How do I use semaphores in threading?

How do I use semaphores in threading?

Semaphores are synchronization primitives that help control access to shared resources in concurrent programming. Would you like a code example?

Yes, please provide a code example in Python.

Sure! Here's a simple 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.')
    semaphore.acquire()
    print(f'Thread {thread_id} has accessed the resource.')
    time.sleep(2)  # Simulate resource usage
    print(f'Thread {thread_id} is releasing the resource.')
    semaphore.release()

threads = []
for i in range(5):
    t = threading.Thread(target=access_resource, args=(i,))
    threads.append(t)
    t.start()

for t in threads:
    t.join()

This code creates a semaphore that allows up to 2 threads to access the resource simultaneously.

What happens if more than 2 threads try to access the resource?

If more than 2 threads try to access the resource, they will be blocked until one of the threads currently holding the semaphore releases it. This ensures that only 2 threads can access the resource at the same time.