Merge pull request #5465 from tui-cs/copilot/fix-memory-leak

Bound UICatalog in-memory log capture to stop long-run memory growth

Author: tig

Examples/UICatalog/ScenarioLogCapture.cs

@@ -10,6 +10,9 @@ namespace UICatalog;
 /// </summary>
 public class ScenarioLogCapture : ILoggerProvider
 {
+    private const int MaxBufferChars = 256_000;
+    private const int TrimTargetChars = 192_000;
+
     private readonly object _lock = new ();
     private readonly StringBuilder _buffer = new ();
 
@@ -113,6 +116,7 @@ internal void Log (LogLevel logLevel, string message)
         lock (_lock)
         {
             _buffer.AppendLine ($"[{logLevel}] {message}");
+            TrimIfNeeded ();
 
             if (logLevel >= LogLevel.Error)
             {
@@ -121,6 +125,40 @@ internal void Log (LogLevel logLevel, string message)
         }
     }
 
+    private void TrimIfNeeded ()
+    {
+        if (_buffer.Length <= MaxBufferChars)
+        {
+            return;
+        }
+
+        var removeCount = _buffer.Length - TrimTargetChars;
+
+        if (removeCount <= 0)
+        {
+            return;
+        }
+
+        int nextLineBreak = -1;
+
+        for (int i = removeCount; i < _buffer.Length; i++)
+        {
+            if (_buffer [i] == '\n')
+            {
+                nextLineBreak = i;
+                break;
+            }
+        }
+
+        if (nextLineBreak >= 0)
+        {
+            removeCount = nextLineBreak + 1;
+        }
+
+        _buffer.Remove (0, removeCount);
+        _scenarioStartPosition = Math.Max (0, _scenarioStartPosition - removeCount);
+    }
+
     /// <inheritdoc />
     public void Dispose ()
     {

Tests/IntegrationTests/ScenarioLogCaptureTests.cs

@@ -0,0 +1,66 @@
+using Microsoft.Extensions.Logging;
+using UICatalog;
+
+namespace IntegrationTests;
+
+public class ScenarioLogCaptureTests
+{
+    [Fact]
+    public void LogBuffer_IsTrimmed_WhenItGrowsTooLarge ()
+    {
+        ScenarioLogCapture capture = new ();
+        ILogger logger = capture.CreateLogger ("test");
+        string message = new ('x', 4096);
+
+        for (var i = 0; i < 120; i++)
+        {
+            logger.LogInformation ("{Message}", message);
+        }
+
+        Assert.True (capture.GetAllLogs ().Length <= 256_000);
+    }
+
+    [Fact]
+    public void GetScenarioLogs_RespectsScenarioStart_AfterTrim ()
+    {
+        ScenarioLogCapture capture = new ();
+        ILogger logger = capture.CreateLogger ("test");
+        string message = new ('y', 4096);
+
+        // Fill close to the cap so the next few entries will trigger a trim.
+        while (capture.GetAllLogs ().Length < 250_000)
+        {
+            logger.LogInformation ("{Message}", message);
+        }
+
+        logger.LogInformation ("before-start");
+
+        capture.MarkScenarioStart ();
+
+        int lengthBefore = capture.GetAllLogs ().Length;
+        bool trimmed = false;
+
+        for (int i = 0; i < 50; i++)
+        {
+            logger.LogInformation ("{Message}", message);
+
+            int lengthAfter = capture.GetAllLogs ().Length;
+
+            if (lengthAfter < lengthBefore)
+            {
+                trimmed = true;
+                break;
+            }
+
+            lengthBefore = lengthAfter;
+        }
+
+        Assert.True (trimmed);
+
+        logger.LogInformation ("after-start");
+
+        string logs = capture.GetScenarioLogs ();
+        Assert.DoesNotContain ("before-start", logs);
+        Assert.Contains ("after-start", logs);
+    }
+}