How do I use semaphores in threads?

How do I use semaphores in threads?

Semaphores are synchronization tools that help manage 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 using the threading module:

import threading
import time

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

def worker(num):
    print(f'Worker {num} is trying to acquire the semaphore.')
    with semaphore:
        print(f'Worker {num} has acquired the semaphore.')
        time.sleep(2)  # Simulate work
    print(f'Worker {num} has released the semaphore.')

# Create multiple threads
threads = [threading.Thread(target=worker, 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()

This code creates a semaphore that allows up to 2 threads to access the critical section at the same time.

What happens if more than 2 threads try to acquire the semaphore?

If more than 2 threads try to acquire the semaphore, the additional threads will be blocked until one of the currently running threads releases the semaphore. This ensures that only 2 threads can access the critical section simultaneously.