Unresolved reference when using concurrent_hash_map

[IvanSavenko]

Summary

Class hash_map_iterator (accessed for example via concurrent_hash_map::begin method) provides operator- which does not seems to be defined anywhere leading to linking error

Version

onetbb 2021.5.0 (as provided by Ubuntu 24.04). Same behavior was observed on 2022.3.0

Environment

• Ubuntu 24.04
• gcc 13.3

Observed Behavior

Linking fails with:

/usr/bin/ld: CMakeFiles/test_tbb_app.dir/main.cpp.o: in function `main':
main.cpp:(.text+0x75): undefined reference to `long tbb::detail::d2::operator-<tbb::detail::d2::concurrent_hash_map<int, int, tbb::detail::d1::tbb_hash_compare<int>, tbb::detail::d1::tbb_allocator<std::pair<int const, int> > >, std::pair<int const, int>, std::pair<int const, int> >(tbb::detail::d2::hash_map_iterator<tbb::detail::d2::concurrent_hash_map<int, int, tbb::detail::d1::tbb_hash_compare<int>, tbb::detail::d1::tbb_allocator<std::pair<int const, int> > >, std::pair<int const, int> > const&, tbb::detail::d2::hash_map_iterator<tbb::detail::d2::concurrent_hash_map<int, int, tbb::detail::d1::tbb_hash_compare<int>, tbb::detail::d1::tbb_allocator<std::pair<int const, int> > >, std::pair<int const, int> > const&)'
collect2: error: ld returned 1 exit status

Expected Behavior

Linking succeeds

Steps To Reproduce

Try to compile and link following code:

#include <tbb/concurrent_hash_map.h>

int main()
{
	tbb::concurrent_hash_map<int, int> hashMap;
	return hashMap.end() - hashMap.begin();
}

[dnmokhov]

Thank you for your question, @IvanSavenko.

The types concurrent_hash_map::iterator and concurrent_hash_map::const_iterator meet the requirements of ForwardIterator from the [forward.iterators] ISO C++ Standard section (https://oneapi-spec.uxlfoundation.org/specifications/oneapi/latest/elements/onetbb/source/containers/concurrent_hash_map_cls/iterators).

ForwardIterator cannot be used with arithmetic operators. Consider using std::distance instead:

-	return return hashMap.end() - hashMap.begin();
+	return std::distance(hashMap.begin(), hashMap.end());

[IvanSavenko]

But it can (according to iterator definition):

oneTBB/include/oneapi/tbb/concurrent_hash_map.h

Line 431 in 52a7b37

friend ptrdiff_t operator-( const hash_map_iterator<C,T>& i, const hash_map_iterator<C,U>& j );

As result, example code compiles, but fails to link since this operator is declared, but not defined.

I presume correct solution would be to remove definition of operator- from hash_map_iterator

[IvanSavenko]

Another example of code that also fails to link (and a bit closer to what we actually encountered)

#include <tbb/concurrent_hash_map.h>

int main()
{
	tbb::concurrent_hash_map<int, int> hashMap;
	return std::ranges::distance(hashMap.begin(), hashMap.end());
}

With gcc-13 and gcc-15 this code fails to link in C++20 mode. Note that only std::ranges::distance has this behavior - std::distance compiles & links without issues.

From what I see, std::ranges::distance actually testes for operator- presence via sized_sentinel_for. And hash_map_iterator currently fulfills this requirement

[dnmokhov]

I presume correct solution would be to remove definition of operator- from hash_map_iterator

Removed in master, so targeted for the next release. Thanks again for reporting this, @IvanSavenko!