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+/*++
+/* NAME
+/* qmgr_job 3
+/* SUMMARY
+/* per-transport jobs
+/* SYNOPSIS
+/* #include "qmgr.h"
+/*
+/* QMGR_JOB *qmgr_job_obtain(message, transport)
+/* QMGR_MESSAGE *message;
+/* QMGR_TRANSPORT *transport;
+/*
+/* void qmgr_job_free(job)
+/* QMGR_JOB *job;
+/*
+/* void qmgr_job_move_limits(job)
+/* QMGR_JOB *job;
+/*
+/* QMGR_ENTRY *qmgr_job_entry_select(transport)
+/* QMGR_TRANSPORT *transport;
+/*
+/* void qmgr_job_blocker_update(queue)
+/* QMGR_QUEUE *queue;
+/* DESCRIPTION
+/* These routines add/delete/manipulate per-transport jobs.
+/* Each job corresponds to a specific transport and message.
+/* Each job has a peer list containing all pending delivery
+/* requests for that message.
+/*
+/* qmgr_job_obtain() finds an existing job for named message and
+/* transport combination. New empty job is created if no existing can
+/* be found. In either case, the job is prepared for assignment of
+/* (more) message recipients.
+/*
+/* qmgr_job_free() disposes of a per-transport job after all
+/* its entries have been taken care of. It is an error to dispose
+/* of a job that is still in use.
+/*
+/* qmgr_job_entry_select() attempts to find the next entry suitable
+/* for delivery. The job preempting algorithm is also exercised.
+/* If necessary, an attempt to read more recipients into core is made.
+/* This can result in creation of more job, queue and entry structures.
+/*
+/* qmgr_job_blocker_update() updates the status of blocked
+/* jobs after a decrease in the queue's concurrency level,
+/* after the queue is throttled, or after the queue is resumed
+/* from suspension.
+/*
+/* qmgr_job_move_limits() takes care of proper distribution of the
+/* per-transport recipients limit among the per-transport jobs.
+/* Should be called whenever a job's recipient slot becomes available.
+/* DIAGNOSTICS
+/* Panic: consistency check failure.
+/* LICENSE
+/* .ad
+/* .fi
+/* The Secure Mailer license must be distributed with this software.
+/* AUTHOR(S)
+/* Patrik Rak
+/* patrik@raxoft.cz
+/*--*/
+
+/* System library. */
+
+#include <sys_defs.h>
+
+/* Utility library. */
+
+#include <msg.h>
+#include <htable.h>
+#include <mymalloc.h>
+#include <sane_time.h>
+
+/* Application-specific. */
+
+#include "qmgr.h"
+
+/* Forward declarations */
+
+static void qmgr_job_pop(QMGR_JOB *);
+
+/* Helper macros */
+
+#define HAS_ENTRIES(job) ((job)->selected_entries < (job)->read_entries)
+
+/*
+ * The MIN_ENTRIES macro may underestimate a lot but we can't use message->rcpt_unread
+ * because we don't know if all those unread recipients go to our transport yet.
+ */
+
+#define MIN_ENTRIES(job) ((job)->read_entries)
+#define MAX_ENTRIES(job) ((job)->read_entries + (job)->message->rcpt_unread)
+
+#define RESET_CANDIDATE_CACHE(transport) ((transport)->candidate_cache_current = 0)
+
+#define IS_BLOCKER(job,transport) ((job)->blocker_tag == (transport)->blocker_tag)
+
+/* qmgr_job_create - create and initialize message job structure */
+
+static QMGR_JOB *qmgr_job_create(QMGR_MESSAGE *message, QMGR_TRANSPORT *transport)
+{
+ QMGR_JOB *job;
+
+ job = (QMGR_JOB *) mymalloc(sizeof(QMGR_JOB));
+ job->message = message;
+ QMGR_LIST_APPEND(message->job_list, job, message_peers);
+ htable_enter(transport->job_byname, message->queue_id, (void *) job);
+ job->transport = transport;
+ QMGR_LIST_INIT(job->transport_peers);
+ QMGR_LIST_INIT(job->time_peers);
+ job->stack_parent = 0;
+ QMGR_LIST_INIT(job->stack_children);
+ QMGR_LIST_INIT(job->stack_siblings);
+ job->stack_level = -1;
+ job->blocker_tag = 0;
+ job->peer_byname = htable_create(0);
+ QMGR_LIST_INIT(job->peer_list);
+ job->slots_used = 0;
+ job->slots_available = 0;
+ job->selected_entries = 0;
+ job->read_entries = 0;
+ job->rcpt_count = 0;
+ job->rcpt_limit = 0;
+ return (job);
+}
+
+/* qmgr_job_link - append the job to the job lists based on the time it was queued */
+
+static void qmgr_job_link(QMGR_JOB *job)
+{
+ QMGR_TRANSPORT *transport = job->transport;
+ QMGR_MESSAGE *message = job->message;
+ QMGR_JOB *prev, *next, *list_prev, *list_next, *unread, *current;
+ int delay;
+
+ /*
+ * Sanity checks.
+ */
+ if (job->stack_level >= 0)
+ msg_panic("qmgr_job_link: already on the job lists (%d)", job->stack_level);
+
+ /*
+ * Traverse the time list and the scheduler list from the end and stop
+ * when we found job older than the one being linked.
+ *
+ * During the traversals keep track if we have come across either the
+ * current job or the first unread job on the job list. If this is the
+ * case, these pointers will be adjusted below as required.
+ *
+ * Although both lists are exactly the same when only jobs on the stack
+ * level zero are considered, it's easier to traverse them separately.
+ * Otherwise it's impossible to keep track of the current job pointer
+ * effectively.
+ *
+ * This may look inefficient but under normal operation it is expected that
+ * the loops will stop right away, resulting in normal list appends
+ * below. However, this code is necessary for reviving retired jobs and
+ * for jobs which are created long after the first chunk of recipients
+ * was read in-core (either of these can happen only for multi-transport
+ * messages).
+ *
+ * XXX Note that we test stack_parent rather than stack_level below. This
+ * subtle difference allows us to enqueue the job in correct time order
+ * with respect to orphaned children even after their original parent on
+ * level zero is gone. Consequently, the early loop stop in candidate
+ * selection works reliably, too. These are the reasons why we care to
+ * bother with children adoption at all.
+ */
+ current = transport->job_current;
+ for (next = 0, prev = transport->job_list.prev; prev;
+ next = prev, prev = prev->transport_peers.prev) {
+ if (prev->stack_parent == 0) {
+ delay = message->queued_time - prev->message->queued_time;
+ if (delay >= 0)
+ break;
+ }
+ if (current == prev)
+ current = 0;
+ }
+ list_prev = prev;
+ list_next = next;
+
+ unread = transport->job_next_unread;
+ for (next = 0, prev = transport->job_bytime.prev; prev;
+ next = prev, prev = prev->time_peers.prev) {
+ delay = message->queued_time - prev->message->queued_time;
+ if (delay >= 0)
+ break;
+ if (unread == prev)
+ unread = 0;
+ }
+
+ /*
+ * Link the job into the proper place on the job lists and mark it so we
+ * know it has been linked.
+ */
+ job->stack_level = 0;
+ QMGR_LIST_LINK(transport->job_list, list_prev, job, list_next, transport_peers);
+ QMGR_LIST_LINK(transport->job_bytime, prev, job, next, time_peers);
+
+ /*
+ * Update the current job pointer if necessary.
+ */
+ if (current == 0)
+ transport->job_current = job;
+
+ /*
+ * Update the pointer to the first unread job on the job list and steal
+ * the unused recipient slots from the old one.
+ */
+ if (unread == 0) {
+ unread = transport->job_next_unread;
+ transport->job_next_unread = job;
+ if (unread != 0)
+ qmgr_job_move_limits(unread);
+ }
+
+ /*
+ * Get as much recipient slots as possible. The excess will be returned
+ * to the transport pool as soon as the exact amount required is known
+ * (which is usually after all recipients have been read in core).
+ */
+ if (transport->rcpt_unused > 0) {
+ job->rcpt_limit += transport->rcpt_unused;
+ message->rcpt_limit += transport->rcpt_unused;
+ transport->rcpt_unused = 0;
+ }
+}
+
+/* qmgr_job_find - lookup job associated with named message and transport */
+
+static QMGR_JOB *qmgr_job_find(QMGR_MESSAGE *message, QMGR_TRANSPORT *transport)
+{
+
+ /*
+ * Instead of traversing the message job list, we use single per
+ * transport hash table. This is better (at least with respect to memory
+ * usage) than having single hash table (usually almost empty) for each
+ * message.
+ */
+ return ((QMGR_JOB *) htable_find(transport->job_byname, message->queue_id));
+}
+
+/* qmgr_job_obtain - find/create the appropriate job and make it ready for new recipients */
+
+QMGR_JOB *qmgr_job_obtain(QMGR_MESSAGE *message, QMGR_TRANSPORT *transport)
+{
+ QMGR_JOB *job;
+
+ /*
+ * Try finding an existing job, reviving it if it was already retired.
+ * Create a new job for this transport/message combination otherwise. In
+ * either case, the job ends linked on the job lists.
+ */
+ if ((job = qmgr_job_find(message, transport)) == 0)
+ job = qmgr_job_create(message, transport);
+ if (job->stack_level < 0)
+ qmgr_job_link(job);
+
+ /*
+ * Reset the candidate cache because of the new expected recipients. Make
+ * sure the job is not marked as a blocker for the same reason. Note that
+ * this can result in having a non-blocker followed by more blockers.
+ * Consequently, we can't just update the current job pointer, we have to
+ * reset it. Fortunately qmgr_job_entry_select() will easily deal with
+ * this and will lookup the real current job for us.
+ */
+ RESET_CANDIDATE_CACHE(transport);
+ if (IS_BLOCKER(job, transport)) {
+ job->blocker_tag = 0;
+ transport->job_current = transport->job_list.next;
+ }
+ return (job);
+}
+
+/* qmgr_job_move_limits - move unused recipient slots to the next unread job */
+
+void qmgr_job_move_limits(QMGR_JOB *job)
+{
+ QMGR_TRANSPORT *transport = job->transport;
+ QMGR_MESSAGE *message = job->message;
+ QMGR_JOB *next = transport->job_next_unread;
+ int rcpt_unused, msg_rcpt_unused;
+
+ /*
+ * Find next unread job on the job list if necessary. Cache it for later.
+ * This makes the amortized efficiency of this routine O(1) per job. Note
+ * that we use the time list whose ordering doesn't change over time.
+ */
+ if (job == next) {
+ for (next = next->time_peers.next; next; next = next->time_peers.next)
+ if (next->message->rcpt_offset != 0)
+ break;
+ transport->job_next_unread = next;
+ }
+
+ /*
+ * Calculate the number of available unused slots.
+ */
+ rcpt_unused = job->rcpt_limit - job->rcpt_count;
+ msg_rcpt_unused = message->rcpt_limit - message->rcpt_count;
+ if (msg_rcpt_unused < rcpt_unused)
+ rcpt_unused = msg_rcpt_unused;
+
+ /*
+ * Transfer the unused recipient slots back to the transport pool and to
+ * the next not-fully-read job. Job's message limits are adjusted
+ * accordingly. Note that the transport pool can be negative if we used
+ * some of the rcpt_per_stack slots.
+ */
+ if (rcpt_unused > 0) {
+ job->rcpt_limit -= rcpt_unused;
+ message->rcpt_limit -= rcpt_unused;
+ transport->rcpt_unused += rcpt_unused;
+ if (next != 0 && (rcpt_unused = transport->rcpt_unused) > 0) {
+ next->rcpt_limit += rcpt_unused;
+ next->message->rcpt_limit += rcpt_unused;
+ transport->rcpt_unused = 0;
+ }
+ }
+}
+
+/* qmgr_job_parent_gone - take care of orphaned stack children */
+
+static void qmgr_job_parent_gone(QMGR_JOB *job, QMGR_JOB *parent)
+{
+ QMGR_JOB *child;
+
+ while ((child = job->stack_children.next) != 0) {
+ QMGR_LIST_UNLINK(job->stack_children, QMGR_JOB *, child, stack_siblings);
+ if (parent != 0)
+ QMGR_LIST_APPEND(parent->stack_children, child, stack_siblings);
+ child->stack_parent = parent;
+ }
+}
+
+/* qmgr_job_unlink - unlink the job from the job lists */
+
+static void qmgr_job_unlink(QMGR_JOB *job)
+{
+ const char *myname = "qmgr_job_unlink";
+ QMGR_TRANSPORT *transport = job->transport;
+
+ /*
+ * Sanity checks.
+ */
+ if (job->stack_level != 0)
+ msg_panic("%s: non-zero stack level (%d)", myname, job->stack_level);
+ if (job->stack_parent != 0)
+ msg_panic("%s: parent present", myname);
+ if (job->stack_siblings.next != 0)
+ msg_panic("%s: siblings present", myname);
+
+ /*
+ * Make sure that children of job on zero stack level are informed that
+ * their parent is gone too.
+ */
+ qmgr_job_parent_gone(job, 0);
+
+ /*
+ * Update the current job pointer if necessary.
+ */
+ if (transport->job_current == job)
+ transport->job_current = job->transport_peers.next;
+
+ /*
+ * Invalidate the candidate selection cache if necessary.
+ */
+ if (job == transport->candidate_cache
+ || job == transport->candidate_cache_current)
+ RESET_CANDIDATE_CACHE(transport);
+
+ /*
+ * Remove the job from the job lists and mark it as unlinked.
+ */
+ QMGR_LIST_UNLINK(transport->job_list, QMGR_JOB *, job, transport_peers);
+ QMGR_LIST_UNLINK(transport->job_bytime, QMGR_JOB *, job, time_peers);
+ job->stack_level = -1;
+}
+
+/* qmgr_job_retire - remove the job from the job lists while waiting for recipients to deliver */
+
+static void qmgr_job_retire(QMGR_JOB *job)
+{
+ if (msg_verbose)
+ msg_info("qmgr_job_retire: %s", job->message->queue_id);
+
+ /*
+ * Pop the job from the job stack if necessary.
+ */
+ if (job->stack_level > 0)
+ qmgr_job_pop(job);
+
+ /*
+ * Make sure this job is not cached as the next unread job for this
+ * transport. The qmgr_entry_done() will make sure that the slots donated
+ * by this job are moved back to the transport pool as soon as possible.
+ */
+ qmgr_job_move_limits(job);
+
+ /*
+ * Remove the job from the job lists. Note that it remains on the message
+ * job list, though, and that it can be revived by using
+ * qmgr_job_obtain(). Also note that the available slot counter is left
+ * intact.
+ */
+ qmgr_job_unlink(job);
+}
+
+/* qmgr_job_free - release the job structure */
+
+void qmgr_job_free(QMGR_JOB *job)
+{
+ const char *myname = "qmgr_job_free";
+ QMGR_MESSAGE *message = job->message;
+ QMGR_TRANSPORT *transport = job->transport;
+
+ if (msg_verbose)
+ msg_info("%s: %s %s", myname, message->queue_id, transport->name);
+
+ /*
+ * Sanity checks.
+ */
+ if (job->rcpt_count)
+ msg_panic("%s: non-zero recipient count (%d)", myname, job->rcpt_count);
+
+ /*
+ * Pop the job from the job stack if necessary.
+ */
+ if (job->stack_level > 0)
+ qmgr_job_pop(job);
+
+ /*
+ * Return any remaining recipient slots back to the recipient slots pool.
+ */
+ qmgr_job_move_limits(job);
+ if (job->rcpt_limit)
+ msg_panic("%s: recipient slots leak (%d)", myname, job->rcpt_limit);
+
+ /*
+ * Unlink and discard the structure. Check if the job is still linked on
+ * the job lists or if it was already retired before unlinking it.
+ */
+ if (job->stack_level >= 0)
+ qmgr_job_unlink(job);
+ QMGR_LIST_UNLINK(message->job_list, QMGR_JOB *, job, message_peers);
+ htable_delete(transport->job_byname, message->queue_id, (void (*) (void *)) 0);
+ htable_free(job->peer_byname, (void (*) (void *)) 0);
+ myfree((void *) job);
+}
+
+/* qmgr_job_count_slots - maintain the delivery slot counters */
+
+static void qmgr_job_count_slots(QMGR_JOB *job)
+{
+
+ /*
+ * Count the number of delivery slots used during the delivery of the
+ * selected job. Also count the number of delivery slots available for
+ * its preemption.
+ *
+ * Despite its trivial look, this is one of the key parts of the theory
+ * behind this preempting scheduler.
+ */
+ job->slots_available++;
+ job->slots_used++;
+
+ /*
+ * If the selected job is not the original current job, reset the
+ * candidate cache because the change above have slightly increased the
+ * chance of this job becoming a candidate next time.
+ *
+ * Don't expect that the change of the current jobs this turn will render
+ * the candidate cache invalid the next turn - it can happen that the
+ * next turn the original current job will be selected again and the
+ * cache would be considered valid in such case.
+ */
+ if (job != job->transport->candidate_cache_current)
+ RESET_CANDIDATE_CACHE(job->transport);
+}
+
+/* qmgr_job_candidate - find best job candidate for preempting given job */
+
+static QMGR_JOB *qmgr_job_candidate(QMGR_JOB *current)
+{
+ QMGR_TRANSPORT *transport = current->transport;
+ QMGR_JOB *job, *best_job = 0;
+ double score, best_score = 0.0;
+ int max_slots, max_needed_entries, max_total_entries;
+ int delay;
+ time_t now = sane_time();
+
+ /*
+ * Fetch the result directly from the cache if the cache is still valid.
+ *
+ * Note that we cache negative results too, so the cache must be invalidated
+ * by resetting the cached current job pointer, not the candidate pointer
+ * itself.
+ *
+ * In case the cache is valid and contains no candidate, we can ignore the
+ * time change, as it affects only which candidate is the best, not if
+ * one exists. However, this feature requires that we no longer relax the
+ * cache resetting rules, depending on the automatic cache timeout.
+ */
+ if (transport->candidate_cache_current == current
+ && (transport->candidate_cache_time == now
+ || transport->candidate_cache == 0))
+ return (transport->candidate_cache);
+
+ /*
+ * Estimate the minimum amount of delivery slots that can ever be
+ * accumulated for the given job. All jobs that won't fit into these
+ * slots are excluded from the candidate selection.
+ */
+ max_slots = (MIN_ENTRIES(current) - current->selected_entries
+ + current->slots_available) / transport->slot_cost;
+
+ /*
+ * Select the candidate with best time_since_queued/total_recipients
+ * score. In addition to jobs which don't meet the max_slots limit, skip
+ * also jobs which don't have any selectable entries at the moment.
+ *
+ * Instead of traversing the whole job list we traverse it just from the
+ * current job forward. This has several advantages. First, we skip some
+ * of the blocker jobs and the current job itself right away. But the
+ * really important advantage is that we are sure that we don't consider
+ * any jobs that are already stack children of the current job. Thanks to
+ * this we can easily include all encountered jobs which are leaf
+ * children of some of the preempting stacks as valid candidates. All we
+ * need to do is to make sure we do not include any of the stack parents.
+ * And, because the leaf children are not ordered by the time since
+ * queued, we have to exclude them from the early loop end test.
+ *
+ * However, don't bother searching if we can't find anything suitable
+ * anyway.
+ */
+ if (max_slots > 0) {
+ for (job = current->transport_peers.next; job; job = job->transport_peers.next) {
+ if (job->stack_children.next != 0 || IS_BLOCKER(job, transport))
+ continue;
+ max_total_entries = MAX_ENTRIES(job);
+ max_needed_entries = max_total_entries - job->selected_entries;
+ delay = now - job->message->queued_time + 1;
+ if (max_needed_entries > 0 && max_needed_entries <= max_slots) {
+ score = (double) delay / max_total_entries;
+ if (score > best_score) {
+ best_score = score;
+ best_job = job;
+ }
+ }
+
+ /*
+ * Stop early if the best score is as good as it can get.
+ */
+ if (delay <= best_score && job->stack_level == 0)
+ break;
+ }
+ }
+
+ /*
+ * Cache the result for later use.
+ */
+ transport->candidate_cache = best_job;
+ transport->candidate_cache_current = current;
+ transport->candidate_cache_time = now;
+
+ return (best_job);
+}
+
+/* qmgr_job_preempt - preempt large message with smaller one */
+
+static QMGR_JOB *qmgr_job_preempt(QMGR_JOB *current)
+{
+ const char *myname = "qmgr_job_preempt";
+ QMGR_TRANSPORT *transport = current->transport;
+ QMGR_JOB *job, *prev;
+ int expected_slots;
+ int rcpt_slots;
+
+ /*
+ * Suppress preempting completely if the current job is not big enough to
+ * accumulate even the minimal number of slots required.
+ *
+ * Also, don't look for better job candidate if there are no available slots
+ * yet (the count can get negative due to the slot loans below).
+ */
+ if (current->slots_available <= 0
+ || MAX_ENTRIES(current) < transport->min_slots * transport->slot_cost)
+ return (current);
+
+ /*
+ * Find best candidate for preempting the current job.
+ *
+ * Note that the function also takes care that the candidate fits within the
+ * number of delivery slots which the current job is still able to
+ * accumulate.
+ */
+ if ((job = qmgr_job_candidate(current)) == 0)
+ return (current);
+
+ /*
+ * Sanity checks.
+ */
+ if (job == current)
+ msg_panic("%s: attempt to preempt itself", myname);
+ if (job->stack_children.next != 0)
+ msg_panic("%s: already on the job stack (%d)", myname, job->stack_level);
+ if (job->stack_level < 0)
+ msg_panic("%s: not on the job list (%d)", myname, job->stack_level);
+
+ /*
+ * Check if there is enough available delivery slots accumulated to
+ * preempt the current job.
+ *
+ * The slot loaning scheme improves the average message response time. Note
+ * that the loan only allows the preemption happen earlier, though. It
+ * doesn't affect how many slots have to be "paid" - in either case the
+ * full number of slots required has to be accumulated later before the
+ * current job can be preempted again.
+ */
+ expected_slots = MAX_ENTRIES(job) - job->selected_entries;
+ if (current->slots_available / transport->slot_cost + transport->slot_loan
+ < expected_slots * transport->slot_loan_factor / 100.0)
+ return (current);
+
+ /*
+ * Preempt the current job.
+ *
+ * This involves placing the selected candidate in front of the current job
+ * on the job list and updating the stack parent/child/sibling pointers
+ * appropriately. But first we need to make sure that the candidate is
+ * taken from its previous job stack which it might be top of.
+ */
+ if (job->stack_level > 0)
+ qmgr_job_pop(job);
+ QMGR_LIST_UNLINK(transport->job_list, QMGR_JOB *, job, transport_peers);
+ prev = current->transport_peers.prev;
+ QMGR_LIST_LINK(transport->job_list, prev, job, current, transport_peers);
+ job->stack_parent = current;
+ QMGR_LIST_APPEND(current->stack_children, job, stack_siblings);
+ job->stack_level = current->stack_level + 1;
+
+ /*
+ * Update the current job pointer and explicitly reset the candidate
+ * cache.
+ */
+ transport->job_current = job;
+ RESET_CANDIDATE_CACHE(transport);
+
+ /*
+ * Since the single job can be preempted by several jobs at the same
+ * time, we have to adjust the available slot count now to prevent using
+ * the same slots multiple times. To do that we subtract the number of
+ * slots the preempting job will supposedly use. This number will be
+ * corrected later when that job is popped from the stack to reflect the
+ * number of slots really used.
+ *
+ * As long as we don't need to keep track of how many slots were really
+ * used, we can (ab)use the slots_used counter for counting the
+ * difference between the real and expected amounts instead of the
+ * absolute amount.
+ */
+ current->slots_available -= expected_slots * transport->slot_cost;
+ job->slots_used = -expected_slots;
+
+ /*
+ * Add part of extra recipient slots reserved for preempting jobs to the
+ * new current job if necessary.
+ *
+ * Note that transport->rcpt_unused is within <-rcpt_per_stack,0> in such
+ * case.
+ */
+ if (job->message->rcpt_offset != 0) {
+ rcpt_slots = (transport->rcpt_per_stack + transport->rcpt_unused + 1) / 2;
+ job->rcpt_limit += rcpt_slots;
+ job->message->rcpt_limit += rcpt_slots;
+ transport->rcpt_unused -= rcpt_slots;
+ }
+ if (msg_verbose)
+ msg_info("%s: %s by %s, level %d", myname, current->message->queue_id,
+ job->message->queue_id, job->stack_level);
+
+ return (job);
+}
+
+/* qmgr_job_pop - remove the job from its job preemption stack */
+
+static void qmgr_job_pop(QMGR_JOB *job)
+{
+ const char *myname = "qmgr_job_pop";
+ QMGR_TRANSPORT *transport = job->transport;
+ QMGR_JOB *parent;
+
+ if (msg_verbose)
+ msg_info("%s: %s", myname, job->message->queue_id);
+
+ /*
+ * Sanity checks.
+ */
+ if (job->stack_level <= 0)
+ msg_panic("%s: not on the job stack (%d)", myname, job->stack_level);
+
+ /*
+ * Adjust the number of delivery slots available to preempt job's parent.
+ * Note that the -= actually adds back any unused slots, as we have
+ * already subtracted the expected amount of slots from both counters
+ * when we did the preemption.
+ *
+ * Note that we intentionally do not adjust slots_used of the parent. Doing
+ * so would decrease the maximum per message inflation factor if the
+ * preemption appeared near the end of parent delivery.
+ *
+ * For the same reason we do not adjust parent's slots_available if the
+ * parent is not the original parent that was preempted by this job
+ * (i.e., the original parent job has already completed).
+ *
+ * This is another key part of the theory behind this preempting scheduler.
+ */
+ if ((parent = job->stack_parent) != 0
+ && job->stack_level == parent->stack_level + 1)
+ parent->slots_available -= job->slots_used * transport->slot_cost;
+
+ /*
+ * Remove the job from its parent's children list.
+ */
+ if (parent != 0) {
+ QMGR_LIST_UNLINK(parent->stack_children, QMGR_JOB *, job, stack_siblings);
+ job->stack_parent = 0;
+ }
+
+ /*
+ * If there is a parent, let it adopt all those orphaned children.
+ * Otherwise at least notify the children that their parent is gone.
+ */
+ qmgr_job_parent_gone(job, parent);
+
+ /*
+ * Put the job back to stack level zero.
+ */
+ job->stack_level = 0;
+
+ /*
+ * Explicitly reset the candidate cache. It's not worth trying to skip
+ * this under some complicated conditions - in most cases the popped job
+ * is the current job so we would have to reset it anyway.
+ */
+ RESET_CANDIDATE_CACHE(transport);
+
+ /*
+ * Here we leave the remaining work involving the proper placement on the
+ * job list to the caller. The most important reason for this is that it
+ * allows us not to look up where exactly to place the job.
+ *
+ * The caller is also made responsible for invalidating the current job
+ * cache if necessary.
+ */
+#if 0
+ QMGR_LIST_UNLINK(transport->job_list, QMGR_JOB *, job, transport_peers);
+ QMGR_LIST_LINK(transport->job_list, some_prev, job, some_next, transport_peers);
+
+ if (transport->job_current == job)
+ transport->job_current = job->transport_peers.next;
+#endif
+}
+
+/* qmgr_job_peer_select - select next peer suitable for delivery */
+
+static QMGR_PEER *qmgr_job_peer_select(QMGR_JOB *job)
+{
+ QMGR_PEER *peer;
+ QMGR_MESSAGE *message = job->message;
+
+ /*
+ * Try reading in more recipients. We do that as soon as possible
+ * (almost, see below), to make sure there is enough new blood pouring
+ * in. Otherwise single recipient for slow destination might starve the
+ * entire message delivery, leaving lot of fast destination recipients
+ * sitting idle in the queue file.
+ *
+ * Ideally we would like to read in recipients whenever there is a space,
+ * but to prevent excessive I/O, we read them only when enough time has
+ * passed or we can read enough of them at once.
+ *
+ * Note that even if we read the recipients few at a time, the message
+ * loading code tries to put them to existing recipient entries whenever
+ * possible, so the per-destination recipient grouping is not grossly
+ * affected.
+ *
+ * XXX Workaround for logic mismatch. The message->refcount test needs
+ * explanation. If the refcount is zero, it means that qmgr_active_done()
+ * is being completed asynchronously. In such case, we can't read in
+ * more recipients as bad things would happen after qmgr_active_done()
+ * continues processing. Note that this results in the given job being
+ * stalled for some time, but fortunately this particular situation is so
+ * rare that it is not critical. Still we seek for better solution.
+ */
+ if (message->rcpt_offset != 0
+ && message->refcount > 0
+ && (message->rcpt_limit - message->rcpt_count >= job->transport->refill_limit
+ || (message->rcpt_limit > message->rcpt_count
+ && sane_time() - message->refill_time >= job->transport->refill_delay)))
+ qmgr_message_realloc(message);
+
+ /*
+ * Get the next suitable peer, if there is any.
+ */
+ if (HAS_ENTRIES(job) && (peer = qmgr_peer_select(job)) != 0)
+ return (peer);
+
+ /*
+ * There is no suitable peer in-core, so try reading in more recipients
+ * if possible. This is our last chance to get suitable peer before
+ * giving up on this job for now.
+ *
+ * XXX For message->refcount, see above.
+ */
+ if (message->rcpt_offset != 0
+ && message->refcount > 0
+ && message->rcpt_limit > message->rcpt_count) {
+ qmgr_message_realloc(message);
+ if (HAS_ENTRIES(job))
+ return (qmgr_peer_select(job));
+ }
+ return (0);
+}
+
+/* qmgr_job_entry_select - select next entry suitable for delivery */
+
+QMGR_ENTRY *qmgr_job_entry_select(QMGR_TRANSPORT *transport)
+{
+ QMGR_JOB *job, *next;
+ QMGR_PEER *peer;
+ QMGR_ENTRY *entry;
+
+ /*
+ * Get the current job if there is one.
+ */
+ if ((job = transport->job_current) == 0)
+ return (0);
+
+ /*
+ * Exercise the preempting algorithm if enabled.
+ *
+ * The slot_cost equal to 1 causes the algorithm to degenerate and is
+ * therefore disabled too.
+ */
+ if (transport->slot_cost >= 2)
+ job = qmgr_job_preempt(job);
+
+ /*
+ * Select next entry suitable for delivery. In case the current job can't
+ * provide one because of the per-destination concurrency limits, we mark
+ * it as a "blocker" job and continue with the next job on the job list.
+ *
+ * Note that the loop also takes care of getting the "stall" jobs (job with
+ * no entries currently available) out of the way if necessary. Stall
+ * jobs can appear in case of multi-transport messages whose recipients
+ * don't fit in-core at once. Some jobs created by such message may have
+ * only few recipients and would stay on the job list until all other
+ * jobs of that message are delivered, blocking precious recipient slots
+ * available to this transport. Or it can happen that the job has some
+ * more entries but suddenly they all get deferred. Whatever the reason,
+ * we retire such jobs below if we happen to come across some.
+ */
+ for ( /* empty */ ; job; job = next) {
+ next = job->transport_peers.next;
+
+ /*
+ * Don't bother if the job is known to have no available entries
+ * because of the per-destination concurrency limits.
+ */
+ if (IS_BLOCKER(job, transport))
+ continue;
+
+ if ((peer = qmgr_job_peer_select(job)) != 0) {
+
+ /*
+ * We have found a suitable peer. Select one of its entries and
+ * adjust the delivery slot counters.
+ */
+ entry = qmgr_entry_select(peer);
+ qmgr_job_count_slots(job);
+
+ /*
+ * Remember the current job for the next time so we don't have to
+ * crawl over all those blockers again. They will be reconsidered
+ * when the concurrency limit permits.
+ */
+ transport->job_current = job;
+
+ /*
+ * In case we selected the very last job entry, remove the job
+ * from the job lists right now.
+ *
+ * This action uses the assumption that once the job entry has been
+ * selected, it can be unselected only before the message ifself
+ * is deferred. Thus the job with all entries selected can't
+ * re-appear with more entries available for selection again
+ * (without reading in more entries from the queue file, which in
+ * turn invokes qmgr_job_obtain() which re-links the job back on
+ * the lists if necessary).
+ *
+ * Note that qmgr_job_move_limits() transfers the recipients slots
+ * correctly even if the job is unlinked from the job list thanks
+ * to the job_next_unread caching.
+ */
+ if (!HAS_ENTRIES(job) && job->message->rcpt_offset == 0)
+ qmgr_job_retire(job);
+
+ /*
+ * Finally. Hand back the fruit of our tedious effort.
+ */
+ return (entry);
+ } else if (HAS_ENTRIES(job)) {
+
+ /*
+ * The job can't be selected due the concurrency limits. Mark it
+ * together with its queues so we know they are blocking the job
+ * list and they get the appropriate treatment. In particular,
+ * all blockers will be reconsidered when one of the problematic
+ * queues will accept more deliveries. And the job itself will be
+ * reconsidered if it is assigned some more entries.
+ */
+ job->blocker_tag = transport->blocker_tag;
+ for (peer = job->peer_list.next; peer; peer = peer->peers.next)
+ if (peer->entry_list.next != 0)
+ peer->queue->blocker_tag = transport->blocker_tag;
+ } else {
+
+ /*
+ * The job is "stalled". Retire it until it either gets freed or
+ * gets more entries later.
+ */
+ qmgr_job_retire(job);
+ }
+ }
+
+ /*
+ * We have not found any entry we could use for delivery. Well, things
+ * must have changed since this transport was selected for asynchronous
+ * allocation. Never mind. Clear the current job pointer and reluctantly
+ * report back that we have failed in our task.
+ */
+ transport->job_current = 0;
+ return (0);
+}
+
+/* qmgr_job_blocker_update - update "blocked job" status */
+
+void qmgr_job_blocker_update(QMGR_QUEUE *queue)
+{
+ QMGR_TRANSPORT *transport = queue->transport;
+
+ /*
+ * If the queue was blocking some of the jobs on the job list, check if
+ * the concurrency limit has lifted. If there are still some pending
+ * deliveries, give it a try and unmark all transport blockers at once.
+ * The qmgr_job_entry_select() will do the rest. In either case make sure
+ * the queue is not marked as a blocker anymore, with extra handling of
+ * queues which were declared dead.
+ *
+ * Note that changing the blocker status also affects the candidate cache.
+ * Most of the cases would be automatically recognized by the current job
+ * change, but we play safe and reset the cache explicitly below.
+ *
+ * Keeping the transport blocker tag odd is an easy way to make sure the tag
+ * never matches jobs that are not explicitly marked as blockers.
+ */
+ if (queue->blocker_tag == transport->blocker_tag) {
+ if (queue->window > queue->busy_refcount && queue->todo.next != 0) {
+ transport->blocker_tag += 2;
+ transport->job_current = transport->job_list.next;
+ transport->candidate_cache_current = 0;
+ }
+ if (queue->window > queue->busy_refcount || QMGR_QUEUE_THROTTLED(queue))
+ queue->blocker_tag = 0;
+ }
+}