Updated

EonaCat.LogStack.LogClient/LogCentralClient.cs

@@ -86,6 +86,7 @@ namespace EonaCat.LogStack.LogClient
             entry.Properties = JsonHelper.ToJson(properties);
 
             _logQueue.Enqueue(entry);
+            TrimQueue();
 
             if (_logQueue.Count >= _options.BatchSize)
             {
@@ -93,6 +94,22 @@ namespace EonaCat.LogStack.LogClient
             }
         }
 
+        /// <summary>
+        /// Drops the oldest entries once the queue exceeds the configured maximum size,
+        /// so a server outage cannot grow the queue without bound.
+        /// </summary>
+        private void TrimQueue()
+        {
+            while (_logQueue.Count > _options.MaxQueueSize && _logQueue.TryDequeue(out _))
+            {
+            }
+        }
+
+        private bool IsExpired(LogEntry entry)
+        {
+            return DateTime.UtcNow - entry.Timestamp > _options.MaxRetention;
+        }
+
         private async Task FlushAsync()
         {
             if (_logQueue.IsEmpty)
@@ -106,6 +123,12 @@ namespace EonaCat.LogStack.LogClient
                 var batch = new List<LogEntry>();
                 while (batch.Count < _options.BatchSize && _logQueue.TryDequeue(out var entry))
                 {
+                    // Drop stale entries instead of holding/sending them indefinitely.
+                    if (IsExpired(entry))
+                    {
+                        continue;
+                    }
+
                     batch.Add(entry);
                 }
 
@@ -155,10 +178,17 @@ namespace EonaCat.LogStack.LogClient
                     Console.WriteLine($"[LogCentral] Failed to send logs to EonaCat: {ex.Message}");
                 }
 
+                // Only hold onto entries that are still within the retention window;
+                // never retry/re-queue indefinitely, and never exceed the max queue size.
                 foreach (var entry in batch)
                 {
-                    _logQueue.Enqueue(entry);
+                    if (!IsExpired(entry))
+                    {
+                        _logQueue.Enqueue(entry);
+                    }
                 }
+
+                TrimQueue();
             }
         }
 

EonaCat.LogStack.LogClient/LogCentralEonaCatAdapter.cs

@@ -17,6 +17,7 @@ namespace EonaCat.LogStack.LogClient
         public LogCentralEonaCatAdapter(LogBuilder logBuilder, LogCentralClient client)
         {
             _client = client;
+            _logBuilder = logBuilder ?? throw new ArgumentNullException(nameof(logBuilder));
             _logBuilder.OnLog += LogSettings_OnLog;
         }
 

EonaCat.LogStack.LogClient/LogCentralOptions.cs

@@ -17,5 +17,17 @@ namespace EonaCat.LogStack.LogClient
         public int BatchSize { get; set; } = 1;
         public int FlushIntervalSeconds { get; set; } = 5;
         public bool EnableFallbackLogging { get; set; } = true;
+
+        /// <summary>
+        /// Maximum number of entries kept in memory while the server is unreachable.
+        /// Oldest entries are dropped once this is exceeded to avoid unbounded memory growth.
+        /// </summary>
+        public int MaxQueueSize { get; set; } = 10000;
+
+        /// <summary>
+        /// Maximum time an entry is kept in memory waiting to be (re)sent. Entries older
+        /// than this are dropped instead of retried/re-queued forever.
+        /// </summary>
+        public TimeSpan MaxRetention { get; set; } = TimeSpan.FromMinutes(10);
     }
 }

EonaCat.LogStack/EonaCatLogger.cs

@@ -864,6 +864,7 @@ namespace EonaCat.LogStack
             // Request cancellation of the async pipeline if it's still running
             _asyncCts?.Cancel();
             _asyncCts?.Dispose();
+            _deadLetterQueue?.Dispose();
             GC.SuppressFinalize(this);
         }
     }

EonaCat.LogStack/EonaCatLoggerCore/DeadLetterQueue.cs

@@ -15,21 +15,53 @@ namespace EonaCat.LogStack.DeadLettering;
 /// Dead Letter Queue (DLQ) for capturing failed log attempts and enabling replay.
 /// Superior to data loss as it preserves logs that couldn't be delivered to any flow.
 /// </summary>
-public class DeadLetterQueue
+public class DeadLetterQueue : IDisposable
 {
     private readonly ConcurrentQueue<DeadLetterEvent> _queue = new ConcurrentQueue<DeadLetterEvent>();
     private readonly int _maxCapacity;
+    private readonly TimeSpan _maxRetention;
     private int _currentCount;
     private long _totalDropped;
     private long _totalEnqueued;
+    private long _totalExpired;
     private readonly object _statsLock = new object();
+    private bool _disposed;
 
     public event EventHandler<DeadLetterEvent> EventEnqueued;
     public event EventHandler<DeadLetterEventReplayed> EventReplayed;
 
-    public DeadLetterQueue(int maxCapacity = 100000)
+    /// <param name="maxCapacity">Maximum number of events held in memory.</param>
+    /// <param name="maxRetention">
+    /// Maximum time an undeliverable event is kept in memory before being dropped.
+    /// Defaults to 10 minutes so a persistently unreachable destination cannot cause
+    /// unbounded memory growth.
+    /// </param>
+    public DeadLetterQueue(int maxCapacity = 100000, TimeSpan? maxRetention = null)
     {
         _maxCapacity = Math.Max(1000, maxCapacity);
+        _maxRetention = maxRetention ?? TimeSpan.FromMinutes(10);
+    }
+
+    /// <summary>
+    /// Removes events that have exceeded the retention window. The queue is FIFO,
+    /// so the oldest entries are always at the front.
+    /// </summary>
+    private void PurgeExpired()
+    {
+        var now = DateTime.UtcNow;
+        while (_queue.TryPeek(out var oldest) && now - oldest.EnqueuedAt > _maxRetention)
+        {
+            if (!_queue.TryDequeue(out _))
+            {
+                break;
+            }
+
+            _currentCount--;
+            lock (_statsLock)
+            {
+                _totalExpired++;
+            }
+        }
     }
 
     /// <summary>
@@ -37,6 +69,7 @@ public class DeadLetterQueue
     /// </summary>
     public bool Enqueue(LogEvent logEvent, string failureReason, Exception failureException = null)
     {
+        PurgeExpired();
 
         if (_currentCount >= _maxCapacity)
         {
@@ -71,13 +104,18 @@ public class DeadLetterQueue
     /// <summary>
     /// Gets the count of events in the DLQ.
     /// </summary>
-    public int GetCount() => _currentCount;
+    public int GetCount()
+    {
+        PurgeExpired();
+        return _currentCount;
+    }
 
     /// <summary>
     /// Peeks at the next event without removing it.
     /// </summary>
     public bool TryPeek(out DeadLetterEvent dlEvent)
     {
+        PurgeExpired();
         return _queue.TryPeek(out dlEvent);
     }
 
@@ -86,6 +124,7 @@ public class DeadLetterQueue
     /// </summary>
     public bool TryDequeue(out DeadLetterEvent dlEvent)
     {
+        PurgeExpired();
         if (_queue.TryDequeue(out var evt))
         {
             _currentCount--;
@@ -102,6 +141,7 @@ public class DeadLetterQueue
     /// </summary>
     public List<DeadLetterEvent> GetAll(int skip = 0, int take = 100)
     {
+        PurgeExpired();
         return _queue.Skip(skip).Take(take).ToList();
     }
 
@@ -183,6 +223,7 @@ public class DeadLetterQueue
     /// </summary>
     public DeadLetterQueueStats GetStats()
     {
+        PurgeExpired();
         lock (_statsLock)
         {
             return new DeadLetterQueueStats
@@ -191,6 +232,7 @@ public class DeadLetterQueue
                 MaxCapacity = _maxCapacity,
                 TotalEnqueued = _totalEnqueued,
                 TotalDropped = _totalDropped,
+                TotalExpired = _totalExpired,
                 QueueUtilizationPercent = (_currentCount * 100.0) / _maxCapacity,
                 OldestEventAge = _queue.TryPeek(out var oldest) 
                     ? DateTime.UtcNow - oldest.EnqueuedAt 
@@ -199,6 +241,23 @@ public class DeadLetterQueue
         }
     }
 
+    /// <summary>
+    /// Clears the queue and releases event subscribers.
+    /// </summary>
+    public void Dispose()
+    {
+        if (_disposed)
+        {
+            return;
+        }
+
+        Clear();
+        EventEnqueued = null;
+        EventReplayed = null;
+        _disposed = true;
+        GC.SuppressFinalize(this);
+    }
+
     /// <summary>
     /// Gets events grouped by failure reason.
     /// </summary>
@@ -300,6 +359,11 @@ public class DeadLetterQueueStats
     /// </summary>
     public long TotalDropped { get; set; }
 
+    /// <summary>
+    /// Total events dropped for exceeding the retention window.
+    /// </summary>
+    public long TotalExpired { get; set; }
+
     /// <summary>
     /// Queue utilization as percentage.
     /// </summary>

EonaCat.LogStack/EonaCatLoggerCore/Exceptions/AdvancedExceptionRenderer.cs

@@ -241,23 +241,19 @@ public sealed class ExceptionContextBuilder
 /// </summary>
 public static class ExceptionContextManager
 {
-    private static readonly object _lock = new object();
+    // ConditionalWeakTable keys don't keep exceptions alive - entries are collected
-    private static readonly Dictionary<Exception, ExceptionContext> _contextMap = new();
+    // automatically once the exception itself is no longer referenced elsewhere,
+    // instead of accumulating forever in a regular static Dictionary.
+    // Not readonly: Clear() below swaps in a new instance (ConditionalWeakTable.Clear()
+    // isn't available on netstandard2.0/net4.8).
+    private static System.Runtime.CompilerServices.ConditionalWeakTable<Exception, ExceptionContext> _contextMap = new();
 
     /// <summary>
     /// Gets or creates context for an exception
     /// </summary>
     public static ExceptionContext GetOrCreateContext(Exception ex)
     {
-        lock (_lock)
+        return _contextMap.GetValue(ex, static _ => new ExceptionContext());
-        {
-            if (!_contextMap.TryGetValue(ex, out var context))
-            {
-                context = new ExceptionContext();
-                _contextMap[ex] = context;
-            }
-            return context;
-        }
     }
 
     /// <summary>
@@ -267,10 +263,8 @@ public static class ExceptionContextManager
     {
         var builder = ExceptionContext.Create();
         configure(builder);
-        lock (_lock)
+        _contextMap.Remove(ex);
-        {
+        _contextMap.Add(ex, builder.Build());
-            _contextMap[ex] = builder.Build();
-        }
         return ex;
     }
 
@@ -279,11 +273,7 @@ public static class ExceptionContextManager
     /// </summary>
     public static ExceptionContext? TryGetContext(Exception ex)
     {
-        lock (_lock)
+        return _contextMap.TryGetValue(ex, out var context) ? context : null;
-        {
-            _contextMap.TryGetValue(ex, out var context);
-            return context;
-        }
     }
 
     /// <summary>
@@ -291,10 +281,7 @@ public static class ExceptionContextManager
     /// </summary>
     public static void Clear()
     {
-        lock (_lock)
+        _contextMap = new System.Runtime.CompilerServices.ConditionalWeakTable<Exception, ExceptionContext>();
-        {
-            _contextMap.Clear();
-        }
     }
 }
 

EonaCat.LogStack/EonaCatLoggerCore/Flows/DiagnosticsFlow.cs

@@ -179,6 +179,7 @@ namespace EonaCat.LogStack.Flows
             _cts.Cancel();
             _samplerThread.Join(TimeSpan.FromSeconds(3));
             _cts.Dispose();
+            _proc.Dispose();
             await base.DisposeAsync().ConfigureAwait(false);
         }
 

EonaCat.LogStack/EonaCatLoggerCore/Flows/DlqFlow.cs

@@ -24,10 +24,11 @@ public class DlqFlow : FlowBase
     public DlqFlow(
         string name = "DLQ",
         LogLevel minimumLevel = LogLevel.Warning,
-        int maxCapacity = 100000)
+        int maxCapacity = 100000,
+        TimeSpan? maxRetention = null)
         : base(name, minimumLevel)
     {
-        _dlq = new DeadLetterQueue(maxCapacity);
+        _dlq = new DeadLetterQueue(maxCapacity, maxRetention);
     }
 
     /// <summary>
@@ -214,6 +215,8 @@ public class DlqFlow : FlowBase
             catch { }
         }
 
+        _dlq.Dispose();
+
         await base.DisposeAsync().ConfigureAwait(false);
     }
 }

EonaCat.LogStack/EonaCatLoggerCore/Flows/LokiFlow.cs

@@ -49,7 +49,9 @@ public sealed class LokiFlow : FlowBase
     private readonly Dictionary<string, string> _staticLabels;
     private readonly int _batchSize;
     private readonly TimeSpan _batchInterval;
-    private readonly ConcurrentQueue<(string Labels, string Line, long NanoTs)> _queue = new();
+    private readonly int _maxQueueSize;
+    private readonly TimeSpan _maxRetention;
+    private readonly ConcurrentQueue<(string Labels, string Line, long NanoTs, DateTime EnqueuedAt)> _queue = new();
     private readonly CancellationTokenSource _cts = new();
     private readonly Task _flushTask;
     private readonly SemaphoreSlim _batchSignal = new(0, int.MaxValue);
@@ -63,7 +65,9 @@ public sealed class LokiFlow : FlowBase
         string? basicUser = null,
         string? basicPassword = null,
         HttpClient? httpClient = null,
-        LogLevel minimumLevel = LogLevel.Trace)
+        LogLevel minimumLevel = LogLevel.Trace,
+        int maxQueueSize = 20000,
+        TimeSpan? maxRetention = null)
         : base("Loki", minimumLevel)
     {
         if (string.IsNullOrWhiteSpace(lokiUrl))
@@ -75,6 +79,10 @@ public sealed class LokiFlow : FlowBase
         _staticLabels = labels ?? new Dictionary<string, string>();
         _batchSize = batchSize > 0 ? batchSize : 50;
         _batchInterval = TimeSpan.FromMilliseconds(batchIntervalMs > 0 ? batchIntervalMs : 1000);
+        _maxQueueSize = maxQueueSize > 0 ? maxQueueSize : 20000;
+        // Never hold undeliverable data longer than this, to avoid unbounded memory growth
+        // when Loki is unreachable.
+        _maxRetention = maxRetention ?? TimeSpan.FromMinutes(10);
 
         if (httpClient != null)
         {
@@ -112,9 +120,16 @@ public sealed class LokiFlow : FlowBase
         var line    = BuildLine(logEvent);
         var nanoTs  = logEvent.Timestamp * 100L; // ticks → nanoseconds
 
-        _queue.Enqueue((labels, line, nanoTs));
+        _queue.Enqueue((labels, line, nanoTs, DateTime.UtcNow));
         Interlocked.Increment(ref BlastedCount);
 
+        // Drop oldest entries once over capacity so a slow/unreachable Loki instance
+        // cannot grow this queue without bound.
+        while (_queue.Count > _maxQueueSize && _queue.TryDequeue(out _))
+        {
+            Interlocked.Increment(ref DroppedCount);
+        }
+
         if (_queue.Count >= _batchSize)
         {
             _batchSignal.Release(1);
@@ -168,8 +183,16 @@ public sealed class LokiFlow : FlowBase
 
         // Group by label-set (Loki stream key)
         var groups = new Dictionary<string, List<(string Line, long NanoTs)>>(StringComparer.Ordinal);
+        var now = DateTime.UtcNow;
         while (_queue.TryDequeue(out var item))
         {
+            // Drop stale entries instead of holding/sending them indefinitely.
+            if (now - item.EnqueuedAt > _maxRetention)
+            {
+                Interlocked.Increment(ref DroppedCount);
+                continue;
+            }
+
             if (!groups.TryGetValue(item.Labels, out var list))
             {
                 list = new List<(string, long)>(16);

EonaCat.LogStack/EonaCatLoggerCore/MessageTemplate.cs

@@ -677,12 +677,21 @@ public sealed class MessageTemplate
     private static bool IsArgumentDriven(object?[] args) => args.Length > 0;
 
     // Template cache to avoid re-parsing the same strings
+    private const int MaxCacheSize = 5000;
     private static readonly System.Collections.Concurrent.ConcurrentDictionary<string, MessageTemplate> _cache
         = new(StringComparer.Ordinal);
 
     /// <summary>Returns a cached parsed template (recommended for hot paths).</summary>
-    public static MessageTemplate FromCache(string template) =>
+    public static MessageTemplate FromCache(string template)
-        _cache.GetOrAdd(template, static t => Parse(t));
+    {
+        // Guard against unbounded growth if callers pass many unique/dynamic template strings.
+        if (_cache.Count >= MaxCacheSize)
+        {
+            _cache.Clear();
+        }
+
+        return _cache.GetOrAdd(template, static t => Parse(t));
+    }
 
     /// <summary>Clears the template parse cache.</summary>
     public static void ClearCache() => _cache.Clear();

EonaCat.LogStack/Telemetry/TelemetryServer.cs

@@ -8,6 +8,7 @@ using System.Threading.Tasks;
 namespace EonaCat.LogStack.Telemetry;
 public sealed class TelemetryServer : IDisposable
 {
+    private const int MaxEvents = 5000;
     private readonly HttpListener _listener = new();
     public ConcurrentQueue<TelemetryEvent> Events { get; } = new();
     public int Count => Events.Count;
@@ -30,6 +31,10 @@ public sealed class TelemetryServer : IDisposable
                     if (item != null)
                     {
                         Events.Enqueue(item);
+                        // Drop the oldest events once capacity is exceeded to avoid unbounded growth.
+                        while (Events.Count > MaxEvents && Events.TryDequeue(out _))
+                        {
+                        }
                     }
                 }
                 else if (ctx.Request.Url?.AbsolutePath == "/")