[GitHub] [pulsar] lhotari commented on issue #17480: [Bug][Java client] main thread won't exit if not close pulsar client

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lhotari commented on issue #17480:
URL: https://github.com/apache/pulsar/issues/17480#issuecomment-1237979028

   > We (+ @yaalsn) discuss this, seems that netty has a shutdown hook to prevent client exit.
   
   Live non-daemon threads are a common reason why normal shutdown doesn't happen in a Java application.
   
   The [javadoc of java.lang.Thread](https://docs.oracle.com/javase/8/docs/api/java/lang/Thread.html):
   
   >  When a Java Virtual Machine starts up, there is usually a single non-daemon thread (which typically calls the method named main of some designated class). The Java Virtual Machine continues to execute threads until either of the following occurs:
   > 
   > * The exit method of class Runtime has been called and the security manager has permitted the exit operation to take place.
   > * All threads that are not daemon threads have died, either by returning from the call to the run method or by throwing an exception that propagates beyond the run method.
   
   I believe that Pulsar client creates threads that are non-daemon threads. This might be intentional. 
   I assume that it's better to handle the shutdown in a controlled way in any case. 
   A simple fix to your problem is to add a shutdown hook that calls `client.close()`. 
   
   @labuladong What is your actual use case? Could you share more of the scenario that you have in mind?
   


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