
 * zero, indicating that the connection will be handled normally. The caller
 * might have to drop SF_DIRECT and/or SF_ASSIGNED if the conn was on a proxy.
 */
int pendconn_must_try_again(struct pendconn *p)
{
	struct queue  *q  = p->queue;
	struct proxy  *px = q->px;
	struct server *sv = q->sv;
	int ret = 0;

	if (likely(!HA_ATOMIC_LOAD(&p->node.node.leaf_p)))
		goto leave;

	/* for a server, we need at least one conn left on this server to
	 * find ours.
	 */
	if (likely(sv && HA_ATOMIC_LOAD(&sv->served)))
		goto leave;

	/* for a backend, we need at least one conn left on any of this
	 * backend's servers to find ours.
	 */
	if (likely(!sv && HA_ATOMIC_LOAD(&px->served)))
		goto leave;

	/* OK the situation is not safe anymore, we need to check if we're
	 * still in the queue under a lock.
	 */
	HA_SPIN_LOCK(QUEUE_LOCK, &q->lock);
	HA_SPIN_LOCK(QUEUE_LOCK, &p->del_lock);

	if (p->node.node.leaf_p) {
		eb32_delete(&p->node);
		_HA_ATOMIC_DEC(&q->length);
		_HA_ATOMIC_INC(&q->idx);
		_HA_ATOMIC_DEC(&px->totpend);
		ret = 1;
	}

	HA_SPIN_UNLOCK(QUEUE_LOCK, &p->del_lock);
	HA_SPIN_UNLOCK(QUEUE_LOCK, &q->lock);

	/* check if the connection was still queued. If not, it means its
	 * processing has begun so it's safe.
	 */
	if (!ret)
		goto leave;

	/* The pendconn is not queued anymore and will not be so we're safe
	 * to free it.
	 */
	p->strm->pend_pos = NULL;
	pool_free(pool_head_pendconn, p);

leave:
	return ret;
}

static enum act_return action_set_priority_class(struct act_rule *rule, struct proxy *px,
                                                 struct session *sess, struct stream *s, int flags)
{
	struct sample *smp;

	smp = sample_fetch_as_type(px, sess, s, SMP_OPT_DIR_REQ|SMP_OPT_FINAL, rule->arg.expr, SMP_T_SINT);
	if (!smp)
		return ACT_RET_CONT;

	s->priority_class = queue_limit_class(smp->data.u.sint);
	return ACT_RET_CONT;
}

static enum act_return action_set_priority_offset(struct act_rule *rule, struct proxy *px,
                                                  struct session *sess, struct stream *s, int flags)
{
	struct sample *smp;

	smp = sample_fetch_as_type(px, sess, s, SMP_OPT_DIR_REQ|SMP_OPT_FINAL, rule->arg.expr, SMP_T_SINT);
	if (!smp)
		return ACT_RET_CONT;

	s->priority_offset = queue_limit_offset(smp->data.u.sint);

	return ACT_RET_CONT;
}

static enum act_parse_ret parse_set_priority_class(const char **args, int *arg, struct proxy *px,
                                                   struct act_rule *rule, char **err)
{
	unsigned int where = 0;

	rule->arg.expr = sample_parse_expr((char **)args, arg, px->conf.args.file,
	                                   px->conf.args.line, err, &px->conf.args, NULL);
	if (!rule->arg.expr)
		return ACT_RET_PRS_ERR;

	if (px->cap & PR_CAP_FE)
		where |= SMP_VAL_FE_HRQ_HDR;
	if (px->cap & PR_CAP_BE)
		where |= SMP_VAL_BE_HRQ_HDR;

	if (!(rule->arg.expr->fetch->val & where)) {
		memprintf(err,
			  "fetch method '%s' extracts information from '%s', none of which is available here",
			  args[0], sample_src_names(rule->arg.expr->fetch->use));
		free(rule->arg.expr);
		return ACT_RET_PRS_ERR;
	}

	rule->action     = ACT_CUSTOM;
	rule->action_ptr = action_set_priority_class;
	return ACT_RET_PRS_OK;
}

static enum act_parse_ret parse_set_priority_offset(const char **args, int *arg, struct proxy *px,
                                                    struct act_rule *rule, char **err)
{
	unsigned int where = 0;

	rule->arg.expr = sample_parse_expr((char **)args, arg, px->conf.args.file,
	                                   px->conf.args.line, err, &px->conf.args, NULL);
	if (!rule->arg.expr)
		return ACT_RET_PRS_ERR;

	if (px->cap & PR_CAP_FE)
		where |= SMP_VAL_FE_HRQ_HDR;
	if (px->cap & PR_CAP_BE)
		where |= SMP_VAL_BE_HRQ_HDR;

	if (!(rule->arg.expr->fetch->val & where)) {
		memprintf(err,
			  "fetch method '%s' extracts information from '%s', none of which is available here",
			  args[0], sample_src_names(rule->arg.expr->fetch->use));
		free(rule->arg.expr);
		return ACT_RET_PRS_ERR;
	}

	rule->action     = ACT_CUSTOM;
	rule->action_ptr = action_set_priority_offset;
	return ACT_RET_PRS_OK;
}

static struct action_kw_list tcp_cont_kws = {ILH, {
	{ "set-priority-class", parse_set_priority_class },
	{ "set-priority-offset", parse_set_priority_offset },
	{ /* END */ }
}};

INITCALL1(STG_REGISTER, tcp_req_cont_keywords_register, &tcp_cont_kws);

static struct action_kw_list http_req_kws = {ILH, {
	{ "set-priority-class", parse_set_priority_class },
	{ "set-priority-offset", parse_set_priority_offset },
	{ /* END */ }
}};

INITCALL1(STG_REGISTER, http_req_keywords_register, &http_req_kws);

static int
smp_fetch_priority_class(const struct arg *args, struct sample *smp, const char *kw, void *private)
{
	if (!smp->strm)
		return 0;

	smp->data.type = SMP_T_SINT;
	smp->data.u.sint = smp->strm->priority_class;

	return 1;
}

static int
smp_fetch_priority_offset(const struct arg *args, struct sample *smp, const char *kw, void *private)
{
	if (!smp->strm)
		return 0;

	smp->data.type = SMP_T_SINT;
	smp->data.u.sint = smp->strm->priority_offset;

	return 1;
}


static struct sample_fetch_kw_list smp_kws = {ILH, {
	{ "prio_class", smp_fetch_priority_class, 0, NULL, SMP_T_SINT, SMP_USE_INTRN, },
	{ "prio_offset", smp_fetch_priority_offset, 0, NULL, SMP_T_SINT, SMP_USE_INTRN, },
	{ /* END */},
}};

INITCALL1(STG_REGISTER, sample_register_fetches, &smp_kws);

/*
 * Local variables:
 *  c-indent-level: 8
 *  c-basic-offset: 8
 * End:
 */