asyncio

What asyncio is ?

• asyncio is Python’s asynchronous I/O framework.

• It allows you to write code that looks sequential but actually does many tasks concurrently without using multiple threads or processes.

• It’s single-threaded and usually single-process, but it can manage thousands of I/O-bound tasks efficiently.

• Think of it as a cooperative multitasking system inside one thread.

How it works

• You write coroutines with async def.

• You use await to pause a coroutine when it’s waiting for I/O (network, disk, etc.), letting other coroutines run.

• The event loop schedules tasks efficiently.

You must run in normal script, not in Jupyter Notebook

import asyncio

async def say_after(delay, msg):
    await asyncio.sleep(delay)  # non-blocking sleep
    print(msg)

async def main():
    # run two tasks concurrently
    await asyncio.gather(
        say_after(2, "Hello"),
        say_after(1, "World")
    )

asyncio.run(main())

How asyncio compares to threads and processes

Feature	Threading	Multiprocessing	asyncio
Parallel CPU usage	No (GIL)	Yes	No (single thread)
Concurrency type	OS-level (preemptive)	OS-level (parallel)	Cooperative (event-driven)
Memory overhead	Low	High	Very low
I/O-bound tasks	Good	Works, heavier	Excellent (lightweight)
CPU-bound tasks	Inefficient	Excellent	Not suitable
Complexity	Moderate (locks)	Higher	Moderate (async/await syntax)

Purpose / When to use asyncio

• Handle many I/O tasks efficiently without threads or processes. Examples: web servers, network clients, chat apps.

• Avoid thread overhead and locking issues. Threads require careful synchronization; asyncio uses single-threaded cooperative multitasking.

• Scale thousands of concurrent tasks cheaply. Example: a server handling 10,000 client connections can use a single process with asyncio instead of 10,000 threads.

---

import asyncio

async def say_after(delay, msg):
    await asyncio.sleep(delay)  # non-blocking sleep
    print(msg)

async def main():
    # run two tasks concurrently
    await asyncio.gather(
        say_after(2, "Hello"),
        say_after(1, "World")
    )

    return 111

def nguoidingoaipho():
    pass

v = main()

HHHHHH: <_UnixSelectorEventLoop running=True closed=False debug=False>
HHHHHH: <_UnixSelectorEventLoop running=True closed=False debug=False>
HHHHHH: <_UnixSelectorEventLoop running=True closed=False debug=False>
HHHHHH: <_UnixSelectorEventLoop running=True closed=False debug=False>
HHHHHH: <_UnixSelectorEventLoop running=True closed=False debug=False>
HHHHHH: <_UnixSelectorEventLoop running=True closed=False debug=False>

dir(v)

import inspect

inspect.getcoroutinestate(v)

from asyncio.events import _get_running_loop

_get_running_loop()

import asyncio
asyncio.events._running_loop.loop_pid