Hi Norbert,
You should be able to use TTrees with shared memory (TMapFile).
However, your TTree cannot be associated to a file. It must be
completely in memory. To create a TTree in memory, you can do:
solution 1
==========
gROOT->cd();
TTree *T = new TTree(......
solution 2
==========
TTree *T = new TTree(...
T->SetDirectory(0);
When you will invoke mfile->Update, a copy of the existing TTree
with all its branches/leaves/buffers/etc will be serialized
into the shared memory area.
For further info, see the class TMapFile.
For additional help, see directly with Fons.Rademakers@cern.ch
Rene Brun