Dear colleagues,

It seems that there is an issue with writing ROOT files in G4AnalysisManager.

When updating the TTree in ROOT files generated by GEANT4, I faced the following situation:
- ROOT reported memory allocation problems and crashed.
- The ROOT File was corrupted and not readable anymore.

I traced the issue down with the ROOT developers.

The ROOT developers think that in G4AnalysisManager the list of free blocks is not set correctly. The evidence found by the ROOT developers is that by opening and closing the ROOT files the number of free blocks is modified (see below). 

After opening and closing the ROOT file without modifying it, my problems with memory and ROOT file corruption updating the TTree disappear.

TFile *file = new TFile("Cu_Bremsstrahlung.root","UPDATE")
gFile->GetListOfFree()->ls()
OBJ: TList      TList   Doubly linked list : 0
Free Segment: 4616147   4616212
Free Segment: 64        2000000000
file->Close()

TFile *file = new TFile("Cu_Bremsstrahlung.root","UPDATE")
gFile->GetListOfFree()->ls()
OBJ: TList      TList   Doubly linked list : 0
Free Segment: 4616347   2000000000

I should mention that I close the file properly with the G4AnalysisManager:

G4AnalysisManager* analysisManager = G4AnalysisManager::Instance();
analysisManager->SetVerboseLevel(4);
analysisManager->Write();
analysisManager->CloseFile();

Best regards,
Christian