Memory impact of un closed elasticsearch Client in Web application

Elastic Stack Elasticsearch
1

I am using Elasticsearch 1.5.1 and Tomcat 7. Web application creates a TCP client instance as Singleton during server startup through Spring Framework.

Just noticed that I failed to close the client during server shutdown. Through analysis on various tools like VisualVm, JConsole, MAT in Eclipse, it is evident that threads created by the elasticsearch client are live even after server(tomcat) shutdown.

Note: after introducing client.close() via Context Listener destroy methods, the threads are killed gracefully.

But my query here is,

  1. how to check the memory occupied by these live threads?
  2. Memory leak impact due to this thread?
    We have got few Out of memory:Perm gen errors in PROD. This might be a reason but still I would like to measure and provide stats for this.

Any suggestions/help please.