Clear connection pools on exit. Fixes #545

Author: bgrainger

src/MySqlConnector/Core/ConnectionPool.cs

@@ -517,6 +517,16 @@ public ConnectionStringPool(string connectionString, ConnectionPool pool)
 			public ConnectionPool Pool { get; }
 		}
 
+#if !NETSTANDARD1_3
+		static ConnectionPool()
+		{
+			AppDomain.CurrentDomain.DomainUnload += OnAppDomainShutDown;
+			AppDomain.CurrentDomain.ProcessExit += OnAppDomainShutDown;
+		}
+
+		static void OnAppDomainShutDown(object sender, EventArgs e) => ClearPoolsAsync(IOBehavior.Synchronous, CancellationToken.None).GetAwaiter().GetResult();
+#endif
+
 		static readonly IMySqlConnectorLogger Log = MySqlConnectorLogManager.CreateLogger(nameof(ConnectionPool));
 		static readonly ConcurrentDictionary<string, ConnectionPool> s_pools = new ConcurrentDictionary<string, ConnectionPool>();