What exactly does hardware_concurrency() return?

[ClobberXD]

It returns an unsigned int. But what exactly is that int supposed to be? If a hyper-threaded 4-core i7 CPU has 8 threads (duh...), will the function return 4 or 8?

[zMeul]

Return value

number of concurrent threads supported

 

it should return 8, test it

[Unimportant]

System and implementation specific - which means it can return anything.

A system can support multiple threads per processing unit, or access to (some) processing units can be denied to your program by the OS so the result need not match the amount of cores in your CPU.

[ClobberXD]

2 hours ago, zMeul said:

Return value

number of concurrent threads supported

 

it should return 8, test it

I can't test it, as I don't have a hyper-threaded CPU... But thanks!

[zMeul]

2 hours ago, Anand_Geforce said:

I can't test it, as I don't have a hyper-threaded CPU... But thanks!

you just need someone with a puny i3 laptop - they're hyper-threaded 

[trag1c]

The results as expected with an i7-5820k. However std::thread::hardware_concurrency is platform specific and implementation specific meaning that the results can be different across OS's and hardware.

int  main()
{
	std::thread t;

	int numThreads = t.hardware_concurrency();

	std::cout << "Number of Threads: " << numThreads << std::endl;

	std::cin.get();
	return 0;	
}

 

[ClobberXD]

6 hours ago, trag1c said:

The results as expected with an i7-5820k. However std::thread::hardware_concurrency is platform specific and implementation specific meaning that the results can be different across OS's and hardware.

int  main()
{
	std::thread t;

	int numThreads = t.hardware_concurrency();

	std::cout << "Number of Threads: " << numThreads << std::endl;

	std::cin.get();
	return 0;	
}

 

Thanks a ton - that was really helpful!

[trag1c]

2 minutes ago, Anand_Geforce said:

Thanks a ton - that was really helpful!

Happy to help.