main.cc

#include <mutex>
#include <condition_variable>
#include <thread>
#include <chrono>
#include <string>
#include <iostream>

std::atomic<bool> sigg;
std::string s = "na";
std::mutex m;
std::condition_variable v;

bool pred() {return sigg;}

void a() {
    std::unique_lock<std::mutex> lock(m);
    printf("waiting for cv...\n");
    v.wait(lock, pred);
    std::cout << "Finished waiting: " << s << "\n";
}

void b() {
    std::unique_lock<std::mutex> lock(m);
    sigg = true;
    printf("doing something...\n");
    std::this_thread::sleep_for(std::chrono::seconds(3));
    s = "hello world";
    printf("notifying\n");
    v.notify_one();
}

int main() {
    std::thread t1(a), t2(b);
    t1.join();
    t2.join();

    return 0;
}