This std::thread examples demonstrates how to use std::mutexes to share std::cout nicely, as in the previous example, std::thread example 1: two counting threads, the output to std::cout was messy.

Download the Qt Creator project 'CppThreadExample2' (zip)


#include <iostream>

#include <thread>



void DoCountDown(const int id)

{

  //static mutex, because each thread its must use the same mutex

  static std::mutex mutex;



  for (int i=0; i!=10; ++i)

  {

    ///Let this thread sleep, to give the other thread a chance

    std::this_thread::sleep_for(std::chrono::milliseconds(1));



    ///Acquire access to std::cout

    std::lock_guard<std::mutex> lock(mutex);



    ///Write to std::cout

    std::cout << "#" << id << ": " << (10-i) << '\n';

  }

}



int main()

{

  std::thread t1(DoCountDown,1);

  std::thread t2(DoCountDown,2);

  t1.join();

  t2.join();

}

Screen output:


#2: 10

#1: 10

#2: 9

#1: 9

#2: 8

#1: 8

#2: 7

#1: 7

#2: 6

#1: 6

#2: 5

#1: 5

#2: 4

#1: 4

#2: 3

#1: 3

#2: 2

#1: 2

#2: 1

#1: 1

This example is checked for errors in helgrind example 2: two counting threads using std::mutex, where helgrind is shown to detect no errors.

References

Bjarne Stroustrup's C++0x page

Go back to Richel Bilderbeek's C++ page.

Go back to Richel Bilderbeek's homepage.

(C++) std::thread example 2: two counting threads using std::mutex

References