What are semaphores in C++?

What are semaphores in C++?

Semaphores are synchronization primitives used to control access to a common resource in concurrent programming.

How do I use semaphores in the C++ standard library?

You can use the <semaphore> header in C++20, which provides the std::counting_semaphore and std::binary_semaphore classes.

Can you give me an example of using a counting semaphore?

Sure! Here's a simple example:

#include <iostream>
#include <semaphore>
#include <thread>

std::counting_semaphore<1> sem;

void accessResource(int id) {
    sem.acquire(); // Wait
    std::cout << "Thread " << id << " is accessing the resource.\n";
    std::this_thread::sleep_for(std::chrono::seconds(1));
    std::cout << "Thread " << id << " is done.\n";
    sem.release(); // Signal
}

int main() {
    std::thread t1(accessResource, 1);
    std::thread t2(accessResource, 2);
    t1.join();
    t2.join();
    return 0;
}

What is the difference between counting and binary semaphores?

Counting semaphores can have a value greater than one, allowing multiple threads to access a resource, while binary semaphores can only be 0 or 1, allowing only one thread at a time.