What are semaphores in C?

Can you explain what semaphores are in C?

Sure! Semaphores are synchronization tools used to control access to a common resource in concurrent programming.

How do they work in a multi-threaded environment?

In a multi-threaded environment, semaphores help prevent race conditions by allowing only a certain number of threads to access a resource at the same time.

Can you give me an example of using semaphores in C?

Certainly! Here's a simple example using POSIX semaphores:

#include <semaphore.h>
#include <pthread.h>
#include <stdio.h>

sem_t semaphore;

void* thread_function(void* arg) {
    sem_wait(&semaphore);
    // Critical section
    printf("Thread %d is in the critical section.\n", *(int*)arg);
    sem_post(&semaphore);
    return NULL;
}

int main() {
    pthread_t threads[5];
    sem_init(&semaphore, 0, 1);
    int thread_ids[5];
    for (int i = 0; i < 5; i++) {
        thread_ids[i] = i;
        pthread_create(&threads[i], NULL, thread_function, &thread_ids[i]);
    }
    for (int i = 0; i < 5; i++) {
        pthread_join(threads[i], NULL);
    }
    sem_destroy(&semaphore);
    return 0;
}

What are the differences between binary and counting semaphores?

Binary semaphores can only take values 0 or 1, while counting semaphores can take any non-negative integer value, allowing more flexible resource management.