[HDFS-9250] Add Precondition check to LocatedBlock#addCachedLoc

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.4.0
• Fix Version/s: 2.8.0, 3.0.0-alpha1
• Component/s: namenode
• Labels: supportability
• Target Version/s: 2.8.0
• Assignee: Xiao Chen
• Reporter: Xiao Chen
• Created: 15/Oct/15 17:47
• Updated: 30/Aug/16 01:25
• Resolved: 19/Oct/15 23:13

Description

We may see the following exception:

java.lang.ArrayStoreException
at java.util.ArrayList.toArray(ArrayList.java:389)
at org.apache.hadoop.hdfs.protocol.LocatedBlock.addCachedLoc(LocatedBlock.java:205)
at org.apache.hadoop.hdfs.server.namenode.CacheManager.setCachedLocations(CacheManager.java:907)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getBlockLocationsUpdateTimes(FSNamesystem.java:1974)
at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getBlockLocationsInt(FSNamesystem.java:1873)

The cause is that in LocatedBlock.java, when addCachedLoc:

• Passed in parameter loc, which is type DatanodeDescriptor, is added to cachedList
• cachedList was assigned to EMPTY_LOCS, which is type DatanodeInfoWithStorage.

Both DatanodeDescriptor and DatanodeInfoWithStorage are subclasses of DatanodeInfo but do not inherit from each other, resulting in the ArrayStoreException.