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Thread hardware_concurrency() function in C++

  • Last Updated : 30 Oct, 2018

Thread::hardware_concurrency is an in-built function in C++ std::thread. It is an observer function which means it observes a state and then returns the corresponding output. This function returns the number of concurrent threads supported by the available hardware implementation. This value might not always be accurate.



Parameters: This function does not accept any parameters.

Return Value: It returns a non-negative integer denoting the number of concurrent threads supported by the system. If the value is either not computable or not well defined it returns 0.

Below program demonstrate the use of std::thread::joinable()

Note: On the online IDE this program will show error. To compile this, use the flag “-pthread” on g++ compilers compilation with the help of command “g++ –std=c++14 -pthread file.cpp”.

// C++ program to demonstrate the use of
// std::thread::hardware_concurrency()
#include <chrono>
#include <iostream>
#include <thread>
using namespace std;
int main()
    unsigned int con_threads;
    // calculating number of concurrent threads
    // supported in the hardware implementation
    con_threads = thread::hardware_concurrency();
    cout << "Number of concurrent threads supported are: "
         << con_threads << endl;
    return 0;

Possible Output

Number of concurrent threads supported are: 4
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