events in EventDispatcherImpl should be volatile since it is expected to be modified by different threads

Just like queue in PipelineOrchestratorImpl, events in EventDispatcherImpl should be volatile since it is expected to be modified by different threads.

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Ref gerrit in which Madhu fixes a similar issue in PipelineOrchestratorImpl:
https://git.opendaylight.org/gerrit/#/c/10843/

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[07:32:22] <flaviof> Madhu: don't u need to make queue volatile ?

[07:32:43] <@Madhu> flaviof: why ?

[07:32:47] <flaviof> bc there are 2 threads using it in your case

[07:33:03] <@Madhu> well... yes it is preferred

[07:33:13] <@Madhu> flaviof: but not mandatory i hope

[07:33:20] <@Madhu> in that case.... EventDispatcherImpl is in trouble too

[07:33:42] <dave_tucker> Madhu well there could be a case where the queue has been updated but it's not visible to the other thread

[07:33:53] <dave_tucker> hence volatile would make perfect sense here

[07:33:56] <@Madhu> dave_tucker: what case is that ?

[07:34:06] <@Madhu> dave_tucker: yep agreed. volatile make sense

[07:34:13] dave_tucker looks to code for answers

[07:34:26] <@Madhu> but am still trying to understand why EventDispatcherImpl works

[07:34:54] <@Madhu> dave_tucker: flaviof could it be because am using a "String" Object ?

[07:35:01] <dave_tucker> Madhu i was thinking that

[07:35:02] Madhu remembers String Objects are special in java

[07:35:12] <flaviof> Madhu: you are right, i dnot know how/why eventDispatcher does not suffer from the same disease

[07:35:45] <@Madhu> flaviof: dave_tucker but i agree having volatile is good to have.