Make a queue move lossless and run its passes on the acting controller alone (hq issue 558)

Review of #276: a move deleted before it published, so a failed publish
lost an ask; a verb's own process ran a pass beside the serving one, so
one could resume the queue while the other moved asks and a build ran
twice. The copy is now published first and second copies removed by id,
asks only signal the acting controller's loop, moves stop with 5 s of
the pause left, a cancel finds a moved ask by id, and an unreadable ask
keeps its age.

cmd/mesh-controller/queue.go

@@ -14,7 +14,6 @@ import (
 	"time"
 
 	"github.com/nats-io/nats.go"
-	"github.com/nats-io/nats.go/jetstream"
 
 	"github.com/novox/mesh-controller/internal/broker"
 	"github.com/novox/mesh-controller/internal/inventory"
@@ -81,37 +80,28 @@ func listQueue(ctx context.Context, args []string, w io.Writer) error {
 	return nil
 }
 
-// keepingTheQueueInOrder puts the build queue in order every watchEvery while this controller acts
-// (novox/hq issue 558). An ask puts it in order as it joins; this is for the clock: a check comes of age
-// with nothing asked.
+// keepingTheQueueInOrder runs the build queue's passes while this controller acts (novox/hq issue 558):
+// the one process that puts the queue in order, so no two passes pause and resume it over each other.
+// The build seat is read from the catalogue at most every half minute.
 func keepingTheQueueInOrder(ctx context.Context, open *stores, js *broker.JetStream) {
-	tick := time.NewTicker(watchEvery)
-	defer tick.Stop()
-	for {
-		select {
-		case <-ctx.Done():
-			return
-		case <-tick.C:
-		}
-		if !link.Holding() || js == nil {
-			continue
-		}
-		entries, err := open.inventory.Catalogued(ctx)
-		if err != nil {
-			fmt.Printf("the build queue is not put in order: the catalogue cannot be read: %v\n", err)
-			continue
-		}
-		seat := buildSeatAmong(entries)
-		ordering, cancel := context.WithTimeout(ctx, watchEvery)
-		moved, err := link.PutInOrder(ordering, js, seat)
-		cancel()
-		if len(moved) > 0 {
-			fmt.Printf("the %s queue put in order: %s moved behind what goes first\n", seat, strings.Join(moved, ", "))
-		}
-		if err != nil {
-			fmt.Printf("the %s queue could not be put in order: %v\n", seat, err)
-		}
+	if js == nil {
+		return
 	}
+	seat, readAt := link.TheBuildMachine, time.Time{}
+	seatNow := func() string {
+		if time.Since(readAt) < watchEvery {
+			return seat
+		}
+		if entries, err := open.inventory.Catalogued(ctx); err == nil {
+			seat, readAt = buildSeatAmong(entries), time.Now()
+		} else {
+			fmt.Printf("the build seat is read as %s: the catalogue cannot be read: %v\n", seat, err)
+		}
+		return seat
+	}
+	link.KeepingInOrder(ctx, js, seatNow, link.Holding, func(format string, args ...any) {
+		fmt.Printf(format+"\n", args...)
+	})
 }
 
 // queueAnswer is the queue as data (novox/hq issue 455): what a caller reads to say how far back an ask
@@ -307,6 +297,15 @@ func cancelAsk(ctx context.Context, js *broker.JetStream, open *stores, seat str
 		}
 	}
 	worker, _ := broker.HolderConsumerFor("", "", broker.DeclaredSeat{Name: seat, Accepts: []string{"build"}})
+	// **Where it waits now** (novox/hq issue 558): moved into order since it was read, a waiting ask has a
+	// later sequence, and the worker handing out what was behind its old one is not it being taken.
+	if ask.State == link.AskWaiting {
+		if q, err := link.ReadQueue(ctx, js, seat); err == nil {
+			if now, ok := q.Find(ask.ID); ok && now.State == link.AskWaiting {
+				ask.Seq = now.Seq
+			}
+		}
+	}
 	switch ask.State {
 	case link.AskWaiting:
 		if taken, err := takenSince(js, worker, ask.Seq); err != nil {
@@ -328,14 +327,25 @@ func cancelAsk(ctx context.Context, js *broker.JetStream, open *stores, seat str
 				"ends it there", ask.ID, started, ask.ID)
 		}
 	}
-	if err := js.Context().DeleteMsg(worker.Stream, ask.Seq); err != nil && !errors.Is(err, nats.ErrMsgNotFound) &&
-		!errors.Is(err, jetstream.ErrMsgNotFound) && !strings.Contains(err.Error(), "no message found") {
+	// Found by its id when it was moved into order since it was read (novox/hq issue 558).
+	removed, err := link.DeleteAsk(ctx, js, seat, ask)
+	if err != nil {
 		return "", fmt.Errorf("%s is marked cancelled and could not be deleted from the queue (seq %d): %w — a "+
 			"holder taking it ends it as cancelled", ask.ID, ask.Seq, err)
 	}
 	recordCancelled(ctx, open, ask)
-	return fmt.Sprintf("cancelled %s (%s, %s): deleted from the %s queue and recorded failed, %s — a plan "+
-		"that asked for it fails with that", ask.ID, ask.Repository, ask.State, seat, link.CancelledByHand), nil
+	return cancelSaid(ask, seat, removed), nil
+}
+
+// cancelSaid is what a cancel says: deleted from the queue only when it was.
+func cancelSaid(ask link.QueuedAsk, seat string, removed uint64) string {
+	where := fmt.Sprintf("deleted from the %s queue", seat)
+	if removed == 0 {
+		where = fmt.Sprintf("no longer in the %s queue to delete, and marked cancelled, so a holder taking it "+
+			"ends it", seat)
+	}
+	return fmt.Sprintf("cancelled %s (%s, %s): %s and recorded failed, %s — a plan "+
+		"that asked for it fails with that", ask.ID, ask.Repository, ask.State, where, link.CancelledByHand)
 }
 
 // holderLooks is how long a cancel waits for a holder that took the ask before the mark to say it

cmd/mesh-controller/queue_answer_test.go

@@ -142,3 +142,16 @@ func TestTheQueueNeverShowsARepositorysPassword(t *testing.T) {
 		}
 	}
 }
+
+// A cancel says it deleted the ask only when it did: moved into order and gone since, it says so (novox/hq
+// issue 558).
+func TestACancelSaysDeletedOnlyWhenItDeleted(t *testing.T) {
+	ask := link.QueuedAsk{ID: "build-1", Repository: "novox/x", State: link.AskWaiting, Seq: 4}
+	if said := cancelSaid(ask, link.TheBuildMachine, 9); !strings.Contains(said, "deleted from the") {
+		t.Errorf("removed, it says: %s", said)
+	}
+	if said := cancelSaid(ask, link.TheBuildMachine, 0); strings.Contains(said, "deleted from") ||
+		!strings.Contains(said, "no longer in the") {
+		t.Errorf("gone already, it says: %s", said)
+	}
+}