What are semaphores in Python and how do they work?

What are semaphores in Python and how do they work?

Semaphores are synchronization primitives that control access to a shared resource in concurrent programming. They maintain a count that represents the number of available resources.

Can you give me an example of how to implement a semaphore in Python?

Sure! You can use the threading module. Here's a simple example:

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

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

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

What happens if a thread tries to acquire a semaphore that is already at its limit?

If a thread tries to acquire a semaphore that is at its limit, it will block and wait until a resource becomes available (i.e., another thread releases the semaphore). This ensures that only a limited number of threads can access the resource at the same time.