Thread leakage when connection cannot be established

[krocodl]

During the execution of the next code we can observe a lost thread that will never end:

@Test
public void pureConnectionErrorTest() throws Exception {
    try {
        DriverManager.getConnection(DATABRICKS_JDBC_URL, DATABRICKS_USERNAME, DATABRICKS_PASSWORD + "!");
        fail();
    } catch (Exception ex) {
        // it is normal
    }
    while(true) {
        Thread.sleep(1000);
        System.out.println(".");
    }
}

This thread looks like the next:

"Connection evictor" #18 daemon prio=5 os_prio=31 cpu=0.10ms elapsed=7.05s tid=0x00007f9bd0925c00 nid=0x9603 waiting on condition [0x000000030ef7d000]
java.lang.Thread.State: TIMED_WAITING (sleeping)
at java.lang.Thread.sleep(java.base@17.0.3/Native Method)
at com.databricks.client.jdbc42.internal.apache.http.impl.client.IdleConnectionEvictor$1.run(IdleConnectionEvictor.java:66)
at java.lang.Thread.run(java.base@17.0.3/Thread.java:833)

It is lost, because method IdleConnectionEvictor#shutdown was not called.

Root exception:

Caused by: com.databricks.client.support.exceptions.ErrorException: [Databricks][DatabricksJDBCDriver](500593) Communication link failure. Failed to connect to server. Reason: HTTP Response code: 403, Error message: Unknown.
... 85 common frames omitted
Caused by: com.databricks.client.jdbc42.internal.apache.thrift.transport.TTransportException: HTTP Response code: 403, Error message: Unknown
at com.databricks.client.hivecommon.api.TETHttpClient.handleHeaderErrorMessage(Unknown Source)

[krocodl · Accepted solution]

I suspect, that you have to call 

TProtocol#getTransport().close()

 in case of catching exception inside 

HS2Client#openSession();

 In this case you have also rewrite TETHttpClient#close() in order to call ((ExtendedHttpClient)this.m_client).close(); in any cases.

After that my test started to work properly.

[krocodl · Accepted solution]

This issue is reported as fixed since v2.6.34. I validated version 

2.6.36

- it works normal. Many thanks to the developers for the work done!