mutex

ClubDoorman/BadMessageManager.cs

@@ -6,7 +6,7 @@ namespace ClubDoorman;
 internal sealed class BadMessageManager
 {
     private const string Path = "data/bad-messages.txt";
-    private readonly SemaphoreSlim _semaphore = new(1);
+    private readonly SemaphoreSlim _fileLock = new(1);
 
     // with our data size, we would never need O(1), in fact if this ever bloats I'd rather limit this to ~2048 last messages
     // space savings are very moderate, base64 string takes up ~128 bytes while byte[] takes only 64, but then again it's
@@ -15,22 +15,31 @@ internal sealed class BadMessageManager
 
     public BadMessageManager()
     {
-        foreach (var item in File.ReadAllLines(Path))
-            _bad.Add(Convert.FromBase64String(item));
+        lock (_bad)
+        {
+            foreach (var item in File.ReadAllLines(Path))
+                _bad.Add(Convert.FromBase64String(item));
+        }
     }
 
-    public bool KnownBadMessage(string message) => _bad.Contains(ComputeHash(message));
+    public bool KnownBadMessage(string message)
+    {
+        lock (_bad)
+            return _bad.Contains(ComputeHash(message));
+    }
 
     public async ValueTask MarkAsBad(string message)
     {
         if (string.IsNullOrWhiteSpace(message))
             return;
         var hash = ComputeHash(message);
-        if (_bad.Add(hash))
-        {
-            using var token = await SemaphoreHelper.AwaitAsync(_semaphore);
-            await File.AppendAllLinesAsync(Path, [Convert.ToBase64String(hash)]);
-        }
+        bool added;
+        lock (_bad)
+            added = _bad.Add(hash);
+        if (!added)
+            return;
+        using var token = await SemaphoreHelper.AwaitAsync(_fileLock);
+        await File.AppendAllLinesAsync(Path, [Convert.ToBase64String(hash)]);
     }
 
     private static byte[] ComputeHash(string message) => SHA512.HashData(Encoding.UTF8.GetBytes(message));