Handle QueryInterrupted exceptions when canceling completed queries.

KILL QUERY will interrupt a subsequent query if the command it was intended to cancel has already completed, and the connection is idle. In order to handle this case, we issue a dummy query to catch the QueryInterrupted exception. See https://bugs.mysql.com/bug.php?id=45679.

Author: adampoit

src/MySqlConnector/MySqlClient/MySqlCommand.cs

@@ -66,6 +66,7 @@ public override void Prepare()
 
 		public override string CommandText { get; set; }
 		public override int CommandTimeout { get; set; }
+		public bool	IsCanceled { get; internal set; }
 
 		public override CommandType CommandType
 		{

src/MySqlConnector/MySqlClient/MySqlDataReader.cs

@@ -287,6 +287,24 @@ private void DoClose()
 				var connection = Command.Connection;
 				if (!connection.BufferResultSets)
 					connection.Session.FinishQuerying();
+
+				if (Command.IsCanceled)
+				{
+					// KILL QUERY will kill a subsequent query if the command it was intended to cancel has already completed.
+					// In order to handle this case, we issue a dummy query to catch the QueryInterrupted exception.
+					// See https://bugs.mysql.com/bug.php?id=45679
+					var killClearCommand = new MySqlCommand("SELECT * FROM fake_table LIMIT 0;", connection);
+					try
+					{
+						killClearCommand.ExecuteReader();
+					}
+					catch (MySqlException ex)
+					{
+						if (ex.Number != (int) MySqlErrorCode.QueryInterrupted && ex.Number != (int) MySqlErrorCode.NoSuchTable)
+							throw;
+					}
+				}
+
 				Command.ReaderClosed();
 				if ((m_behavior & CommandBehavior.CloseConnection) != 0)
 				{

src/MySqlConnector/Serialization/MySqlSession.cs

@@ -84,6 +84,8 @@ public void DoCancel(MySqlCommand commandToCancel, MySqlCommand killCommand)
 				// blocking the other thread for an extended duration.
 				killCommand.CommandTimeout = 3;
 				killCommand.ExecuteNonQuery();
+
+				commandToCancel.IsCanceled = true;
 			}
 		}
 

tests/SideBySide/CancelTests.cs

@@ -228,6 +228,18 @@ public async Task CancelCommandWithTokenBeforeExecuteReader()
 			}
 		}
 
+		[Fact]
+		public async Task CancelCompletedCommand()
+		{
+			using (var cmd = m_database.Connection.CreateCommand())
+			{
+				cmd.CommandText = @"select 1;";
+
+				using (await cmd.ExecuteReaderAsync().ConfigureAwait(false))
+					cmd.Cancel();
+			}
+		}
+
 		[UnbufferedResultSetsFact]
 		public async Task CancelHugeQueryWithTokenAfterExecuteReader()
 		{