Fix iOS broadcast pump mapping churn

The screen-audio pump opened and disposed a memory mapping plus its container
lookup and path strings on every 5 ms tick - about 200 mapping pairs per
second of steady allocation that churned the GC under long calls. The producer
opens the ring with O_CREAT and never replaces it, so the pump now keeps one
mapping across ticks and rebuilds it only when the ring file disappears or a
drain fails.

clients/apple/VoiceCat.iOS/BroadcastAudioPump.cs

@@ -9,12 +9,15 @@ internal sealed class BroadcastAudioPump : IAsyncDisposable
     private const uint Magic = 0x56434252, Version = 1;
     private const int Header = 64, Capacity = 96_000, Frame = 960;
     private readonly CancellationTokenSource stop = new();
+    private readonly short[] scratch = new short[Frame * 2];
     private Thread? worker;
     private VoiceCatClient? client;
+    private MemoryMappedFile? map;
+    private MemoryMappedViewAccessor? view;
+    private string? path;
     private uint streamId;
     private bool active;
     private int generation;
-    private readonly short[] scratch = new short[Frame * 2];
 
     internal event Action? Changed;
     internal bool IsActive => active;
@@ -29,51 +32,92 @@ internal sealed class BroadcastAudioPump : IAsyncDisposable
     private void Run()
     {
         CancellationToken token = stop.Token;
-        while (!token.IsCancellationRequested)
+        try
         {
-            try { DrainAsync(token).GetAwaiter().GetResult(); }
-            catch (Exception exception) when (exception is IOException or UnauthorizedAccessException or InvalidDataException or OperationCanceledException) { }
-            if (!token.IsCancellationRequested) Thread.Sleep(5);
+            while (!token.IsCancellationRequested)
+            {
+                try { DrainAsync(token).GetAwaiter().GetResult(); }
+                catch (Exception exception) when (exception is IOException or UnauthorizedAccessException or InvalidDataException or OperationCanceledException) { CloseMapping(); }
+                if (!token.IsCancellationRequested) Thread.Sleep(5);
+            }
         }
+        finally { CloseMapping(); }
     }
 
     private async Task DrainAsync(CancellationToken token)
     {
-        NSUrl? root = NSFileManager.DefaultManager.GetContainerUrl(IosConstants.AppGroup);
-        if (root?.Path is null) return;
-        string path = Path.Combine(root.Path, "voicecat", "broadcast_audio.ring"); if (!File.Exists(path)) return;
-        using MemoryMappedFile map = MemoryMappedFile.CreateFromFile(path, FileMode.Open, null, Header + Capacity * sizeof(short), MemoryMappedFileAccess.ReadWrite);
-        using MemoryMappedViewAccessor view = map.CreateViewAccessor(0, Header + Capacity * sizeof(short), MemoryMappedFileAccess.ReadWrite);
-        if (view.ReadUInt32(0) != Magic || view.ReadUInt32(4) != Version) throw new InvalidDataException("Unsupported broadcast ring.");
-        bool active = view.ReadUInt32(16) != 0;
+        if (!OpenMapping()) return;
+        MemoryMappedViewAccessor pages = view!;
+        bool active = pages.ReadUInt32(16) != 0;
         if (!active) { StopStream(); SetActive(false); return; }
         VoiceCatClient owner = client ?? throw new IOException("Client disconnected.");
         if (streamId == 0)
         {
             int startGeneration = Volatile.Read(ref generation);
             StreamInfo stream = await owner.StartStreamAsync(StreamKind.StreamScreenAudio, "Screen audio", 2, token).ConfigureAwait(false);
-            if (startGeneration != Volatile.Read(ref generation) || view.ReadUInt32(16) == 0 || !ReferenceEquals(client, owner))
+            if (startGeneration != Volatile.Read(ref generation) || pages.ReadUInt32(16) == 0 || !ReferenceEquals(client, owner))
             {
                 try { owner.StopStream(stream.StreamId); } catch (Exception exception) when (exception is IOException or InvalidOperationException) { }
                 return;
             }
-            streamId = stream.StreamId; view.Write(32, view.ReadUInt64(24)); SetActive(true);
+            streamId = stream.StreamId; pages.Write(32, pages.ReadUInt64(24)); SetActive(true);
         }
-        ulong write = view.ReadUInt64(24), read = view.ReadUInt64(32);
+        ulong write = pages.ReadUInt64(24), read = pages.ReadUInt64(32);
         if (write - read > Capacity) read = write - Capacity;
         while (write - read >= Frame * 2)
         {
             for (int sample = 0; sample < scratch.Length; sample++)
             {
                 ulong index = (read + (ulong)sample) % Capacity;
-                scratch[sample] = view.ReadInt16(Header + checked((long)index * sizeof(short)));
+                scratch[sample] = pages.ReadInt16(Header + checked((long)index * sizeof(short)));
             }
             if (!owner.Audio.FeedPcm(streamId, scratch, 2)) break;
             read += (ulong)scratch.Length;
-            view.Write(32, read);
+            pages.Write(32, read);
         }
     }
 
+    // The producer opens the ring with O_CREAT and never replaces it, so one mapping covers the
+    // pump's whole life. Creating and disposing a mapping (plus its container lookup and path
+    // strings) every 5 ms tick allocated steadily at 200 Hz and churned the GC under long calls;
+    // the mapping is now built on the ring's transitions and reused until the file disappears or
+    // a drain fails.
+    private bool OpenMapping()
+    {
+        path ??= ResolvePath();
+        if (path is null) return false;
+        bool present = File.Exists(path);
+        if (view is not null)
+        {
+            if (present) return true;
+            CloseMapping(); return false;
+        }
+        if (!present) return false;
+        MemoryMappedFile candidate = MemoryMappedFile.CreateFromFile(path, FileMode.Open, null, Header + Capacity * sizeof(short), MemoryMappedFileAccess.ReadWrite);
+        try
+        {
+            MemoryMappedViewAccessor pages = candidate.CreateViewAccessor(0, Header + Capacity * sizeof(short), MemoryMappedFileAccess.ReadWrite);
+            if (pages.ReadUInt32(0) != Magic || pages.ReadUInt32(4) != Version)
+            {
+                pages.Dispose(); throw new InvalidDataException("Unsupported broadcast ring.");
+            }
+            map = candidate; view = pages; return true;
+        }
+        catch { candidate.Dispose(); throw; }
+    }
+
+    private static string? ResolvePath()
+    {
+        NSUrl? root = NSFileManager.DefaultManager.GetContainerUrl(IosConstants.AppGroup);
+        return root?.Path is null ? null : Path.Combine(root.Path, "voicecat", "broadcast_audio.ring");
+    }
+
+    private void CloseMapping()
+    {
+        view?.Dispose(); view = null;
+        map?.Dispose(); map = null;
+    }
+
     private void StopStream()
     {
         uint id = streamId; streamId = 0; if (id == 0 || client?.State != ClientConnectionState.Connected) return;

tests/VoiceCat.Tests/PublishServerScriptTests.cs

@@ -1,4 +1,5 @@
 using System.Diagnostics;
+using System.Text.RegularExpressions;
 
 namespace VoiceCat.Tests;
 
@@ -117,6 +118,25 @@ public class PublishServerScriptTests
         Assert.DoesNotContain("if (OperatingSystem.IsIOSVersionAtLeast(27)) { model.ToggleScreenAudio();", settings);
     }
 
+    [Fact]
+    public async Task IosBroadcastPumpKeepsOneRingMappingAcrossTicks()
+    {
+        string root = FindRoot();
+        string pump = await File.ReadAllTextAsync(Path.Combine(
+            root, "clients", "apple", "VoiceCat.iOS", "BroadcastAudioPump.cs"));
+
+        // A mapping pair plus its container lookup and path strings per 5 ms tick allocated
+        // steadily at 200 Hz and churned the GC under long calls. The pump opens one mapping on
+        // the ring's transitions and reuses it; the producer never replaces the ring file.
+        Assert.Single(Regex.Matches(pump, "MemoryMappedFile.CreateFromFile"));
+        Assert.Contains("private bool OpenMapping()", pump);
+        Assert.Contains("private void CloseMapping()", pump);
+        Assert.Contains("Thread.Sleep(5)", pump);
+        Assert.Contains("File.Exists(path)", pump);
+        Assert.DoesNotContain("using MemoryMappedFile", pump);
+        Assert.DoesNotContain("using MemoryMappedViewAccessor", pump);
+    }
+
     [Fact]
     public async Task IosCaptureDoesNotDependOnCoalescedManagedTimers()
     {