What are semaphores in programming and can you give examples?

What are semaphores in programming and can you give examples?

Semaphores are synchronization tools used to control access to shared resources in concurrent programming. For example, in a multi-threaded application, a semaphore can limit the number of threads that access a particular resource at the same time.

Can you explain how a binary semaphore works?

A binary semaphore is a type of semaphore that can only take two values: 0 and 1. It is used to implement mutual exclusion, allowing only one thread to access a resource at a time. When a thread acquires the semaphore, it sets it to 0, and when it releases it, it sets it back to 1.

What is the difference between a binary semaphore and a counting semaphore?

The main difference is that a binary semaphore can only be 0 or 1, while a counting semaphore can take any non-negative integer value. Counting semaphores are used to control access to a resource pool with multiple identical resources.

Can you provide a code example of using a semaphore in Python?

Sure! Here's a simple example using Python's threading module:

import threading

semaphore = threading.Semaphore(2)  # Allow 2 threads to access the resource

def access_resource():
    with semaphore:
        print('Accessing resource...')
        # Simulate resource access
        time.sleep(1)

threads = [threading.Thread(target=access_resource) for _ in range(5)]
for thread in threads:
    thread.start()
for thread in threads:
    thread.join()