How to properly end a DB session?

[jackzhp]

OrientDB Version: 2.2.18

Java Version: 1.8.0_131

OS: tomcat

Expected behavior

  when tomcat quits, In contextDestroyed, I call 
      pool.close();
  when tomcat starts, in contextInitialized, I call
       pool = new OPartitionedDatabasePool(url_DB, user_DB, password_DB);

I guess everything should quit properly, but I saw

Actual behavior

26-Apr-2017 09:43:16.618 WARNING [main] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [cS] appears to have started a thread named [Timer-0] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
java.lang.Object.wait(Native Method)
java.util.TimerThread.mainLoop(Timer.java:552)
java.util.TimerThread.run(Timer.java:505)
26-Apr-2017 09:43:16.619 WARNING [main] org.apache.catalina.loader.WebappClassLoaderBase.clearReferencesThreads The web application [cS] appears to have started a thread named [OrientDB <- Asynch Client (/192.168.1.18:2424)] but has failed to stop it. This is very likely to create a memory leak. Stack trace of thread:
java.net.SocketInputStream.socketRead0(Native Method)
java.net.SocketInputStream.socketRead(SocketInputStream.java:116)
java.net.SocketInputStream.read(SocketInputStream.java:171)
java.net.SocketInputStream.read(SocketInputStream.java:141)
java.io.BufferedInputStream.fill(BufferedInputStream.java:246)
java.io.BufferedInputStream.read(BufferedInputStream.java:265)
java.io.DataInputStream.readByte(DataInputStream.java:265)
com.orientechnologies.orient.enterprise.channel.binary.OChannelBinary.readByte(OChannelBinary.java:68)
com.orientechnologies.orient.client.binary.OChannelBinaryAsynchClient.beginResponse(OChannelBinaryAsynchClient.java:194)
com.orientechnologies.orient.client.binary.OAsynchChannelServiceThread.execute(OAsynchChannelServiceThread.java:55)
com.orientechnologies.common.thread.OSoftThread.run(OSoftThread.java:77)

Steps to reproduce

not needed.

Anyone has any idea about how to quit properly? thanks.