Cut CPU use and move heavy work off the UI thread

Redraws:
- Merge bursts of session and bandmap events into one redraw
  (Coalesced). Closed Bandmap and Available windows now unsubscribe.
- Grayline and Voice Keyer no longer subscribe to the session twice.
- Available summary, Score table and Log rows redraw only when their
  contents change. Telnet lines are added in batches.
- Bandmap view reuses its layout, shaped text and brushes. Grayline
  draws the coastlines as one cached shape.

Threads:
- Available, Bandmap colours, Check and Statistics do their judging
  and counting on the thread pool and draw the result on the UI thread.
- ContestLog takes a lock in Judge and in each method that changes the
  log, so a background Judge cannot read the indexes mid-edit.

Refresh rate:
- Statistics refreshes every 30 seconds and when the QSO count changes.
- Grayline refreshes at most every 15 seconds on session events.

Publish with ReadyToRun to cut startup JIT time.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

publish.sh

@@ -30,7 +30,7 @@ if [ -f "$archive" ]; then
 fi
 
 for project in Nonemm.App Nonemm.Recorder.App; do
-    ./build.sh publish "src/$project" -c Release -r "$rid" --self-contained -o "$out" || exit 1
+    ./build.sh publish "src/$project" -c Release -r "$rid" --self-contained -p:PublishReadyToRun=true -o "$out" || exit 1
 done
 rm -f "$out"/*.pdb
 

src/Nonemm.App/Windows/AvailableWindow.axaml.cs

@@ -44,6 +44,7 @@ public sealed partial class AvailableWindow : RefreshableWindow
     private AvailableRow? menuRow;
     private bool menuOnHeader;
     private string shownKey = "";
+    private string summaryKey = "";
     private DateTime pausedUntil = DateTime.MinValue;
     private bool refreshPending;
     private int ticks;
@@ -70,7 +71,10 @@ public sealed partial class AvailableWindow : RefreshableWindow
         Spots.PointerExited += (_, _) => Resume();
         Spots.LoadingRow += (_, e) => Paint(e.Row);
         Spots.ContextMenu = BuildMenu();
-        session.Bandmap.Changed += (_, _) => Dispatcher.UIThread.Post(Refresh);
+        Coalesced changed = new(Refresh);
+        EventHandler spotsChanged = (_, _) => changed.Request();
+        session.Bandmap.Changed += spotsChanged;
+        Closed += (_, _) => session.Bandmap.Changed -= spotsChanged;
         timer.Tick += (_, _) => OnTick();
         timer.Start();
         Closed += (_, _) => timer.Stop();
@@ -191,64 +195,137 @@ public sealed partial class AvailableWindow : RefreshableWindow
 
     // ---- refresh
 
+    private bool running;
+    private bool again;
+
+    /// Judging every spot and building the lines is done on other threads, so
+    /// a refresh never holds up a key press. A request that comes in while one
+    /// is running is answered by one more run afterwards, and the run it
+    /// replaces is not drawn.
     public override void Refresh()
     {
         refreshPending = false;
         ticks = 0;
-        Summary.Children.Clear();
-        Summary.RowDefinitions.Clear();
-        Summary.ColumnDefinitions.Clear();
+        if (running)
+        {
+            again = true;
+            return;
+        }
+        _ = RunAsync();
+    }
+
+    private async Task RunAsync()
+    {
+        running = true;
+        try
+        {
+            do
+            {
+                again = false;
+                await Update();
+            }
+            while (again);
+        }
+        finally
+        {
+            running = false;
+        }
+    }
+
+    /// What the other threads work out, so the UI thread only has to draw it.
+    private sealed record SummaryData(
+        IReadOnlyList<Band> Columns,
+        Dictionary<Band, int> Mults,
+        Dictionary<Band, int> Qs,
+        int MostMults,
+        int MostQs);
+
+    private sealed record Computed(int Mults, int Total, SummaryData? Summary, List<AvailableRow> Rows, string RowsKey);
+
+    private async Task Update()
+    {
         Summary.IsVisible = session.Settings.AvailableShowsSummary;
         bool multsOnly = session.Settings.AvailableMultsOnly;
         ModeButton.Content = multsOnly ? "Mults" : "Mults & Qs";
         ModeButton.Foreground = multsOnly ? Verdicts.NewMultiplier : Verdicts.Worth;
-        if (session.Available is null)
+        if (session.Available is not { } available)
         {
             StatusText.Text = "no contest is open";
             Spots.ItemsSource = Array.Empty<AvailableRow>();
             shownKey = "";
+            summaryKey = "";
+            Summary.Children.Clear();
             return;
         }
 
+        // everything the other threads read is taken here
         DateTime now = DateTime.UtcNow;
-        session.Bandmap.DropOlderThan(now);
-        IReadOnlyList<AvailableStation> all = session.Available.All();
-        if (Summary.IsVisible)
+        Settings settings = session.Settings;
+        BandPlan plan = session.BandPlan;
+        Bandmap bandmap = session.Bandmap;
+        HashSet<Band> picked = [.. clicked];
+        Frequency? tuned = session.Position?.Frequency;
+        bool summaryShown = Summary.IsVisible;
+        bandmap.DropOlderThan(now);
+        IReadOnlyList<AvailableStation> all = await available.AllAsync();
+        Computed computed = await Task.Run(() => Compute(all, now, settings, plan, bandmap, picked, tuned, summaryShown));
+        if (again)
         {
-            BuildSummary(all);
+            return;
         }
-        int mults = all.Count(s => s.IsMultiplier);
-        Title = $"Available Mults and Qs — {all.Count - mults} Qs · {mults} Mults · {all.Count} total";
-        StatusText.Text = all.Count == 0
+
+        if (computed.Summary is { } summary)
+        {
+            BuildSummary(summary, settings, picked);
+        }
+        Title = $"Available Mults and Qs — {computed.Total - computed.Mults} Qs · {computed.Mults} Mults · {computed.Total} total";
+        StatusText.Text = computed.Total == 0
             ? "No workable spots: check the contest, the bands and the cluster filters"
-            : $"{mults} mults · {all.Count - mults} Qs · {all.Count} total";
+            : $"{computed.Mults} mults · {computed.Total - computed.Mults} Qs · {computed.Total} total";
         if (IsPaused)
         {
             refreshPending = true;
             return;
         }
+        Show(computed.Rows, computed.RowsKey);
+    }
 
-        IReadOnlyList<string> preferred = session.Settings.SpotFilter.PreferredSpotters;
-        Frequency? tuned = session.Position?.Frequency;
+    private Computed Compute(
+        IReadOnlyList<AvailableStation> all,
+        DateTime now,
+        Settings settings,
+        BandPlan plan,
+        Bandmap bandmap,
+        HashSet<Band> picked,
+        Frequency? tuned,
+        bool summaryShown)
+    {
+        int mults = all.Count(s => s.IsMultiplier);
+        IReadOnlyList<string> preferred = settings.SpotFilter.PreferredSpotters;
         List<AvailableRow> rows = all
-            .Where(s => (!multsOnly || s.IsMultiplier) && IsShown(s))
+            .Where(s => (!settings.AvailableMultsOnly || s.IsMultiplier) && IsShown(s, settings, plan, picked))
             .Select(s => new AvailableRow(
                 s,
-                ModeName(s.Spot.Frequency),
+                ModeName(plan, s.Spot.Frequency),
                 now,
-                session.Bandmap.Remaining(s.Spot),
+                bandmap.Remaining(s.Spot),
                 preferred.Contains(s.Spot.Spotter, StringComparer.OrdinalIgnoreCase),
                 tuned is { } at && Math.Abs(at.Hertz - s.Spot.Frequency.Hertz) <= 100))
             .ToList();
-        Show(rows);
+        return new Computed(
+            mults,
+            all.Count,
+            summaryShown ? SummaryOf(all, settings) : null,
+            rows,
+            string.Join(';', rows.Select(r => r.Key)));
     }
 
-    private bool IsShown(AvailableStation station)
+    private static bool IsShown(AvailableStation station, Settings settings, BandPlan plan, HashSet<Band> picked)
     {
-        IReadOnlyList<string> bands = session.Settings.AvailableBands;
-        IReadOnlyList<string> modes = session.Settings.AvailableModes;
-        ModeCategory? category = session.BandPlan.ModeAt(station.Spot.Frequency);
-        return (clicked.Count == 0 || clicked.Contains(station.Band))
+        IReadOnlyList<string> bands = settings.AvailableBands;
+        IReadOnlyList<string> modes = settings.AvailableModes;
+        ModeCategory? category = plan.ModeAt(station.Spot.Frequency);
+        return (picked.Count == 0 || picked.Contains(station.Band))
             && (bands.Count == 0 || bands.Contains(station.Band.Name, StringComparer.OrdinalIgnoreCase))
             && (modes.Count == 0 || category is null || modes.Contains(ModeKey(category.Value), StringComparer.OrdinalIgnoreCase));
     }
@@ -262,9 +339,8 @@ public sealed partial class AvailableWindow : RefreshableWindow
 
     /// A refresh that changes nothing leaves the list alone, so the scroll
     /// position and the picked line stay where the operator left them.
-    private void Show(List<AvailableRow> rows)
+    private void Show(List<AvailableRow> rows, string key)
     {
-        string key = string.Join(';', rows.Select(r => r.Key));
         if (key == shownKey && Spots.ItemsSource is not null)
         {
             return;
@@ -280,13 +356,13 @@ public sealed partial class AvailableWindow : RefreshableWindow
         }
         string? picked = (Spots.SelectedItem as AvailableRow)?.Call;
         Spots.ItemsSource = view;
-        if (picked is not null && rows.FirstOrDefault(r => r.Call == picked) is { } again)
+        if (picked is not null && rows.FirstOrDefault(r => r.Call == picked) is { } same)
         {
-            Spots.SelectedItem = again;
+            Spots.SelectedItem = same;
         }
     }
 
-    private string ModeName(Frequency frequency) => session.BandPlan.ModeAt(frequency) switch
+    private static string ModeName(BandPlan plan, Frequency frequency) => plan.ModeAt(frequency) switch
     {
         ModeCategory.Cw => "CW",
         ModeCategory.Phone => "SSB",
@@ -309,22 +385,44 @@ public sealed partial class AvailableWindow : RefreshableWindow
 
     // ---- summary table
 
-    private IReadOnlyList<Band> SummaryBands(IReadOnlyList<AvailableStation> all)
+    private IReadOnlyList<Band> SummaryBands(IReadOnlyList<AvailableStation> all) =>
+        SummaryBands(all, session.Settings);
+
+    private static IReadOnlyList<Band> SummaryBands(IReadOnlyList<AvailableStation> all, Settings settings)
     {
-        IReadOnlyList<string> chosen = session.Settings.AvailableSummaryBands;
+        IReadOnlyList<string> chosen = settings.AvailableSummaryBands;
         IEnumerable<Band> basis = chosen.Count > 0
             ? chosen.Select(Bands.Named).OfType<Band>()
             : Bands.Contest;
         return [.. basis.Concat(all.Select(s => s.Band)).Distinct().OrderBy(b => b.Low.Hertz)];
     }
 
-    private void BuildSummary(IReadOnlyList<AvailableStation> all)
+    private static SummaryData SummaryOf(IReadOnlyList<AvailableStation> all, Settings settings)
     {
-        IReadOnlyList<Band> columns = SummaryBands(all);
+        IReadOnlyList<Band> columns = SummaryBands(all, settings);
         Dictionary<Band, int> mults = columns.ToDictionary(b => b, b => all.Count(s => s.Band == b && s.IsMultiplier));
         Dictionary<Band, int> qs = columns.ToDictionary(b => b, b => all.Count(s => s.Band == b && !s.IsMultiplier));
-        int mostMults = mults.Values.Max();
-        int mostQs = qs.Values.Max();
+        return new SummaryData(columns, mults, qs, mults.Values.Max(), qs.Values.Max());
+    }
+
+    private void BuildSummary(SummaryData data, Settings settings, HashSet<Band> picked)
+    {
+        (IReadOnlyList<Band> columns, Dictionary<Band, int> mults, Dictionary<Band, int> qs, int mostMults, int mostQs) = data;
+
+        // the table is built again only when a number, a highlight or the
+        // font size is different from what it shows
+        string key = string.Join(
+            ';',
+            columns.Select(b => $"{b.Name}:{mults[b]}:{qs[b]}:{picked.Contains(b)}"))
+            + $"|{mostMults}|{mostQs}|{settings.AvailableFontSize}";
+        if (key == summaryKey)
+        {
+            return;
+        }
+        summaryKey = key;
+        Summary.Children.Clear();
+        Summary.RowDefinitions.Clear();
+        Summary.ColumnDefinitions.Clear();
 
         for (int row = 0; row < 4; row++)
         {
@@ -344,7 +442,7 @@ public sealed partial class AvailableWindow : RefreshableWindow
         {
             Band band = columns[at];
             int column = at + 1;
-            Label(0, column, band.Name.TrimEnd('M', 'm'), e => ShowBands([band], null, e), clicked.Contains(band));
+            Label(0, column, band.Name.TrimEnd('M', 'm'), e => ShowBands([band], null, e), picked.Contains(band));
             Label(1, column, Count(mults[band]), e => ShowBands([band], true, e), mults[band] > 0 && mults[band] == mostMults);
             Label(2, column, Count(qs[band]), e => ShowBands([band], false, e), qs[band] > 0 && qs[band] == mostQs);
             Label(3, column, Count(mults[band] + qs[band]), e => ShowBands([band], null, e));

src/Nonemm.App/Windows/BandmapView.cs

@@ -99,14 +99,35 @@ public sealed class BandmapView : Control
         DrawSegments(context);
         DrawScale(context, ink);
         DrawVfos(context);
-        placed = [.. BandmapLayout.Place(Spots, scale, LabelHeight)
-            .Select(l => l with { MarkY = l.MarkY + Inset, LabelY = l.LabelY + Inset })];
+        PlaceLabels();
         foreach (BandmapLabel label in placed)
         {
             DrawLabel(context, label, ink);
         }
     }
 
+    private IReadOnlyList<Spot> placedSpots = [];
+    private BandmapScale? placedScale;
+    private double placedHeight;
+
+    /// Lays the callsigns out again only when the spots, the scale or the text
+    /// size are not what the last layout used. Redraws for any other reason, a
+    /// moving receiver bar for one, reuse it.
+    private void PlaceLabels()
+    {
+        if (placedScale == scale
+            && placedHeight == LabelHeight
+            && (ReferenceEquals(placedSpots, Spots) || placedSpots.SequenceEqual(Spots)))
+        {
+            return;
+        }
+        placedSpots = Spots;
+        placedScale = scale;
+        placedHeight = LabelHeight;
+        placed = [.. BandmapLayout.Place(Spots, scale, LabelHeight)
+            .Select(l => l with { MarkY = l.MarkY + Inset, LabelY = l.LabelY + Inset })];
+    }
+
     /// N1MM paints the CW, digital and phone parts of the band behind the
     /// scale, the digital block over the other two.
     /// Anything past a band edge is painted as out of band, which is the only
@@ -209,12 +230,20 @@ public sealed class BandmapView : Control
     protected override void OnPointerMoved(PointerEventArgs e)
     {
         base.OnPointerMoved(e);
+        Spot? under = LabelAt(e.GetPosition(this))?.Spot;
+        if (Equals(under, tipFor))
+        {
+            return;
+        }
+        tipFor = under;
         ToolTip.SetShowDelay(this, 0);
-        ToolTip.SetTip(
-            this,
-            LabelAt(e.GetPosition(this)) is { } label ? SpotDescription.Of(label.Spot) : null);
+        ToolTip.SetTip(this, under is null ? null : SpotDescription.Of(under));
     }
 
+    /// The spot the tool tip describes, so moving the pointer along a callsign
+    /// does not build the text again.
+    private Spot? tipFor;
+
     protected override void OnPointerPressed(PointerPressedEventArgs e)
     {
         base.OnPointerPressed(e);
@@ -227,23 +256,56 @@ public sealed class BandmapView : Control
         FrequencyPicked?.Invoke(this, scale.At(at.Y - Inset));
     }
 
-    private FormattedText Text(string text, IBrush brush, double size, bool bold = false, bool italic = false) =>
-        new(
+    /// Shaping text is the dearest part of a redraw, and the same few hundred
+    /// callsigns and frequency numbers are drawn every time, so each is kept.
+    private readonly Dictionary<(string Text, IBrush Brush, double Size, bool Bold, bool Italic), FormattedText> texts = [];
+
+    private FormattedText Text(string text, IBrush brush, double size, bool bold = false, bool italic = false)
+    {
+        if (texts.TryGetValue((text, brush, size, bold, italic), out FormattedText? kept))
+        {
+            return kept;
+        }
+        if (texts.Count > 2000)
+        {
+            texts.Clear();
+        }
+        FormattedText made = new(
             text,
             CultureInfo.InvariantCulture,
             FlowDirection.LeftToRight,
             bold ? boldTypeface : italic ? italicTypeface : typeface,
             size,
             brush);
+        texts[(text, brush, size, bold, italic)] = made;
+        return made;
+    }
 
     /// The form's text colour, which the theme sets in both light and dark.
     private IBrush Foreground() =>
         this.FindResource("FormForeground") as IBrush ?? Brushes.Gray;
 
-    private static IBrush Opaque(IBrush ink, double opacity) =>
-        ink is ISolidColorBrush solid
-            ? new SolidColorBrush(solid.Color, opacity)
-            : ink;
+    private readonly Dictionary<(IBrush Ink, double Opacity), IBrush> faded = [];
+
+    /// Kept, so the same brush comes back each time and the text drawn with it
+    /// is found in `texts`.
+    private IBrush Opaque(IBrush ink, double opacity)
+    {
+        if (ink is not ISolidColorBrush solid)
+        {
+            return ink;
+        }
+        if (!faded.TryGetValue((ink, opacity), out IBrush? brush))
+        {
+            if (faded.Count > 50)
+            {
+                faded.Clear();
+            }
+            brush = new SolidColorBrush(solid.Color, opacity);
+            faded[(ink, opacity)] = brush;
+        }
+        return brush;
+    }
 
     private static IBrush BrushFor(VfoRole role) => role switch
     {

src/Nonemm.App/Windows/BandmapWindow.axaml.cs

@@ -5,6 +5,7 @@ using Avalonia.Threading;
 using Nonemm.Contests;
 using Nonemm.Core;
 using Nonemm.Rig;
+using Nonemm.Session;
 using Nonemm.Spotting;
 
 namespace Nonemm.App.Windows;
@@ -76,7 +77,10 @@ public sealed partial class BandmapWindow : RefreshableWindow
             }
         };
         View.FrequencyPicked += (_, frequency) => tune(frequency, "");
-        session.Bandmap.Changed += (_, _) => Dispatcher.UIThread.Post(Refresh);
+        Coalesced changed = new(Refresh);
+        EventHandler spotsChanged = (_, _) => changed.Request();
+        session.Bandmap.Changed += spotsChanged;
+        Closed += (_, _) => session.Bandmap.Changed -= spotsChanged;
         EventHandler solarChanged = (_, _) => Dispatcher.UIThread.Post(ShowSolar);
         session.SolarChanged += solarChanged;
         Closed += (_, _) => session.SolarChanged -= solarChanged;
@@ -127,6 +131,56 @@ public sealed partial class BandmapWindow : RefreshableWindow
         View.Vfos = Vfos();
         View.Segments = session.BandPlan.For(band);
         View.InvalidateVisual();
+        _ = JudgeAsync();
+    }
+
+    /// What each callsign is worth, as of the last pass. The colours are looked
+    /// up when the view draws, so the log is never searched on the UI thread.
+    private Dictionary<Spot, Verdict?> verdicts = new(ReferenceEqualityComparer.Instance);
+    private bool judging;
+    private bool judgeAgain;
+
+    /// Judges every spot on another thread and draws again when that is done.
+    /// A request made while a pass is running is answered by one more pass.
+    private async Task JudgeAsync()
+    {
+        if (judging)
+        {
+            judgeAgain = true;
+            return;
+        }
+        judging = true;
+        try
+        {
+            do
+            {
+                judgeAgain = false;
+                OperatingPosition? position = session.Position;
+                Mode? mode = position?.Mode;
+                string contest = position?.Contest.Name ?? "";
+                IReadOnlyList<Spot> asked = View.Spots;
+                Dictionary<Spot, Verdict?> judged = await Task.Run(() =>
+                {
+                    Dictionary<Spot, Verdict?> found = new(ReferenceEqualityComparer.Instance);
+                    foreach (Spot spot in asked)
+                    {
+                        found[spot] = VerdictFor(position, mode, contest, spot);
+                    }
+                    return found;
+                });
+                if (judgeAgain)
+                {
+                    continue;
+                }
+                verdicts = judged;
+                View.InvalidateVisual();
+            }
+            while (judgeAgain);
+        }
+        finally
+        {
+            judging = false;
+        }
     }
 
     /// The bandmap's spots with the pseudospot for the CQ frequency, when the
@@ -206,11 +260,13 @@ public sealed partial class BandmapWindow : RefreshableWindow
     };
 
     private IBrush Colour(Spot spot) =>
-        spot.IsCqFrequency ? CqBrush : Verdicts.Colour(VerdictFor(spot));
+        spot.IsCqFrequency
+            ? CqBrush
+            : Verdicts.Colour(verdicts.GetValueOrDefault(spot));
 
-    private Verdict? VerdictFor(Spot spot)
+    private static Verdict? VerdictFor(OperatingPosition? position, Mode? mode, string contest, Spot spot)
     {
-        if (session.Position is null)
+        if (position is null || mode is null)
         {
             return null;
         }
@@ -219,14 +275,14 @@ public sealed partial class BandmapWindow : RefreshableWindow
             // N1MM marks a busy frequency as worked, so it is painted like one
             return Verdict.Dupe;
         }
-        return session.Position.Log.Judge(new Qso
+        return position.Log.Judge(new Qso
         {
             Id = "",
             TimestampUtc = DateTime.UtcNow,
             Call = spot.Call,
             Frequency = spot.Frequency,
-            Mode = session.Position.Mode,
-            ContestName = session.Position.Contest.Name,
+            Mode = mode,
+            ContestName = contest,
         });
     }
 }

src/Nonemm.App/Windows/CheckWindow.axaml.cs

@@ -29,14 +29,49 @@ public sealed partial class CheckWindow : RefreshableWindow
 
     public override void RefreshForEntry() => Refresh();
 
+    private bool running;
+    private bool again;
+
+    /// The search runs on another thread, so a key press never waits for it.
+    /// A request that comes in while one is running is answered by one more
+    /// run afterwards, which sees the latest call.
     public override void Refresh()
     {
-        Columns.Children.Clear();
-        if (session.Check is null)
+        if (running)
         {
+            again = true;
             return;
         }
-        IReadOnlyList<CheckColumn> columns = session.Check.Columns();
+        _ = RunAsync();
+    }
+
+    private async Task RunAsync()
+    {
+        running = true;
+        try
+        {
+            do
+            {
+                again = false;
+                await ShowColumns();
+            }
+            while (again);
+        }
+        finally
+        {
+            running = false;
+        }
+    }
+
+    private async Task ShowColumns()
+    {
+        if (session.Check is null)
+        {
+            Columns.Children.Clear();
+            return;
+        }
+        IReadOnlyList<CheckColumn> columns = await session.Check.ColumnsAsync();
+        Columns.Children.Clear();
         Columns.ColumnDefinitions.Clear();
         foreach (CheckColumn _ in columns)
         {

src/Nonemm.App/Windows/Coalesced.cs

@@ -0,0 +1,28 @@
+using Avalonia.Threading;
+
+namespace Nonemm.App.Windows;
+
+/// Runs an action on the UI thread once for any number of requests made before
+/// it runs. A radio turning its dial or a busy cluster raises an event many
+/// times a second, and each window only needs to redraw once the burst has been
+/// handled.
+public sealed class Coalesced(Action action)
+{
+    private int pending;
+
+    /// Safe to call from any thread.
+    public void Request()
+    {
+        if (Interlocked.Exchange(ref pending, 1) == 1)
+        {
+            return;
+        }
+        Dispatcher.UIThread.Post(
+            () =>
+            {
+                Volatile.Write(ref pending, 0);
+                action();
+            },
+            DispatcherPriority.Background);
+    }
+}

src/Nonemm.App/Windows/EntryWindow.axaml.cs

@@ -67,7 +67,9 @@ public sealed partial class EntryWindow : Window
         this.radioNumber = radioNumber;
         InitializeComponent();
         BuildFunctionKeys();
-        session.Changed += (_, _) => Dispatcher.UIThread.Post(Refresh);
+        // a radio being tuned raises this many times a second
+        Coalesced changed = new(Refresh);
+        session.Changed += (_, _) => changed.Request();
         // a keyer speaks on its own thread, and a recording that would not
         // play has nowhere else to be said
         session.Reported += (_, what) => Dispatcher.UIThread.Post(() => Status(what));
@@ -949,7 +951,7 @@ public sealed partial class EntryWindow : Window
         RefreshSelf();
         foreach (Window window in openWindows.Values)
         {
-            (window as RefreshableWindow)?.Refresh();
+            (window as RefreshableWindow)?.RefreshFromSession();
         }
     }
 

src/Nonemm.App/Windows/GraylineView.cs

@@ -49,24 +49,55 @@ public sealed class GraylineView : Control
         }
     }
 
+    private static readonly Pen CoastPen = new(Land, 1);
+    private Geometry? coastlines;
+    private Size coastlinesFor;
+
+    /// The coastlines are thousands of short segments, so they are built into
+    /// one shape that is kept until the window changes size.
     private void DrawCoastlines(DrawingContext context)
     {
-        Pen pen = new(Land, 1);
+        if (coastlines is null || coastlinesFor != Bounds.Size)
+        {
+            coastlines = BuildCoastlines();
+            coastlinesFor = Bounds.Size;
+        }
+        context.DrawGeometry(null, CoastPen, coastlines);
+    }
+
+    private StreamGeometry BuildCoastlines()
+    {
+        StreamGeometry shape = new();
+        using StreamGeometryContext path = shape.Open();
         foreach (IReadOnlyList<Point> line in WorldMap.Coastlines)
         {
-            for (int at = 1; at < line.Count; at++)
+            bool open = false;
+            for (int at = 0; at < line.Count; at++)
             {
-                Point from = line[at - 1];
                 Point to = line[at];
                 // a line that runs off one edge and back on at the other is the
                 // date line being crossed, and is left undrawn
-                if (Math.Abs(to.X - from.X) > 180)
+                if (open && Math.Abs(to.X - line[at - 1].X) > 180)
                 {
-                    continue;
+                    path.EndFigure(false);
+                    open = false;
                 }
-                context.DrawLine(pen, At(from.Y, from.X), At(to.Y, to.X));
+                if (open)
+                {
+                    path.LineTo(At(to.Y, to.X));
+                }
+                else
+                {
+                    path.BeginFigure(At(to.Y, to.X), isFilled: false);
+                    open = true;
+                }
+            }
+            if (open)
+            {
+                path.EndFigure(false);
             }
         }
+        return shape;
     }
 
     /// The night is one shape, its edge the terminator: the latitude where the

src/Nonemm.App/Windows/GraylineWindow.axaml.cs

@@ -25,23 +25,40 @@ public sealed partial class GraylineWindow : RefreshableWindow
         clock = new DispatcherTimer { Interval = TimeSpan.FromMinutes(1) };
         clock.Tick += (_, _) => Refresh();
         clock.Start();
-        session.Changed += WhenSessionChanged;
         Closed += (_, _) =>
         {
             clock.Stop();
-            session.Changed -= WhenSessionChanged;
+            later?.Cancel();
         };
         Refresh();
     }
 
     private OperatingPosition? Radio => session.Position;
 
-    public override void RefreshForEntry() => Refresh();
+    private Throttled? later;
+
+    /// The map is not watched closely: a station typed or spotted shows up
+    /// within fifteen seconds, and the grey line moves too slowly to see.
+    public override void RefreshForEntry() => RefreshFromSession();
+
+    public override void RefreshFromSession()
+    {
+        later ??= new Throttled(TimeSpan.FromSeconds(15), Refresh);
+        later.Request();
+    }
 
     public override void Refresh()
     {
-        Map.Moment = DateTime.UtcNow;
-        Map.Markers = Markers();
+        DateTime now = DateTime.UtcNow;
+        IReadOnlyList<MapMarker> markers = Markers();
+        // the terminator moves a quarter of a degree a minute, so a redraw
+        // for nothing but the clock can wait
+        if (now - Map.Moment < TimeSpan.FromSeconds(30) && Map.Markers.SequenceEqual(markers))
+        {
+            return;
+        }
+        Map.Moment = now;
+        Map.Markers = markers;
         Map.InvalidateVisual();
     }
 
@@ -95,8 +112,5 @@ public sealed partial class GraylineWindow : RefreshableWindow
     private CountryLookup? Where(string call) =>
         call.Trim().Length == 0 ? null : session.Countries?.Find(call.Trim());
 
-    private void WhenSessionChanged(object? sender, EventArgs e) =>
-        Dispatcher.UIThread.Post(Refresh);
-
     private sealed record Station(string Call, double Latitude, double Longitude, IBrush Colour);
 }

src/Nonemm.App/Windows/LogWindow.axaml.cs

@@ -223,7 +223,12 @@ public sealed partial class LogWindow : RefreshableWindow
             bool atBottom = ScrolledToBottom();
             for (int at = 0; at < shownRows.Count; at++)
             {
-                shownRows[at].Show(qsos[at], VerdictFor(qsos[at]));
+                // a contact that was not edited is the same object, and the
+                // row has nothing to redraw
+                if (!ReferenceEquals(shownRows[at].Qso, qsos[at]))
+                {
+                    shownRows[at].Show(qsos[at], VerdictFor(qsos[at]));
+                }
             }
             bool grown = qsos.Count > shownRows.Count;
             for (int at = shownRows.Count; at < qsos.Count; at++)

src/Nonemm.App/Windows/RefreshableWindow.cs

@@ -7,6 +7,11 @@ public abstract class RefreshableWindow : Window
 {
     public abstract void Refresh();
 
+    /// Called instead of `Refresh` when the session changes. A window that
+    /// does not need to follow every change redraws later here, while `Refresh`
+    /// stays immediate for what the operator does in the window itself.
+    public virtual void RefreshFromSession() => Refresh();
+
     /// Called instead of `Refresh` when the entry window's call or exchange
     /// changes. A window that shows nothing about them does nothing.
     public virtual void RefreshForEntry()

src/Nonemm.App/Windows/ScoreWindow.axaml.cs

@@ -19,13 +19,18 @@ public sealed partial class ScoreWindow : RefreshableWindow
     }
 
 
+    /// What the table and the total line showed last, so a refresh that
+    /// changes nothing leaves the controls alone.
+    private string shown = "";
+
     public override void Refresh()
     {
-        Table.Children.Clear();
-        Table.ColumnDefinitions.Clear();
-        Table.RowDefinitions.Clear();
         if (session.Logging is null)
         {
+            shown = "";
+            Table.Children.Clear();
+            Table.ColumnDefinitions.Clear();
+            Table.RowDefinitions.Clear();
             TotalText.Text = "no contest is open";
             return;
         }
@@ -39,32 +44,28 @@ public sealed partial class ScoreWindow : RefreshableWindow
             .ToList();
         bool hasKinds = session.Logging.Contest.HasQtcTraffic;
 
-        columnCount = hasKinds ? 5 : 4;
-        for (int column = 0; column < columnCount; column++)
-        {
-            Table.ColumnDefinitions.Add(new ColumnDefinition(GridLength.Star));
-        }
-        AddRow(0, "Band", "Q/QTC", "QSOs", "Points", "Mults", header: true);
-
-        int row = 1;
+        List<(string[] Cells, bool Header)> rows = [(["Band", "Q/QTC", "QSOs", "Points", "Mults"], true)];
         foreach ((ScoreKey key, ScoreTally line) in lines)
         {
-            AddRow(
-                row++,
-                key.Band,
-                key.Kind,
-                line.Qsos.ToString(),
-                line.Points.ToString(),
-                line.TotalMultipliers.ToString());
+            rows.Add((
+                [
+                    key.Band,
+                    key.Kind,
+                    line.Qsos.ToString(),
+                    line.Points.ToString(),
+                    line.TotalMultipliers.ToString(),
+                ],
+                false));
         }
-        AddRow(
-            row,
-            "Total",
-            hasKinds ? "All" : "",
-            session.Logging.Log.Tally.Qsos.ToString(),
-            session.Logging.Log.Tally.Points.ToString(),
-            session.Logging.Log.Tally.TotalMultipliers.ToString(),
-            header: true);
+        rows.Add((
+            [
+                "Total",
+                hasKinds ? "All" : "",
+                session.Logging.Log.Tally.Qsos.ToString(),
+                session.Logging.Log.Tally.Points.ToString(),
+                session.Logging.Log.Tally.TotalMultipliers.ToString(),
+            ],
+            true));
 
         TimeSpan on = OperatingTime.On(
             session.Logging.Log.Qsos,
@@ -72,10 +73,31 @@ public sealed partial class ScoreWindow : RefreshableWindow
         TimeSpan off = OperatingTime.Off(
             session.Logging.Log.Qsos,
             session.Logging.Contest.MinimumOffTime);
-        TotalText.Text =
+        string total =
             $"Claimed score {session.Logging.Log.TotalScore:N0}"
             + $"   on {Hours(on)}   off {Hours(off)}"
             + BandChanges();
+
+        string signature = hasKinds + "\n" + string.Join('\n', rows.Select(r => string.Join('\t', r.Cells)));
+        TotalText.Text = total;
+        if (signature == shown)
+        {
+            return;
+        }
+        shown = signature;
+
+        Table.Children.Clear();
+        Table.ColumnDefinitions.Clear();
+        Table.RowDefinitions.Clear();
+        columnCount = hasKinds ? 5 : 4;
+        for (int column = 0; column < columnCount; column++)
+        {
+            Table.ColumnDefinitions.Add(new ColumnDefinition(GridLength.Star));
+        }
+        for (int row = 0; row < rows.Count; row++)
+        {
+            AddRow(row, rows[row].Cells, rows[row].Header);
+        }
     }
 
     /// The band changes made and the allowance, for a contest that limits
@@ -92,19 +114,12 @@ public sealed partial class ScoreWindow : RefreshableWindow
     private static string Hours(TimeSpan time) =>
         $"{(int)time.TotalHours}:{time.Minutes:00}";
 
-    private void AddRow(
-        int row,
-        string band,
-        string kind,
-        string qsos,
-        string points,
-        string mults,
-        bool header = false)
+    private void AddRow(int row, string[] all, bool header)
     {
         Table.RowDefinitions.Add(new RowDefinition(GridLength.Auto));
         string[] cells = columnCount == 5
-            ? [band, kind, qsos, points, mults]
-            : [band, qsos, points, mults];
+            ? all
+            : [all[0], all[2], all[3], all[4]];
         for (int column = 0; column < cells.Length; column++)
         {
             TextBlock text = new()

src/Nonemm.App/Windows/StatisticsWindow.axaml.cs

@@ -8,7 +8,9 @@ using Avalonia.Interactivity;
 using Avalonia.Media;
 using Avalonia.Media.Imaging;
 using Avalonia.Platform.Storage;
+using Avalonia.Threading;
 using Nonemm.App.Configuration;
+using Nonemm.Core;
 using Nonemm.Session;
 
 namespace Nonemm.App.Windows;
@@ -55,55 +57,118 @@ public sealed partial class StatisticsWindow : RefreshableWindow
         loading = false;
 
         ShowPaletteBox();
+        DispatcherTimer every = new() { Interval = TimeSpan.FromSeconds(30) };
+        every.Tick += (_, _) => Refresh();
+        every.Start();
+        Closed += (_, _) => every.Stop();
         Refresh();
     }
 
+    /// How many contacts the figures were counted from.
+    private int countShown = -1;
+
+    /// The numbers are not watched as they change. They are counted again
+    /// every thirty seconds and when a contact has been logged or deleted; the
+    /// refresh button and the field boxes are immediate.
+    public override void RefreshFromSession()
+    {
+        if (session.Logging is { } logging && logging.Log.Qsos.Count != countShown)
+        {
+            Refresh();
+        }
+    }
+
     private StatisticsField Row =>
         StatisticsFields.Find(StatisticsFields.Rows, session.Settings.StatsRow);
 
     private StatisticsField Column =>
         StatisticsFields.Find(StatisticsFields.Columns, session.Settings.StatsColumn);
 
+    private bool running;
+    private bool again;
+
+    /// Counting the log is done on another thread, so a refresh never holds up
+    /// the entry window. A request made while one is running is answered by one
+    /// more run afterwards, and the run it replaces is not drawn.
     public override void Refresh()
     {
-        if (session.Logging is null)
+        if (running)
         {
-            Table.Columns.Clear();
-            Table.ItemsSource = Array.Empty<StatisticsRow>();
-            Chart.Columns = [];
-            Chart.Series = [];
-            Chart.InvalidateVisual();
-            laid = null;
-            Empty("no contest is open");
+            again = true;
+            return;
+        }
+        _ = RunAsync();
+    }
+
+    private async Task RunAsync()
+    {
+        running = true;
+        try
+        {
+            do
+            {
+                again = false;
+                await Update();
+            }
+            while (again);
+        }
+        finally
+        {
+            running = false;
+        }
+    }
+
+    private async Task Update()
+    {
+        if (session.Logging is not { } logging)
+        {
+            countShown = -1;
+            ShowNothing("no contest is open");
             return;
         }
 
-        StatisticsPivot pivot = StatisticsPivot.Of(
-            session.Logging.Log.Qsos,
-            Row,
-            Column,
-            session.Logging.Instance.StartDate,
-            session.Settings.StatsIncludeDupes);
-        Title = $"Statistics for {session.Logging.Contest.Name}"
-            + $" - {session.Logging.Instance.StartDate:yyyy-MM-dd}"
-            + $" - {Column.Name} by {Row.Name}";
-        if (pivot.IsEmpty)
+        // the log is changed on this thread, so the counting works on a copy
+        IReadOnlyList<Qso> qsos = [.. logging.Log.Qsos];
+        countShown = qsos.Count;
+        StatisticsField row = Row;
+        StatisticsField column = Column;
+        DateTime start = logging.Instance.StartDate;
+        bool dupes = session.Settings.StatsIncludeDupes;
+        (StatisticsPivot pivot, StatisticsTable? table) = await Task.Run(() =>
         {
-            Table.Columns.Clear();
-            Table.ItemsSource = Array.Empty<StatisticsRow>();
-            Chart.Columns = [];
-            Chart.Series = [];
-            Chart.InvalidateVisual();
-            laid = null;
-            Empty("no contacts are counted");
+            StatisticsPivot counted = StatisticsPivot.Of(qsos, row, column, start, dupes);
+            return (counted, counted.IsEmpty ? null : StatisticsTable.Of(counted));
+        });
+        if (again)
+        {
+            return;
+        }
+
+        Title = $"Statistics for {logging.Contest.Name}"
+            + $" - {start:yyyy-MM-dd}"
+            + $" - {column.Name} by {row.Name}";
+        if (table is null)
+        {
+            ShowNothing("no contacts are counted");
             return;
         }
         EmptyText.IsVisible = false;
         Table.IsVisible = true;
-        FillTable(pivot);
+        FillTable(table);
         FillChart(pivot);
     }
 
+    private void ShowNothing(string why)
+    {
+        Table.Columns.Clear();
+        Table.ItemsSource = Array.Empty<StatisticsRow>();
+        Chart.Columns = [];
+        Chart.Series = [];
+        Chart.InvalidateVisual();
+        laid = null;
+        Empty(why);
+    }
+
     private void Empty(string why)
     {
         EmptyText.Text = why;
@@ -111,9 +176,9 @@ public sealed partial class StatisticsWindow : RefreshableWindow
         Table.IsVisible = false;
     }
 
-    private void FillTable(StatisticsPivot pivot)
+    private void FillTable(StatisticsTable table)
     {
-        laid = StatisticsTable.Of(pivot);
+        laid = table;
         Table.Columns.Clear();
         for (int at = 0; at < laid.Headings.Count; at++)
         {

src/Nonemm.App/Windows/TelnetWindow.axaml.cs

@@ -143,26 +143,45 @@ public sealed partial class TelnetWindow : RefreshableWindow
     private void OnConnectionChanged(object? sender, bool connected) =>
         Dispatcher.UIThread.Post(Refresh);
 
-    /// `strong` marks the lines from a preferred spotter. The view stays on the
+    /// `strong` marks the lines from a preferred spotter. Lines wait here and go
+    /// into the list together, because a busy node sends dozens a second and
+    /// each one added alone lays the list out again. The view stays on the
     /// newest line; a burst of lines is scrolled once, after the last of them.
     private void Show(string line, IBrush? colour, bool strong = false) => Dispatcher.UIThread.Post(() =>
     {
-        while (Traffic.Items.Count >= LinesKept)
+        waiting.Add((line, colour, strong));
+        flushWaiting ??= new Coalesced(AddWaiting);
+        flushWaiting.Request();
+    });
+
+    private readonly List<(string Line, IBrush? Colour, bool Strong)> waiting = [];
+    private Coalesced? flushWaiting;
+
+    private void AddWaiting()
+    {
+        // lines that would be pushed out again at once are not added
+        int skip = Math.Max(0, waiting.Count - LinesKept);
+        int excess = Math.Max(0, Traffic.Items.Count + waiting.Count - skip - LinesKept);
+        for (int removed = 0; removed < excess && Traffic.Items.Count > 0; removed++)
         {
             Traffic.Items.RemoveAt(0);
         }
-        Traffic.Items.Add(new TextBlock
+        foreach ((string line, IBrush? colour, bool strong) in waiting.Skip(skip))
         {
-            Text = line,
-            Foreground = colour,
-            FontWeight = strong ? FontWeight.Bold : FontWeight.Normal,
-        });
+            Traffic.Items.Add(new TextBlock
+            {
+                Text = line,
+                Foreground = colour,
+                FontWeight = strong ? FontWeight.Bold : FontWeight.Normal,
+            });
+        }
+        waiting.Clear();
         if (!scrollPending)
         {
             scrollPending = true;
             Dispatcher.UIThread.Post(ScrollToNewest, DispatcherPriority.Background);
         }
-    });
+    }
 
     private void ScrollToNewest()
     {

src/Nonemm.App/Windows/Throttled.cs

@@ -0,0 +1,32 @@
+using Avalonia.Threading;
+
+namespace Nonemm.App.Windows;
+
+/// Runs an action once, `delay` after the first request, however many requests
+/// come in meanwhile. It is for windows that do not have to follow every
+/// change: the picture is at most `delay` old. Call it on the UI thread.
+public sealed class Throttled
+{
+    private readonly DispatcherTimer timer;
+
+    public Throttled(TimeSpan delay, Action action)
+    {
+        timer = new DispatcherTimer { Interval = delay };
+        timer.Tick += (_, _) =>
+        {
+            timer.Stop();
+            action();
+        };
+    }
+
+    public void Request()
+    {
+        if (!timer.IsEnabled)
+        {
+            timer.Start();
+        }
+    }
+
+    /// Drops a request that is waiting, for a window that has closed.
+    public void Cancel() => timer.Stop();
+}

src/Nonemm.App/Windows/VoiceKeyerWindow.axaml.cs

@@ -32,7 +32,6 @@ public sealed partial class VoiceKeyerWindow : RefreshableWindow
         RecordBox.LostFocus += (_, _) => SaveCommands();
         PttBox.IsCheckedChanged += (_, _) => SaveCommands();
         OperatorBox.SelectionChanged += (_, _) => Refresh();
-        session.Changed += (_, _) => Dispatcher.UIThread.Post(Refresh);
         FillOperators();
         Refresh();
     }

src/Nonemm.Contests/ContestLog.cs

@@ -22,6 +22,12 @@ public sealed class ContestLog
     private readonly Dictionary<ScoreKey, ScoreTally> rows = [];
     private ScoreTally tally = new();
 
+    /// `Judge` is called from a background thread by the windows that judge
+    /// every spot, while the UI thread adds and edits contacts. Both take this
+    /// lock around the indexes. The lock can be entered again by the thread
+    /// that holds it, because a rebuild judges each contact.
+    private readonly Lock guard = new();
+
     public ContestLog(
         Contest contest,
         StationInfo me,
@@ -67,6 +73,14 @@ public sealed class ContestLog
 
     /// What logging this contact right now would do, without logging it.
     public Verdict Judge(Qso candidate)
+    {
+        lock (guard)
+        {
+            return JudgeLocked(candidate);
+        }
+    }
+
+    private Verdict JudgeLocked(Qso candidate)
     {
         if (!candidate.IsClaimed)
         {
@@ -103,19 +117,25 @@ public sealed class ContestLog
     /// Adds the contact and returns it with points and multiplier flags filled in.
     public Qso Add(Qso qso)
     {
-        Verdict verdict = Judge(qso);
-        Qso scored = ApplyVerdict(qso, verdict);
-        qsos.Add(scored);
-        Index(scored, verdict);
-        return scored;
+        lock (guard)
+        {
+            Verdict verdict = Judge(qso);
+            Qso scored = ApplyVerdict(qso, verdict);
+            qsos.Add(scored);
+            Index(scored, verdict);
+            return scored;
+        }
     }
 
     /// Loads contacts read back from storage. Points and multiplier flags in
     /// the stored rows are ignored and worked out again from the rules.
     public void Restore(IEnumerable<Qso> stored)
     {
-        qsos.AddRange(stored);
-        Rebuild();
+        lock (guard)
+        {
+            qsos.AddRange(stored);
+            Rebuild();
+        }
     }
 
     /// Adds a contact that may be older than ones already logged, which is what
@@ -123,41 +143,56 @@ public sealed class ContestLog
     /// again: the earlier of two contacts is the one that claims a multiplier.
     public void Insert(Qso qso)
     {
-        qsos.Add(qso);
-        Rebuild();
+        lock (guard)
+        {
+            qsos.Add(qso);
+            Rebuild();
+        }
     }
 
     /// `Insert` for several contacts, scoring the log once instead of once per
     /// contact. A resync sends a few hundred in a burst.
     public void InsertRange(IEnumerable<Qso> arrived)
     {
-        qsos.AddRange(arrived);
-        Rebuild();
+        lock (guard)
+        {
+            qsos.AddRange(arrived);
+            Rebuild();
+        }
     }
 
     public void Remove(string id)
     {
-        qsos.RemoveAll(q => q.Id == id);
-        Rebuild();
+        lock (guard)
+        {
+            qsos.RemoveAll(q => q.Id == id);
+            Rebuild();
+        }
     }
 
     /// `Remove` for several contacts, scoring the log once.
     public void RemoveRange(IReadOnlyCollection<string> ids)
     {
         HashSet<string> gone = [.. ids];
-        qsos.RemoveAll(q => gone.Contains(q.Id));
-        Rebuild();
+        lock (guard)
+        {
+            qsos.RemoveAll(q => gone.Contains(q.Id));
+            Rebuild();
+        }
     }
 
     public void Replace(Qso qso)
     {
-        int at = qsos.FindIndex(q => q.Id == qso.Id);
-        if (at < 0)
+        lock (guard)
         {
-            throw new InvalidOperationException($"no contact with id {qso.Id} in the log");
+            int at = qsos.FindIndex(q => q.Id == qso.Id);
+            if (at < 0)
+            {
+                throw new InvalidOperationException($"no contact with id {qso.Id} in the log");
+            }
+            qsos[at] = qso;
+            Rebuild();
         }
-        qsos[at] = qso;
-        Rebuild();
     }
 
     /// A station worked before, under the contest's dupe rule. A contest with
@@ -284,7 +319,13 @@ public sealed class ContestLog
     /// rescores what it touches — but the stored points and multiplier flags
     /// are written from this, and a caller that is about to write them asks for
     /// a pass first.
-    public void Rescore() => Rebuild();
+    public void Rescore()
+    {
+        lock (guard)
+        {
+            Rebuild();
+        }
+    }
 
     /// Rescores the whole log. A removed or edited contact can hand its
     /// multiplier to a later one, which only a full pass gets right.

src/Nonemm.Session/AvailableStations.cs

@@ -47,16 +47,32 @@ public sealed class AvailableStations
 
     /// Every spotted station that is not a dupe, multipliers first and then in
     /// frequency order.
-    public IReadOnlyList<AvailableStation> All()
+    public IReadOnlyList<AvailableStation> All() =>
+        Build(bandmap.All(), position.Mode, position.Contest, position.Me);
+
+    /// `All` on a thread-pool thread, for the window that would otherwise
+    /// judge every spot between two key presses. What the position holds is
+    /// read here, on the caller's thread, and the log locks itself while it
+    /// judges.
+    public Task<IReadOnlyList<AvailableStation>> AllAsync()
+    {
+        IReadOnlyList<Spot> spots = bandmap.All();
+        Mode mode = position.Mode;
+        Contest contest = position.Contest;
+        StationInfo me = position.Me;
+        return Task.Run(() => Build(spots, mode, contest, me));
+    }
+
+    private IReadOnlyList<AvailableStation> Build(IReadOnlyList<Spot> spots, Mode mode, Contest contest, StationInfo me)
     {
         List<AvailableStation> found = [];
-        foreach (Spot spot in bandmap.All())
+        foreach (Spot spot in spots)
         {
             if (spot.Band is not { } band || !spot.IsStation)
             {
                 continue;
             }
-            Verdict verdict = position.Log.Judge(Candidate(spot));
+            Verdict verdict = position.Log.Judge(Candidate(spot, mode, contest, me));
             if (!verdict.IsDupe)
             {
                 found.Add(new AvailableStation(
@@ -73,7 +89,7 @@ public sealed class AvailableStations
             .ToList();
     }
 
-    private Qso Candidate(Spot spot)
+    private Qso Candidate(Spot spot, Mode mode, Contest contest, StationInfo me)
     {
         Qso qso = new()
         {
@@ -81,13 +97,13 @@ public sealed class AvailableStations
             TimestampUtc = DateTime.UtcNow,
             Call = spot.Call,
             Frequency = spot.Frequency,
-            Mode = position.Mode,
-            ContestName = position.Contest.Name,
+            Mode = mode,
+            ContestName = contest.Name,
         };
         return ExchangeSlots.ApplyHistory(
             CountryFields.Apply(qso, position.Session.Countries),
             position.Session.History,
-            position.Contest,
-            position.Me);
+            contest,
+            me);
     }
 }

src/Nonemm.Session/CheckWindowSources.cs

@@ -46,6 +46,44 @@ public sealed class CheckWindowSources
         ];
     }
 
+    /// `Columns`, with the searching done on another thread. The master
+    /// database holds tens of thousands of calls, and searching it between two
+    /// key presses is what makes typing stutter. The log, the history and the
+    /// bandmap are read here on the caller's thread, because the log is
+    /// changed there; the caller's thread also judges the few calls that are
+    /// shown, because that reads the log too.
+    public async Task<IReadOnlyList<CheckColumn>> ColumnsAsync(int limit = 24)
+    {
+        string query = (Elsewhere ?? session.Entry.Call).Trim().ToUpperInvariant();
+        IReadOnlyList<string> logged = LoggedCalls();
+        IReadOnlyList<string> history = HistoryCalls();
+        IReadOnlyList<string> spotted = SpottedCalls();
+        CheckColumn exchange = ExchangeColumn(limit);
+        bool searching = query.Length >= PartialMatching.ShortestUsefulQuery;
+        List<PartialMatch> none = [];
+        (List<PartialMatch> Log, List<PartialMatch> Master, List<PartialMatch> History, List<PartialMatch> Bandmap) found =
+            await Task.Run(() =>
+            {
+                if (!searching)
+                {
+                    return (none, none, none, none);
+                }
+                return (
+                    Best(logged, query, limit),
+                    database.Matches(query, limit).Select(m => m).ToList(),
+                    Best(history, query, limit),
+                    Best(spotted, query, limit));
+            });
+        return
+        [
+            new CheckColumn(CheckSource.Log, logged.Count, [.. found.Log.Select(Judged)]),
+            new CheckColumn(CheckSource.Database, database.Count, [.. found.Master.Select(Judged)]),
+            new CheckColumn(CheckSource.History, history.Count, [.. found.History.Select(Judged)]),
+            new CheckColumn(CheckSource.Bandmap, spotted.Count, [.. found.Bandmap.Select(Judged)]),
+            exchange,
+        ];
+    }
+
     /// What the exchange box with the cursor in it could hold: the ARRL
     /// sections, or the states and provinces. A serial number or a report has
     /// no list behind it, so the column stays empty.
@@ -81,19 +119,26 @@ public sealed class CheckWindowSources
         {
             return new CheckColumn(source, calls.Count, []);
         }
-        List<CheckCandidate> found = [];
+        return new CheckColumn(source, calls.Count, [.. Best(calls, query, limit).Select(Judged)]);
+    }
+
+    /// The calls that match the query, the closest first. It reads nothing but
+    /// its arguments, so it can run on any thread.
+    private static List<PartialMatch> Best(IReadOnlyList<string> calls, string query, int limit)
+    {
+        List<PartialMatch> found = [];
         foreach (string call in calls)
         {
             PartialMatchQuality? quality = PartialMatching.Judge(query, call);
             if (quality is not null)
             {
-                found.Add(Judged(new PartialMatch(call, quality.Value)));
+                found.Add(new PartialMatch(call, quality.Value));
             }
         }
-        return new CheckColumn(
-            source,
-            calls.Count,
-            found.OrderBy(c => c.Quality).ThenBy(c => c.Text, StringComparer.Ordinal).Take(limit).ToList());
+        return [.. found
+            .OrderBy(m => m.Quality)
+            .ThenBy(m => m.Call, StringComparer.Ordinal)
+            .Take(limit)];
     }
 
     private CheckCandidate Judged(PartialMatch match) =>