[HDFS-4359] remove an unnecessary synchronized keyword in BPOfferService.java

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.0.2-alpha, 3.0.0-alpha1
• Fix Version/s: 2.0.3-alpha
• Component/s: datanode
• Target Version/s: 2.0.3-alpha
• Hadoop Flags: Reviewed
• Assignee: Liang Xie
• Reporter: Liang Xie
• Created: 04/Jan/13 03:26
• Updated: 12/May/16 18:12
• Resolved: 18/Jan/13 18:41

Description

we encountered a NN&DN hung issue, the DN hung was caused by no NN response for heartbeat. Per DN thread dump, i think we can have a little improvement on this detail code :

synchronized List<BPServiceActor> getBPServiceActors()

{ return Lists.newArrayList(bpServices); }

the bpServices is declared as :

private List<BPServiceActor> bpServices =
new CopyOnWriteArrayList<BPServiceActor>();

It's a thread-safe variant indead, so we can remove the above synchronized keyword safely, IMHO.

Here is a simple statistic for thread dump:
xieliang@xieliang:/tmp$ grep 0x00000007b00289f0 dn.jstack |wc -l
252