[HDFS-1720] Federation: FSVolumeSet volumes is not synchronized correctly

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: Federation Branch
• Fix Version/s: Federation Branch
• Component/s: datanode
• Hadoop Flags: Reviewed
• Assignee: Suresh Srinivas
• Reporter: Suresh Srinivas
• Created: 03/Mar/11 21:09
• Updated: 09/Mar/11 08:47
• Resolved: 09/Mar/11 08:47

Description

Currently FSVolumeSet#volumes is package private and is exposed to outside classes:

1. Only some methods (such as FSVolumeSet#checkDirs()) are synchronized on FSVolumeSet.this. This method changes the
   content of the array (sets volumes with errors to null).
2. Some access to volumes are synchronized by FSDataset.this. Some access are not synchronized at all.

I propose making FSVolumeSet#unmodifiable list. This prevents accidental mutation from outside the class. The volumes
also are created anew when modifications are made.