David Mollitor created HDFS-14864:
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Summary: DatanodeDescriptor Use Concurrent BlockingQueue
Key: HDFS-14864
URL: https://issues.apache.org/jira/browse/HDFS-14864
Project: Hadoop HDFS
Issue Type: Improvement
Components: namenode
Affects Versions: 3.2.0
Reporter: David Mollitor
Assignee: David Mollitor
https://github.com/apache/hadoop/blob/trunk/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/DatanodeDescriptor.java#L104-L106
This collection needs to be thread safe and it needs to repeatedly poll the
queue to drain it, so use {{BlockingQueue}} which has a {{drain()}} method just
for this purpose:
{quote}
This operation may be more efficient than repeatedly polling this queue.
{quote}
[https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/BlockingQueue.html#drainTo(java.util.Collection,%20int)]
Also, the collection returns 'null' if there is nothing to drain from the
queue. This is a confusing and error-prone affect. It should just return an
empty list. I've also updated the code to be more consistent and to return a
java {{List}} in all places instead of a {{List}} in some and a native array in
others. This will make the entire usage much more consistent and safe.
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