RFR: 8234671: JFR api/consumer/recordingstream/TestStart.java failed due to timeout at testStartTwice()

[Erik Gahlin]

Hi,

Could I have a review of a fix that makes sure that an updated 
configuration for an event stream, for example an added handler for 
onEvent, is always discovered by the thread processing the events. Today 
it may go unnoticed, if it is added after RecordingStream::start has 
been invoked, which is what happens in TestStart.java

The implementation also changes so a Dispatcher object is only created 
if a change to the configuration has actually occurred.

Bug:
https://bugs.openjdk.java.net/browse/JDK-8234671

Webrev:
http://cr.openjdk.java.net/~egahlin/8234671/

Testing: jdk/jfr/* multiple times

Thanks
Erik