unexpected results for statement with closeOnCompletion

[shawjef3]

If a statement with closeOnCompletion() is executed a second time before its results have been consumed, it throws a NullPointerException. I am unsure what the appropriate error is, but it should be more descriptive. Something like, org.postgresql.util.PSQLException: Statement with closeOnCompletion can not be executed twice..

    val s = connection.prepareStatement("SELECT 1")
    s.closeOnCompletion()
    s.execute()
    s.execute()

The following, where I close the result set, throws org.postgresql.util.PSQLException: This statement has been closed., as I would expect.

    val s = connection.prepareStatement("SELECT 1")
    s.closeOnCompletion()
    s.executeQuery().close()
    s.execute()

[shawjef3]

The NullPointerException is thrown from PgStatement#closeForNextExecution(). Perhaps firstUnclosedResult is set to null from another thread after it is verified to be not null.

[lightswitch05]

I've recreated this same exception under different conditions using version 42.0.0. I have a generic getPreparedStatement function that calls closeOnCompletion() for all created statements. This is to help reduce any resource leakage. I then have a generic closeStatement function that attempts to always close a statement - called in all finally blocks. If I call statement.close(); on a statement that already has already had closeOnCompletion() called, then it always throws this exception, even if I check !statement.isClosed() first. The workaround is to also check !isCloseOnCompletion() before trying to close

Exception

java.lang.NullPointerException
        at org.postgresql.jdbc.PgStatement.closeForNextExecution(PgStatement.java:321)
        at org.postgresql.jdbc.PgStatement.close(PgStatement.java:603)
        at org.postgresql.jdbc.PgPreparedStatement.close(PgPreparedStatement.java:202)
        at com.<redacted>.closeStatement(<redacted>.java:73)

Example code

    protected PreparedStatement getPreparedStatement(final String sql) throws ConnectException {
        Connection connection = getConnection();
        PreparedStatement statement = null;
        try {
            statement = connection.prepareStatement(sql);
            statement.closeOnCompletion();
            return statement;
        } catch (SQLException ex) {
            this.closeStatement(statement);
            throw new ConnectException("Unable to get PreparedStatement.", ex);
        }
    }

    protected void closeStatement(final Statement statement) {
        try {
            if (statement != null && !statement.isClosed() && !statement.isCloseOnCompletion()) {
                // this close will cause the null pointer if I don't check isCloseOnCompletion first
                statement.close();
            }
        } catch (SQLException ex) {
            LOGGER.warning(String.format("Error closing statement: %s", ex.getMessage()));
        }
    }

[davecramer]

fixed by #1610