As noted above, the goal is to replace LazyGetter/LazyRef that thread safe are not.
this bool does not add/remove anything to the thread-safety of this class.
edmNew:DetSetVector is in use in reco since long time. it is fully thread safe for what reco is concerned.
Thread safety issues exits in the current desing/implementaion/use of the OnDemandTracker that is currently based on LazyGetter/LazyRef Mechanism shared with Ecal.
Ecal will most probably move away (for efficiency reasons) from OnDemand unpacking.
In Tracking we plan to get way from LazyGetter/LazyRef (and this PR paves the way to it) and then attack the issues of concurrency in tracking in particular at HLT. This will be done on a unified design/implementation offline/online.
For that we need to use edmNew::DetsetVector for both offline and online use.