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[core] Make TDirectory::Append tolerant to identical objects. #20888

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[core] Make TDirectory::Append tolerant to identical objects. #20888

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39ec151
[core] Make TDirectory::Append tolerant to identical objects.
hageboeck Sep 16, 2025
bea103b
[hist] Add a test for the interaction of TDirectory::Append and TH1.
hageboeck Jan 15, 2026
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31 changes: 23 additions & 8 deletions core/base/src/TDirectory.cxx
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Original file line number Diff line number Diff line change
Expand Up @@ -202,20 +202,35 @@ void TDirectory::Append(TObject *obj, Bool_t replace /* = kFALSE */)
{
if (!obj || !fList) return;

bool alreadyPresent = false;
if (replace && obj->GetName() && obj->GetName()[0]) {
TObject *old;
while (nullptr != (old = GetList()->FindObject(obj->GetName()))) {
Warning("Append","Replacing existing %s: %s (Potential memory leak).",
obj->IsA()->GetName(),obj->GetName());
ROOT::DirAutoAdd_t func = old->IsA()->GetDirectoryAutoAdd();
if (func) {
func(old,nullptr);
std::vector<TObject *> toRemoveList;
for (TObject *old : *GetList()) {
if (obj == old) {
if (alreadyPresent)
toRemoveList.push_back(obj);
else
alreadyPresent = true;
} else if (old->GetName() && strcmp(obj->GetName(), old->GetName()) == 0) {
toRemoveList.push_back(old);
Warning("Append", "Replacing existing %s: %s (Potential memory leak).", old->IsA()->GetName(),
old->GetName());
}
}

for (auto toRemove : toRemoveList) {
ROOT::DirAutoAdd_t func = toRemove->IsA()->GetDirectoryAutoAdd();
if (func && toRemove != obj) {
func(toRemove, nullptr);
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@pcanal pcanal Jan 16, 2026

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Last problem (which I don't think we can fix) is that if an histogram (that is not obj but has the same name as obj) is both in the current directory and is attached to a completely distinct TDirectory, this will result in that second histogram being removed from the other directory but not this one ....

On the other hand this would mean the user did:

TFile f1(...);
auto h1 = new TH1F("histo", ....);
TFile f2(...);
auto h2 = new TH1F("histo", ....);
f2.Append(h1);
f2.Append(h2, true);

If I read the code correctly, this would result in f1 being empty and f2 containing both histograms.

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@pcanal pcanal Jan 16, 2026 •
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Also related, if TH1::AddDirectoryStatus() is false, the function is a no-op :(
i.e. this 'fails':

TH1::AddDirectory(false);
TFile f1(...);
auto h1 = new TH1F("histo", ....);
h1.SetDirectory(&f1);
auto h2 = new TH1F("histo", ....);
f1.Append(h2, true);

} else {
Remove(old);
Remove(toRemove);
}
}
}

if (alreadyPresent)
return;

fList->Add(obj);
// A priori, a `TDirectory` object is assumed to not have shared ownership.
// If it is, let's rely on the user to update the bit.
Expand Down
28 changes: 28 additions & 0 deletions hist/hist/test/test_TH1.cxx
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Expand Up @@ -6,6 +6,9 @@
#include "TH1F.h"
#include "THLimitsFinder.h"

#include "TDirectory.h"
#include "TList.h"

#include <cmath>
#include <cstddef>
#include <random>
Expand Down Expand Up @@ -333,3 +336,28 @@ TEST(TH1L, SetBinContent)
h.SetBinContent(1, Large);
EXPECT_EQ(h.GetBinContent(1), Large);
}

TEST(TH1, InteractionWithTDirectoryAdd)
{
auto histo = std::make_unique<TH1F>("h", "h", 2, 0, 1);
auto tNamed = std::make_unique<TNamed>("h", "name clash");
auto tNamed2 = std::make_unique<TNamed>("h", "name clash 2");

auto dir = std::make_unique<TDirectory>("dir", "dir");
histo->SetDirectory(dir.get());
dir->Add(histo.get());
dir->Add(histo.get());
dir->Add(tNamed.get());
dir->Add(tNamed.get());
dir->Add(tNamed2.get());

EXPECT_EQ(histo->GetDirectory(), dir.get());

ROOT_EXPECT_WARNING_PARTIAL(dir->Add(histo.get(), /*replace=*/true), "Append", "Replacing existing TNamed");
EXPECT_EQ(histo->GetDirectory(), dir.get());
EXPECT_EQ(dir->GetList()->size(), 1);
EXPECT_EQ(dir->GetList()->First(), histo.get());

// Leave the ownership to the unique_ptrs
histo->SetDirectory(nullptr);
}
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