Establishing multiple connections in parallel can throw an IndexOutOfBoundsException

[Chrriis]

Driver version

11.1.2

Problem description

At startup, we create many connections in parallel to many servers to check their status/versions. Occasionally, with this version of the driver, we get an exception:

Exception in thread "ConfigDatabaseData - get rights from DB" java.lang.IndexOutOfBoundsException: Index 0 out of bounds for length 0
	at java.base/jdk.internal.util.Preconditions.outOfBounds(Preconditions.java:64)
	at java.base/jdk.internal.util.Preconditions.outOfBoundsCheckIndex(Preconditions.java:70)
	at java.base/jdk.internal.util.Preconditions.checkIndex(Preconditions.java:266)
	at java.base/java.util.Objects.checkIndex(Objects.java:359)
	at java.base/java.util.ArrayList.get(ArrayList.java:427)
	at com.microsoft.sqlserver.jdbc/com.microsoft.sqlserver.jdbc.SocketFinder.getInetAddressByIPPreference(IOBuffer.java:2710)
	at com.microsoft.sqlserver.jdbc/com.microsoft.sqlserver.jdbc.SocketFinder.getSocketByIPPreference(IOBuffer.java:2753)
	at com.microsoft.sqlserver.jdbc/com.microsoft.sqlserver.jdbc.SocketFinder.findSocket(IOBuffer.java:2399)
	at com.microsoft.sqlserver.jdbc/com.microsoft.sqlserver.jdbc.TDSChannel.open(IOBuffer.java:766)
	at com.microsoft.sqlserver.jdbc/com.microsoft.sqlserver.jdbc.SQLServerConnection.connectHelper(SQLServerConnection.java:3298)
	at com.microsoft.sqlserver.jdbc/com.microsoft.sqlserver.jdbc.SQLServerConnection.login(SQLServerConnection.java:2948)
	at com.microsoft.sqlserver.jdbc/com.microsoft.sqlserver.jdbc.SQLServerConnection.connectInternal(SQLServerConnection.java:2788)
	at com.microsoft.sqlserver.jdbc/com.microsoft.sqlserver.jdbc.SQLServerConnection.connect(SQLServerConnection.java:1661)
	at com.microsoft.sqlserver.jdbc/com.microsoft.sqlserver.jdbc.SQLServerDriver.connect(SQLServerDriver.java:1067)
	at java.sql/java.sql.DriverManager.getConnection(DriverManager.java:681)

It seems that access to "addressList" in "IOBuffer" is not synchronized and it is mutated by some of the connections.

I am happy to help testing fixes if you cannot easily reproduce the issue (although the DLL issue #1850 is a bit of a pain for our setup).

[Chrriis]

Here is a self-contained example:

public class TestMsSqlJdbcParallelConnections {
    public static void main(String[] args) throws Exception {
        Class.forName(com.microsoft.sqlserver.jdbc.SQLServerDriver.class.getName());
        String connectionString = "jdbc:sqlserver://?databaseName=xxxxx;serverName=localhost;userName=xxxxx;password=xxxxx;instanceName=SQLEXPRESS;packetSize=16384;prepareMethod=prepare;trustServerCertificate=true";
        for(int i=0; i<100; i++) {
            new Thread() {
                @Override
                public void run() {
                    try {
                        Connection conn = DriverManager.getConnection(connectionString);
                        conn.close();
                    } catch (SQLException e) {
                    }
                }
            }.start();
        }
    }
}

Simply change the "xxxxx" with proper data so that it actually works. Perhaps the fact that the database is on localhost on a fast machine makes the problem appear more often: with the above I get the error on 3 out of 4 runs.

[tkyc]

Hey @Chrriis, thanks for reporting this. We'll look into this issue.