Condition variables
Condition variables are another synchronization primitive provided by the C++ Standard Library. They allow multiple threads to communicate with each other. They also allow for several threads to wait for a notification from another thread. Condition variables are always associated with a mutex.
In the following example, a thread must wait for a counter to be equal to a certain value:
#include <chrono>
#include <condition_variable>
#include <iostream>
#include <mutex>
#include <thread>
#include <vector>
int counter = 0;
int main() {
    using namespace std::chrono_literals;
    std::mutex mtx;
    std::mutex cout_mtx;
    std::condition_variable cv;
    auto increment_counter = [&] {
        for (int i = 0; i < 20; ++i) {
         &...
