What is a semaphore in C++?

What is a semaphore in C++?

A semaphore in C++ is a synchronization primitive that controls access to a common resource by multiple threads.

How does a semaphore differ from a mutex?

A semaphore allows multiple threads to access a resource up to a limit, while a mutex allows only one thread at a time.

Can you give me an example of using a semaphore?

Sure! Here's a simple example:

#include <semaphore.h>
#include <thread>
#include <iostream>

sem_t semaphore;

void accessResource(int id) {
    sem_wait(&semaphore);
    std::cout << "Thread " << id << " is accessing the resource." << std::endl;
    // Simulate resource access
    std::this_thread::sleep_for(std::chrono::seconds(1));
    std::cout << "Thread " << id << " is done accessing the resource." << std::endl;
    sem_post(&semaphore);
}

int main() {
    sem_init(&semaphore, 0, 2); // Allow 2 threads to access the resource
    std::thread t1(accessResource, 1);
    std::thread t2(accessResource, 2);
    std::thread t3(accessResource, 3);
    t1.join(); t2.join(); t3.join();
    sem_destroy(&semaphore);
    return 0;
}

What happens if a thread tries to access the resource when it's full?

If a thread tries to access the resource when the semaphore count is zero, it will block until another thread releases the semaphore.