Xing Lin created HDFS-17067:
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             Summary: allowCoreThreadTimeOut should be set to true for 
nnProbingThreadPool in ObserverReadProxy
                 Key: HDFS-17067
                 URL: https://issues.apache.org/jira/browse/HDFS-17067
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: hdfs
    Affects Versions: 3.4.0
            Reporter: Xing Lin
            Assignee: Xing Lin


In HDFS-17030, we introduced an ExecutorService, to submit getHAServiceState() 
requests. We constructed the ExecutorService directly from a basic 
ThreadPoolExecutor, without setting _allowCoreThreadTimeOut_ to true. Then, the 
core thread will be kept up and running even when the main thread exits. To fix 
it, one could set _allowCoreThreadTimeOut_ to true. However, in this PR, we 
decide to directly use an existing executorService implementation 
(_BlockingThreadPoolExecutorService_) in hadoop instead. It takes care of 
setting _allowCoreThreadTimeOut_ and allowing setting the thread prefix.

Second minor issue is we did not shutdown the executorService in close(). It is 
a minor issue as close() will only be called when the garbage collector starts 
to reclaim an ObserverReadProxyProvider object, not when there is no reference 
to the ObserverReadProxyProvider object. The time between when an 
ObserverReadProxyProvider becomes dereferenced and when the garage collector 
actually starts to reclaim that object is out of control/under-defined (unless 
the program is shutdown with an explicit System.exit(1)).


{code:java}
  private final ExecutorService nnProbingThreadPool =
      new ThreadPoolExecutor(1, 4, 1L, TimeUnit.MINUTES,
          new ArrayBlockingQueue<Runnable>(1024));
{code}




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