What are some examples of semaphores in code?

Can you explain what semaphores are in programming?

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

Can you give me some examples of semaphores in code?

Absolutely! Here's a simple example in Python using the threading module:

import threading

# Create a semaphore with a limit of 2
semaphore = threading.Semaphore(2)

def access_resource(thread_id):
    print(f'Thread {thread_id} is trying to access the resource.')
    semaphore.acquire()
    print(f'Thread {thread_id} has accessed the resource.')
    # Simulate resource usage
    semaphore.release()
    print(f'Thread {thread_id} has released the resource.')

# Create multiple threads
threads = [threading.Thread(target=access_resource, args=(i,)) for i in range(5)]

# Start the threads
for thread in threads:
    thread.start()

# Wait for all threads to complete
for thread in threads:
    thread.join()

What happens if more threads try to access the resource than the semaphore allows?

If more threads try to access the resource than the semaphore allows, they will be blocked until a slot becomes available. This ensures that only a limited number of threads can access the resource simultaneously.