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Segfault after remove and delete TChain friend


Hi all,

The following code block will cause a segfault (root 5.27 and gcc 4.1.2):

TChain* c1 = new TChain("data");
TChain* c2 = new TChain("cuts");


delete c2;


It seems c1 still has some reference to the branches in c2 even after the friend is removed (and it is removed from the ListOfFriends).

Until a bugfix happens, is there a reasonably convenient workaround? The use case is that my dataset is broken up into trees with interesting data and trees that are only really used to generate cuts. So I want to temporarily add the cut trees as friends just to generate a TEntryList, then get rid of them.



The following seems to get around the problem, by removing the friend from each of the chain’s subtrees, at least in my case:

Long64_t* offsets = parent->GetTreeOffset();
Long64_t entry = 0;
for(Int_t treenum=0; treenum < parent->GetNTrees(); ++treenum){
  entry += offsets[treenum];
  TTree* tree = parent->GetTree();

Not sure if it will work in all cases, but it would be nice to add this step to TChain::RemoveFriend.



Hi Ben,

This is corrected in the trunk (revision 46069) and in the v5-34 patch branch (v5.34/02 will be released at the end of the week and will include this fix).

Apriori to somewhat work around the problem you should just need:parent->GetTree()->RemoveFriend( friendChain->GetTree() );