remove memory fence

[VinInn]

avoid stalls due to memory fence.

[cmsbuild]

A new Pull Request was created by @VinInn (Vincenzo Innocente) for CMSSW_8_1_X.

It involves the following packages:

DataFormats/Common

@cmsbuild, @smuzaffar, @Dr15Jones, @davidlange6 can you please review it and eventually sign? Thanks.
@makortel, @wddgit, @wmtan this is something you requested to watch as well.
@slava77, @Degano, @smuzaffar you are the release manager for this.

cms-bot commands are list here #13028

[VinInn]

@cmsbuild , please test

[cmsbuild]

The tests are being triggered in jenkins.
https://cmssdt.cern.ch/jenkins/job/ib-any-integration/12371/console

[Dr15Jones]

+1
This works because these operations do not need the most up to date value of cachePtr_ to work correctly, they only need a guarantee to copy a value of cachePtr_ from some point in history. Also we do not need a memory fence since cachePtr_ is not being used as a synchronization barrier for any other memory location nor does it have to coordinate with the value from another std::atomic.

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_8_1_X IBs after it passes the integration tests. This pull request requires discussion in the ORP meeting before it's merged. @slava77, @davidlange6, @Degano, @smuzaffar

[cmsbuild]

-1

Tested at: b491ca1
I found errors in the following unit tests:

---> test runtestTqafTopEventSelection had ERRORS
---> test testRecoMETMETProducers had ERRORS

you can see the results of the tests here:
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-14070/12371/summary.html
'List

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-14070/12371/summary.html