The leftright from mmcshane

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Multiple function definition, link error.

Definition of functions atomic_reader_registry::depart, atomic_reader_registry::arrive, atomic_reader_registry::empty misses inline keyword.
Non template class function declared in header must be inline.

Interesting behaviour

Hi i have decided to test leftright implementation of yours.

write thread updates leftright protected Big struct.
read thread reads updated values and checks if read struct is half updated.

I have run this test on x86_64 cpu and i read half updated values.

I dont think this is the expected behaviour but want to ask anyways.
Is this expected behaviour?

Sample output
failed 23096 23097 23097 23097
failed 72977 72977 72977 72979
failed 109959 109959 109959 109960

Here is the test code.

struct Big
{
private:
	alignas(std::hardware_destructive_interference_size) int a1{};
	alignas(std::hardware_destructive_interference_size) int a2{};
	alignas(std::hardware_destructive_interference_size) int a3{};
	alignas(std::hardware_destructive_interference_size) int a4{};

public:
	void add1()
	{
		a1 += 1;
		a2 += 1;
		a3 += 1;
		a4 += 1;
	}

	void print() const
	{
		std::cout << a1 << ' ' << a2 << ' ' << a3 << ' ' << a4 << std::endl;
	}

	void check() const
	{
		if ((a1 == a2) && (a1 == a3) && (a1 == a4))
		{
		}
		else
		{
			std::cout << "failed ";
			this->print();
		}
	}
};

template <typename T>
struct leftright_wrap
{
	mpm::leftright<T> lr;

	auto read() const noexcept
	{
		return lr.observe([](const auto &val) noexcept
						  { return val; });
	}

	auto write(const T &t) noexcept
	{
		lr.modify([&t](auto &val) noexcept
				  { val = t; });
	}
};

int main()
{

	leftright_wrap<Big> lr;

	std::thread read_([&lr]
					  {
						  while (true)
						  {
							  auto a = lr.read();
							  a.check(); //! should not see half updated value
						  }
					  }

	);

	std::thread write_([&lr]
					   {
						   Big big{};
						   while (true)
						   {
							   big.add1();
							   lr.write(big);
						   }
					   }

	);

	read_.join();
	write_.join();
}

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