How do multithreading, multiprocessing, and asynchronous execution differ? When should each be used?

Multithreading is the execution of multiple threads within a single process, which can run in parallel, sharing memory. It is useful for tasks with a large number of input/output operations or when parallelizing computations, but there are limitations due to GIL in Python.

Multiprocessing involves running multiple processes, each with its own memory. It allows overcoming GIL limitations and efficiently utilizing multiple CPU cores. Suitable for CPU-intensive tasks.

Asynchronous programming is a model where tasks do not block execution but work through events and callbacks (or async/await). It is well-suited for a large number of input/output operations, such as network requests.

When to use what:

• Multithreading — for tasks with blocking input/output, where it is necessary to process multiple threads in parallel.
• Multiprocessing — for CPU-intensive tasks requiring parallel processing.
• Asynchronous — for scalable network applications with many input/output operations and the need to efficiently utilize resources without creating many threads.

Example of asynchronous code in Python:

import asyncio

async def fetch_data():
    await asyncio.sleep(1)  # simulate input/output
    return 'data'

async def main():
    results = await asyncio.gather(fetch_data(), fetch_data())
    print(results)

asyncio.run(main())