Refresh message statistics after tracking messages in a background thread

app/Server/Database/Sqlite/SqliteDatabaseFile.cs

@@ -36,10 +36,13 @@ namespace DHT.Server.Database.Sqlite {
 
 		private readonly Log log;
 		private readonly SqliteConnectionPool pool;
+		private readonly SqliteMessageStatisticsThread messageStatisticsThread;
 
 		private SqliteDatabaseFile(string path, SqliteConnectionPool pool) {
 			this.log = Log.ForType(typeof(SqliteDatabaseFile), System.IO.Path.GetFileName(path));
 			this.pool = pool;
+			this.messageStatisticsThread = new SqliteMessageStatisticsThread(pool, UpdateMessageStatistics);
+
 			this.Path = path;
 			this.Statistics = new DatabaseStatistics();
 
@@ -51,6 +54,7 @@ namespace DHT.Server.Database.Sqlite {
 		}
 
 		public void Dispose() {
+			messageStatisticsThread.Dispose();
 			pool.Dispose();
 		}
 
@@ -299,7 +303,7 @@ namespace DHT.Server.Database.Sqlite {
 			}
 
 			tx.Commit();
-			UpdateMessageStatistics(conn);
+			messageStatisticsThread.RequestUpdate();
 		}
 
 		public int CountMessages(MessageFilter? filter = null) {

app/Server/Database/Sqlite/SqliteMessageStatisticsThread.cs

@@ -0,0 +1,54 @@
+using System;
+using System.Threading;
+using DHT.Server.Database.Sqlite.Utils;
+
+namespace DHT.Server.Database.Sqlite {
+	sealed class SqliteMessageStatisticsThread : IDisposable {
+		private readonly SqliteConnectionPool pool;
+		private readonly Action<ISqliteConnection> action;
+		
+		private readonly CancellationTokenSource cancellationTokenSource = new();
+		private readonly CancellationToken cancellationToken;
+		
+		private readonly AutoResetEvent requestEvent = new (false);
+
+		public SqliteMessageStatisticsThread(SqliteConnectionPool pool, Action<ISqliteConnection> action) {
+			this.pool = pool;
+			this.action = action;
+			
+			this.cancellationToken = cancellationTokenSource.Token;
+			
+			var thread = new Thread(RunThread) {
+				Name = "DHT message statistics thread",
+				IsBackground = true
+			};
+			thread.Start();
+		}
+
+		public void Dispose() {
+			try {
+				cancellationTokenSource.Cancel();
+			} catch (ObjectDisposedException) {}
+		}
+
+		public void RequestUpdate() {
+			try {
+				requestEvent.Set();
+			} catch (ObjectDisposedException) {}
+		}
+
+		private void RunThread() {
+			try {
+				while (!cancellationToken.IsCancellationRequested) {
+					if (requestEvent.WaitOne(TimeSpan.FromMilliseconds(100))) {
+						using var conn = pool.Take();
+						action(conn);
+					}
+				}
+			} finally {
+				cancellationTokenSource.Dispose();
+				requestEvent.Dispose();
+			}
+		}
+	}
+}