Fix thread-safety issue with StreamerInputSource

[Dr15Jones]

The previous way StreamerInputSource handled reading back RefCores
lead to the probability that when dereferenced the RefCore would read
from the wrong EventPrincipal when the job was using multiple streams
becuase it was reusing the same EventPrincipalHolder for each event.
The code has now been changed to make a new EventPrincipalHolder for
each event.

[cmsbuild]

A new Pull Request was created by @Dr15Jones (Chris Jones) for CMSSW_7_6_X.

Fix thread-safety issue with StreamerInputSource

It involves the following packages:

IOPool/Streamer

@cmsbuild, @smuzaffar, @Dr15Jones can you please review it and eventually sign? Thanks.
@wddgit, @wmtan this is something you requested to watch as well.
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@Degano you are the release manager for this.
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[Dr15Jones]

please test

[cmsbuild]

The tests are being triggered in jenkins.

[Dr15Jones]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_6_X IBs or unless it breaks tests. This pull request requires discussion in the ORP meeting before it's merged. @davidlange6, @Degano, @smuzaffar

[cmsbuild]

+1
Tested at: e263cbb
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-10856/7475/summary.html

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_6_X IBs (tests are also fine). This pull request requires discussion in the ORP meeting before it's merged. @davidlange6, @Degano, @smuzaffar

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-10856/7475/summary.html

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_6_X IBs (tests are also fine). This pull request requires discussion in the ORP meeting before it's merged. @davidlange6, @Degano, @smuzaffar

[davidlange6]

+1