[ROOT 6.32] Vector of Pointers & Python

ROOT
1

Describe the bug

With ROOT 6.32, vector<TFormula*> seems to trigger a deallocation issue with Python.

Setup

ROOT v6.32.08
Built for linuxx8664gcc on Jan 24 2025, 09:37:12
From tags/v6-32-08@v6-32-08
With c++ (Ubuntu 13.3.0-6ubuntu2~24.04) 13.3.0

ROOT built from source:

$ root-config --features
cxx17 asimage builtin_clang builtin_cling builtin_fftw3 builtin_gsl builtin_gtest builtin_llvm builtin_nlohmannjson dataframe fftw3 mathmore pyroot roofit runtime_cxxmodules shared soversion sqlite x11 xml

To Reproduce

Please consider the following MWE: Files · raw_ptr · Uranie CEA / Prerequisites / Prerequisites Detection / Mini ROOT Library · GitLab

After loading ROOT, here are the steps to reproduce the error on Linux:

$ git clone -b raw_ptr https://gitlab.com/uranie-cea/prerequisites/prerequisites_detection/mini-root-library.git
$ mkdir build
$ cd build/

$ cmake -DCMAKE_INSTALL_PREFIX=install ../
$ cmake --build . --target install -j $(nproc)

$ ctest -V -R "builder_python"
[...]
4: ROOT: 6.32.08
4: trend: x
4:  *** Break *** segmentation violation
[...]
4: #7  0x00007d0d7d991100 in MiniLibrary::TGPBuilder::~TGPBuilder() () from /.../mini-root-library/build/install/lib/libTGPBuilder.so
4: #8  0x00007d0d7d992aca in ROOT::delete_MiniLibrarycLcLTGPBuilder(void*) () from /.../mini-root-library/build/install/lib/libTGPBuilder.so
4: #9  0x00007d0d6ade7835 in CPyCppyy::op_dealloc_nofree(CPyCppyy::CPPInstance*) () from /.../root/lib/libcppyy.so

Here are the definition & implementation of the class:

    class TGPBuilder {
    private:
        std::vector<TFormula*> _trends;
    public:
        TGPBuilder();
        ~TGPBuilder();
        std::vector<TFormula*> get_trends();
    };

MiniLibrary::TGPBuilder::TGPBuilder() {
    _trends.push_back(new TFormula("f", "x"));
}

MiniLibrary::TGPBuilder::~TGPBuilder() {
    for(auto& trend: _trends)
        delete trend;
    _trends.clear();
}

std::vector<TFormula*> MiniLibrary::TGPBuilder::get_trends() {
    return _trends;
}

And here is the test: test_builder.py · raw_ptr · Uranie CEA / Prerequisites / Prerequisites Detection / Mini ROOT Library · GitLab

import ROOT

print('ROOT:', ROOT.gROOT.GetVersion())
builder = ROOT.MiniLibrary.TGPBuilder()

for trend in builder.get_trends():
    print('trend:', trend.GetExpFormula())

Expected behavior

The test seems to pass with ROOT 6.34:

4: ROOT: 6.34.04
4: Print:
4: 	trend: x
4: Modification
4: Print:
4: 	trend: 
1/1 Test #4: builder_python ...................   Passed    0.70 sec

Solutions?

Which solutions do you recommand?

Using smart pointers seems to solve the issue: Files · shared_ptr · Uranie CEA / Prerequisites / Prerequisites Detection / Mini ROOT Library · GitLab

https://gitlab.com/uranie-cea/prerequisites/prerequisites_detection/mini-root-library/-/blob/shared_ptr/modeler/inc/TGPBuilder.h?ref_type=tags:

    class TGPBuilder {
    private:
        std::vector<std::shared_ptr<TFormula>> _trends;
    public:
        TGPBuilder();
        const std::vector<std::shared_ptr<TFormula>>& get_trends() const;
    };

https://gitlab.com/uranie-cea/prerequisites/prerequisites_detection/mini-root-library/-/blob/shared_ptr/modeler/src/TGPBuilder.cpp?ref_type=tags:

const std::vector<std::shared_ptr<TFormula>>& MiniLibrary::TGPBuilder::get_trends() const {
    return _trends;
}

$ git switch -d shared_ptr

[...]

$ ctest -V -R "builder_python"
[...]
4: ROOT: 6.32.08
4: Print:
4: 	trend: x
4: Modification
4: Print:
4: 	trend: 
1/1 Test #4: builder_python ...................   Passed    0.70 sec
2

Dear @Salomon,

let me add in the loop @vpadulan and @jonas.

Cheers,
Monica

1 Like
3

Dear @Salomon ,

Thanks for reaching out to the forum! Indeed, between 6.32 and 6.34 there have been improvements in the memory management on the Python side. Before analysing the branch diff, how difficult would it be for you to base your code directly on ROOT 6.34?

Cheers,
Vincenzo

4

Hello,

Thank you for your reply.

While testing migration to ROOT 6.34, I encountered issues on Windows (+ Boost).
I am discussing with the client to find solutions.

For the time being, with ROOT 6.32, I proposed to use a vector<TFormula> with a const& accessor, see modeler/inc/TGPBuilder.h · 1eb4c96cea9e11184a0360adc52c1b98b889e5da · Uranie CEA / Prerequisites / Prerequisites Detection / Mini ROOT Library · GitLab

5

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