Double free when making copies of a distributed tree

[dalg24]

This occurred to me when reviewing ECP-copa/Cabana#295
The implicitly-declared copy constructor and copy assignment operator are problematic because they make copies of the communicator data member and when an object gets out of scope MPI_Comm_free gets called on it.

ArborX/src/ArborX_DistributedSearchTree.hpp

Line 45 in 4834bff

~DistributedSearchTree() { MPI_Comm_free(&_comm); }

[aprokop]

This is not the only problem from copying communicators. If a user copies a distributed tree, then the MPI calls and requests from different trees may overlap, potentially resulting in undefined behavior and/or deadlocks.

The fix is straightforward: copy constructor and copy assignment operators must duplicate the communicator.

[masterleinad]

Time for https://clang.llvm.org/extra/clang-tidy/checks/cppcoreguidelines-special-member-functions.html?

[aprokop]

Time for https://clang.llvm.org/extra/clang-tidy/checks/cppcoreguidelines-special-member-functions.html?

Good suggestion, but maybe overkill for now.

[masterleinad]

Why overkill? Isn't thinking about copy/move semantics worth it?

[aprokop]

@masterleinad Probably not. I would rather not get distracted by possibly multiple places to get spotted by the tool at the moment. But it could be interesting to just post the results of it here just to see where we are at.