communicate_with_condition_variable.cpp

#include <iostream>
#include <future>
#include <thread>
#include <string>
#include <condition_variable>
#include <vector>

std::mutex m1;
std::mutex cout_mutex;
std::condition_variable wait_till_run;
bool go = false;

void hundredMeterRace(const std::string& name)
{
    {
        std::unique_lock<std::mutex> lg(m1);

        wait_till_run.wait(lg, []()
        {
            return go;
        });
    }
    std::lock_guard<std::mutex> cm(cout_mutex);
    std::cout << name << " starts running\n";
}

int main()
{
    std::vector<std::thread> vcTh;
    std::vector<std::string> names = { "Nash", "Sam", "Bolt" };
    
    for (const auto& name : names)
    {
        vcTh.emplace_back(hundredMeterRace, std::cref(name));
    }
    {
        std::lock_guard<std::mutex> cm(cout_mutex);
        std::cout << "Ready .... Set ... Go\n";
    }
    go = true;
    wait_till_run.notify_all();
    for (auto& th : vcTh)
    {
        th.join();
    }
}
/*Output
Ready .... Set ... Go
Sam starts running
Nash starts running
Bolt starts running
*/