What are semaphores in Python and how do I use them?

What are semaphores in Python and how do I use them?

Semaphores are synchronization primitives that control access to a shared resource in concurrent programming. In Python, you can use the threading module to implement semaphores.

Can you show me a simple example of using a semaphore?

Sure! Here's a basic example:

import threading
import time

# 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.')
    with semaphore:
        print(f'Thread {thread_id} has accessed the resource.')
        time.sleep(2)  # Simulate resource usage
    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.