[#CONJ-25] Connection cannot be closed without closing a resultset if fetching is not done, close() hangs

I think it's a minor issue because JDBC does not explicitly state that Connection.close() must close a statement and result sets; but in the current state it's particularly error-prone, and hanging isn't good, so if it's possible, it would be good to fix. MySQL Connector/J doesn't show this problem.

The following test case sets a non-zero fetch size for a statement and then executes a query with a sizable enough result set. Before all values are fetched, the connection gets closed, but the operation never ends.

import java.sql.DriverManager;

import java.sql.Connection;

import java.sql.Statement;

import java.sql.ResultSet;

public class NonFinishedFetch

  public static void main (String argv[]) throws Exception

    try {

      String dsn = "jdbc:mysql://localhost:3306/test?user=root";

      Statement stmt = null;

      ResultSet rs = null;

      Connection conn = DriverManager.getConnection(dsn);

      stmt = conn.createStatement();

      stmt.execute("DROP TABLE IF EXISTS t1");

      stmt.execute("CREATE TABLE t1 (a VARCHAR(1024))");

      String st = "INSERT INTO t1 VALUES (REPEAT('a',1024))";

      for ( int i=1; i<=100; i++) {

        st = st + ",(REPEAT('a',1024))";

      stmt.setFetchSize(Integer.MIN_VALUE);

      stmt.execute(st);

      rs = stmt.executeQuery("SELECT * FROM t1 a, t1 b");

      conn.close();

    } catch (Exception e) {

      e.printStackTrace();

Full thread dump OpenJDK 64-Bit Server VM (20.0-b12 mixed mode):

"Attach Listener" daemon prio=10 tid=0x0000000001afe000 nid=0x2089 runnable [0x0000000000000000]

   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:

	- None

"Low Memory Detector" daemon prio=10 tid=0x0000000001a0b800 nid=0x2079 runnable [0x0000000000000000]

   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:

	- None

"C2 CompilerThread1" daemon prio=10 tid=0x0000000001a06800 nid=0x2078 waiting on condition [0x0000000000000000]

   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:

	- None

"C2 CompilerThread0" daemon prio=10 tid=0x0000000001a03800 nid=0x2077 waiting on condition [0x0000000000000000]

   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:

	- None

"Signal Dispatcher" daemon prio=10 tid=0x0000000001a02800 nid=0x2076 runnable [0x0000000000000000]

   java.lang.Thread.State: RUNNABLE

   Locked ownable synchronizers:

	- None

"Finalizer" daemon prio=10 tid=0x00000000019e3800 nid=0x2075 in Object.wait() [0x00007f8985d2f000]

   java.lang.Thread.State: WAITING (on object monitor)

	at java.lang.Object.wait(Native Method)

	- waiting on <0x00000000ec7782c0> (a java.lang.ref.ReferenceQueue$Lock)

	at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:133)

	- locked <0x00000000ec7782c0> (a java.lang.ref.ReferenceQueue$Lock)

	at java.lang.ref.ReferenceQueue.remove(ReferenceQueue.java:149)

	at java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:177)

   Locked ownable synchronizers:

	- None

"Reference Handler" daemon prio=10 tid=0x00000000019dc000 nid=0x2074 in Object.wait() [0x00007f8985e30000]

   java.lang.Thread.State: WAITING (on object monitor)

	at java.lang.Object.wait(Native Method)

	- waiting on <0x00000000ec778360> (a java.lang.ref.Reference$Lock)

	at java.lang.Object.wait(Object.java:502)

	at java.lang.ref.Reference$ReferenceHandler.run(Reference.java:133)

	- locked <0x00000000ec778360> (a java.lang.ref.Reference$Lock)

   Locked ownable synchronizers:

	- None

"main" prio=10 tid=0x0000000001971800 nid=0x2070 runnable [0x00007f898cbd8000]

   java.lang.Thread.State: RUNNABLE

	at java.net.SocketInputStream.socketRead0(Native Method)

	at java.net.SocketInputStream.read(SocketInputStream.java:146)

	at java.net.SocketInputStream.read(SocketInputStream.java:199)

	at org.mariadb.jdbc.internal.mysql.MySQLProtocol.close(MySQLProtocol.java:563)

	at org.mariadb.jdbc.internal.mysql.MySQLProtocol.close(MySQLProtocol.java:589)

	at org.mariadb.jdbc.MySQLConnection.close(MySQLConnection.java:257)

	at NonFinishedFetch.main(NonFinishedFetch.java:27)

   Locked ownable synchronizers:

	- None

"VM Thread" prio=10 tid=0x00000000019d5000 nid=0x2073 runnable

"GC task thread#0 (ParallelGC)" prio=10 tid=0x000000000197c800 nid=0x2071 runnable

"GC task thread#1 (ParallelGC)" prio=10 tid=0x000000000197e000 nid=0x2072 runnable

"VM Periodic Task Thread" prio=10 tid=0x0000000001a0e000 nid=0x207a waiting on condition

JNI global references: 885

[CONJ-25] Connection cannot be closed without closing a resultset if fetching is not done, close() hangs Created: 2013-02-14 Updated: 2013-02-14 Resolved: 2013-02-14
Status:	Closed
Project:	MariaDB Connector/J
Component/s:	None
Affects Version/s:	1.1.0
Fix Version/s:	1.1.1

[CONJ-25] Connection cannot be closed without closing a resultset if fetching is not done, close() hangs Created: 2013-02-14 Updated: 2013-02-14 Resolved: 2013-02-14