MySQL Bugs: #62518: Connector/J - Named Pipe connection cannot be closed

Bug #62518	Connector/J - Named Pipe connection cannot be closed
Submitted:	23 Sep 2011 17:10	Modified:	17 Nov 2011 14:37
Reporter:	Lucas Still	Email Updates:
Status:	Won't fix	Impact on me:	None
Category:	Connector / J	Severity:	S2 (Serious)
Version:	Community Server 5.5.15	OS:	Windows (7)
Assigned to:	Bogdan Degtyariov	CPU Architecture:	Any
Tags:	Connector/J, Named-Pipe

Description:
Windows 7
MySQL Community Server 5.5.15
Connector/J 5.1.17
Java 1.7.0

A named pipe connection can be made and used, but throws a warning on "close" and does not properly close the connection to the MySQL server. The following "warning" is thrown by the Connector/J Log:

Fri Sep 23 12:57:54 EDT 2011 WARN: Caught while disconnecting...

EXCEPTION STACK TRACE:

** BEGIN NESTED EXCEPTION ** 

java.net.SocketException
MESSAGE: Socket is not connected

STACKTRACE:

java.net.SocketException: Socket is not connected
	at java.net.Socket.shutdownInput(Socket.java:1456)
	at com.mysql.jdbc.MysqlIO.quit(MysqlIO.java:1687)
	at com.mysql.jdbc.ConnectionImpl.realClose(ConnectionImpl.java:4368)
	at com.mysql.jdbc.ConnectionImpl.close(ConnectionImpl.java:1557)
	at myprogram.main.main(main.java:41)

** END NESTED EXCEPTION **

---
Additionally, the MySQL server will display that the connection remains.

I wanted to establish a connection to a MySQL server using java, make a query, and then close the connection. I attempted each of these and was successful in the first two, but was unsuccessful in properly closing the connection. I expect the connection to be closed properly; i.e. without a warning and have the MySQL server terminate the connection.

How to repeat:
Create and run the following java program:

------------

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public final class main {
    public static void main(String[] args) {
        Connection conn = null;
        try {
            conn =
               DriverManager.getConnection("jdbc:mysql:///database?socketFactory=com.mysql.jdbc.NamedPipeSocketFactory&namedPipePath=\\\\.\\Pipe\\mysql.sock", "root", "password");

            conn.close();

           
        } catch (SQLException ex) {
            // handle any errors
            System.out.println("SQLException: " + ex.getMessage());
            System.out.println("SQLState: " + ex.getSQLState());
            System.out.println("VendorError: " + ex.getErrorCode());
        }
    }
}

------------

A SQLException will not be "caught", but the aforementioned warning will be printed and the connection to the MySQL server will persist until the java program terminates (in this case the program terminates immediately, but any variety of methods can be added/used to keep the program running).

Accidental severity selection corrected.

Verified using 5.1.18.
What is interesting - the database queries and results work as normal, it is just connection.close() failing.

Indeed. It isn't a game breaker, but I'm not positive about the compounding ramifications of failed closings.

Lucas, you are absolutely right. This must be fixed.

I don't think this is a driver bug. When one calls Connection.close(), it ends up calling Socket.close() on the socket in question. In this case, it's com.mysql.jdbc.NamedPipeSocket.

This does the following:

public synchronized void close() throws IOException {
			this.namedPipeFile.close();
			this.isClosed = true;
		}

If that's not enough to get the other end of the connection to "die", then there's not really much of anything that can be done from the driver side of things. It's either a JVM bug, or it's a Windows bug.

Is it that, or is the driver not properly keeping the socket "alive" so that it may be closed later? The only reason I ask this is because of the wording in the error message: "MESSAGE: Socket is not connected".

This would lead me to believe that the socket was already "killed" before .close() was even called.

This message is due to us trying to do Socket.shutdownInput(), which doesn't actually work on our socket wrapper around RandomAccessFile (which is why it's a warning).

Mark,

I tried debugging Connector/J and found one interesting thing, which might be helpful:

The method you named (com.mysql.jdbc.NamedPipeSocket.close()) is called after
the exception is thrown.

Here is the stack tracke for the exception:

java.net.SocketException: Socket is not connected
	at java.net.Socket.shutdownInput(Socket.java:1346)
	at com.mysql.jdbc.MysqlIO.quit(MysqlIO.java:1696)
	at com.mysql.jdbc.ConnectionImpl.realClose(ConnectionImpl.java:4371)
	at com.mysql.jdbc.ConnectionImpl.close(ConnectionImpl.java:1556)
	at bug62518.main(bug62518.java:24)

Here is the stack trace for the close() call, which actually closes the pipe:

Thread [main] (Suspended (breakpoint at line 64 in NamedPipeSocketFactory$NamedPipeSocket))	
	NamedPipeSocketFactory$NamedPipeSocket.close()(NamedPipeSocketFactory.java line: 64)
	MysqlIO.forceClose()(MysqlIO.java: 542)
	MysqlIO.quit()(MysqlIO.java: 1710) <-------------- pipe closure
	ConnectionImpl.realClose()(ConnectionImpl.java:4371)	
	ConnectionImpl.close()(ConnectionImpl.java:1556)	
	bug62518.main(String[])(bug62518.java:24)	

Maybe this.mysqlConnection.shutdownInput(); (MysqlIO.java:1696) should not be called at all for pipe connections and let forceClose(); (MysqlIO.java: 1710)
finish the job.

It's not an exception, it's a log message:

catch (IOException ioEx) {
                        this.connection.getLog().logWarn("Caught while disconnecting...", ioEx);
}

This doesn't prevent the close() of the underlying socket, and thus random access file in the named pipe's case from happening as far as I can see.

Thanks Mark, that makes sense. Have to try with C API client and see if a similar problem occurs.

MySQL C API client processed the pipe connect/disconnect quite well.
Indeed, mysql_close() function does not return any result or error.

Uploading the C test case below.

C test case

Attachment: bug62518.c (text/plain), 1.12 KiB.

Another test using C/NET showed no problems as well.

    private void button8_Click(object sender, EventArgs e)
    {
      using (MySqlConnection conn = new MySqlConnection(
       "server=.;protocol=pipe;database=test;User Id=*****;password=******"))
      {
        conn.Open();
        MessageBox.Show("Connection opened");

        // just to see that something is actually going on
        String SQL = "SHOW VARIABLES LIKE '%timeout'"; 
        using (MySqlCommand cmd = new MySqlCommand(SQL, conn))
        {
          cmd.CommandType = System.Data.CommandType.Text;
          MySqlDataReader dr = cmd.ExecuteReader();
          MessageBox.Show("Behold!!!!");

          String cnames = "";
          while (dr.Read())
          {
            cnames += dr[0] + " : " + dr[1] + "\r\n";
          }
          MessageBox.Show("Results: \r\n\r\n" + cnames);
        }
        conn.Close();
        MessageBox.Show("Closed!");
      }

    }

We can verify that close() is called on the underlying file descriptor, so we'll have to leave this chalked up to a JVM bug, unfortunately.

Bogdan, thanks for your efforts. Setting to "Won't Fix" as per Mark's comment.

Why not you just overwrite shutdownSocket() in the custom socket class, so it does nothing?