A fundamental feature of TDF is that the interface can be used with implicit parallelism enabled or disabled in an identical way. If
ROOT-8753 is achieved, the write out must work also in the MT case.
Unfortunately at the moment it is not possible to write a single tree from different threads. This situation clearly needs improvement.
The idea is to leverage, if possible, the TThreadMergingFile/Server* which is part of GeantV.
The work will start with the creation of an example using that infrastructure independent of the TDF. Once the mechanism is under control, it will be integrated with the SnapShot instant action.
This item is under the umbrella of TDF even if it is meant to evolve into a proper integration into ROOT.