Track the number of live multiplexers, and report it in the error dump if non-trivial

Author: mgravell

src/StackExchange.Redis/ConnectionMultiplexer.Debug.cs

@@ -4,14 +4,24 @@ namespace StackExchange.Redis;
 
 public partial class ConnectionMultiplexer
 {
-    private static int _collectedWithoutDispose;
+    private static int _collectedWithoutDispose, s_MuxerDestroyCount, s_MuxerCreateCount;
     internal static int CollectedWithoutDispose => Volatile.Read(ref _collectedWithoutDispose);
 
+    internal static int GetLiveObjectCount(out int created, out int destroyed, out int nonDisposed)
+    {
+        // read destroy first, to prevent negative numbers in race conditions
+        destroyed = Volatile.Read(ref s_MuxerDestroyCount);
+        created = Volatile.Read(ref s_MuxerCreateCount);
+        nonDisposed = Volatile.Read(ref _collectedWithoutDispose);
+        return created - destroyed;
+    }
+
     /// <summary>
     /// Invoked by the garbage collector.
     /// </summary>
     ~ConnectionMultiplexer()
     {
+        Interlocked.Increment(ref s_MuxerDestroyCount);
         Interlocked.Increment(ref _collectedWithoutDispose);
     }
 

src/StackExchange.Redis/ConnectionMultiplexer.cs

@@ -128,6 +128,8 @@ static ConnectionMultiplexer()
 
         private ConnectionMultiplexer(ConfigurationOptions configuration, ServerType? serverType = null, EndPointCollection? endpoints = null)
         {
+            Interlocked.Increment(ref s_MuxerCreateCount);
+
             RawConfig = configuration ?? throw new ArgumentNullException(nameof(configuration));
             EndPoints = endpoints ?? RawConfig.EndPoints.Clone();
             EndPoints.SetDefaultPorts(serverType, ssl: RawConfig.Ssl);
@@ -2258,6 +2260,7 @@ ConfigurationChangedChannel is byte[] channel
         public void Dispose()
         {
             GC.SuppressFinalize(this);
+            Interlocked.Increment(ref s_MuxerDestroyCount);
             Close(!_isDisposed);
             sentinelConnection?.Dispose();
             var oldTimer = Interlocked.Exchange(ref sentinelPrimaryReconnectTimer, null);
@@ -2270,6 +2273,7 @@ public void Dispose()
         public async ValueTask DisposeAsync()
         {
             GC.SuppressFinalize(this);
+            Interlocked.Increment(ref s_MuxerDestroyCount);
             await CloseAsync(!_isDisposed).ForAwait();
             if (sentinelConnection is ConnectionMultiplexer sentinel)
             {

src/StackExchange.Redis/ExceptionFactory.cs

@@ -347,6 +347,12 @@ private static void AddCommonDetail(
                 Add(data, sb, "Last-Result-Bytes", "last-in", bs.Connection.BytesLastResult.ToString());
                 Add(data, sb, "Inbound-Buffer-Bytes", "cur-in", bs.Connection.BytesInBuffer.ToString());
 
+                var liveMuxers = ConnectionMultiplexer.GetLiveObjectCount(out var created, out var destroyed, out var nonDisposed);
+                if (created > 1)
+                {
+                    Add(data, sb, "Live-Multiplexers", "lm", $"{liveMuxers}/{created}/{destroyed}/{nonDisposed}");
+                }
+
                 Add(data, sb, "Sync-Ops", "sync-ops", multiplexer.syncOps.ToString());
                 Add(data, sb, "Async-Ops", "async-ops", multiplexer.asyncOps.ToString());