/*++ /* 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; /* 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_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, (char *) 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). */ 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 (*) (char *)) 0); htable_free(job->peer_byname, (void (*) (char *)) 0); myfree((char *) 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 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); }