由浅入深介绍python asyncio的各种用法与代码示例_Python

下面是一份“由浅入深”的 asyncio 实战手册。先解释核心概念，再给出可直接运行的、循序渐进的示例代码。全部示例都只依赖标准库（除少数标注处），适配 python 3.10+（如使用 taskgroup、asyncio.timeout() 的段落需要 3.11+）。

1. 基础概念速览

async def：定义协程函数（coroutine function）。
await：在协程中等待另一个可等待对象（协程、asyncio.task、asyncio.future 等）。
事件循环（event loop）：调度协程、i/o 事件的核心；用 asyncio.run(main()) 启动。
并发 ≠ 并行：asyncio 是单线程协作式并发，靠 i/o 等待时让出控制权。
任务（task）：把协程“提交给”事件循环让其并发执行：asyncio.create_task(coro())。

2. 最小可运行示例：async/await+asyncio.run

# demo_basic.py
import asyncio

async def io_job(name, delay):
    print(f"[{name}] start")
    await asyncio.sleep(delay)  # 模拟i/o等待
    print(f"[{name}] done after {delay}s")
    return name, delay

async def main():
    r1 = await io_job("a", 1)
    r2 = await io_job("b", 2)  # 串行等待，总耗时约3秒
    print("results:", r1, r2)

if __name__ == "__main__":
    asyncio.run(main())

3. 并发执行：create_task、gather、as_completed

# demo_concurrency.py
import asyncio, random

async def fetch(i):
    d = random.uniform(0.5, 2.0)
    await asyncio.sleep(d)
    return f"task-{i}", round(d, 2)

async def main():
    # 3.1 create_task + await
    t1 = asyncio.create_task(fetch(1))
    t2 = asyncio.create_task(fetch(2))
    r1 = await t1
    r2 = await t2
    print("create_task results:", r1, r2)

    # 3.2 gather（顺序返回结果；遇异常默认会立刻抛出）
    results = await asyncio.gather(*(fetch(i) for i in range(3, 8)))
    print("gather results:", results)

    # 3.3 as_completed（谁先完成先拿谁）
    tasks = [asyncio.create_task(fetch(i)) for i in range(8, 13)]
    for fut in asyncio.as_completed(tasks):
        print("as_completed:", await fut)

if __name__ == "__main__":
    asyncio.run(main())

4. 超时控制与取消：wait_for、asyncio.timeout、task.cancel

# demo_timeout_cancel.py
import asyncio

async def slow():
    try:
        await asyncio.sleep(5)
        return "ok"
    except asyncio.cancellederror:
        print("slow() got cancelled!")
        raise

async def main():
    # 4.1 wait_for（3.8+）
    try:
        res = await asyncio.wait_for(slow(), timeout=2)
        print("result:", res)
    except asyncio.timeouterror:
        print("wait_for timeout!")

    # 4.2 asyncio.timeout 上下文（3.11+）
    try:
        async with asyncio.timeout(2):  # 注：需 python 3.11+
            await slow()
    except timeouterror:
        print("context timeout!")

    # 4.3 手动取消
    t = asyncio.create_task(slow())
    await asyncio.sleep(1)
    t.cancel()
    try:
        await t
    except asyncio.cancellederror:
        print("task cancelled confirmed")

if __name__ == "__main__":
    asyncio.run(main())

小贴士：被取消的任务应正确处理 cancellederror，并在需要时做清理（finally）。

5. 限流与同步原语：semaphore、lock、event、condition

# demo_sync_primitives.py
import asyncio, random

sem = asyncio.semaphore(3)  # 同时最多3个并发
lock = asyncio.lock()
evt = asyncio.event()

async def worker(i):
    async with sem:  # 限制并发
        await asyncio.sleep(random.uniform(0.2, 1.0))
        async with lock:  # 保护共享输出（示意）
            print(f"worker {i} done")

async def notifier():
    await asyncio.sleep(1)
    evt.set()  # 广播事件

async def waiter():
    print("waiting for event...")
    await evt.wait()
    print("event received!")

async def main():
    tasks = [asyncio.create_task(worker(i)) for i in range(10)]
    tasks += [asyncio.create_task(notifier()), asyncio.create_task(waiter())]
    await asyncio.gather(*tasks)

if __name__ == "__main__":
    asyncio.run(main())

condition 适合更复杂的“等待某条件成立”的场景，用法与 threading.condition 类似（只是换成 async with / await）。

6. 生产者-消费者：asyncio.queue

# demo_queue.py
import asyncio, random

async def producer(q: asyncio.queue):
    for i in range(10):
        await asyncio.sleep(random.uniform(0.1, 0.4))
        await q.put((i, f"data-{i}"))
        print(f"produced {i}")
    await q.put(none)  # 结束哨兵

async def consumer(q: asyncio.queue):
    while true:
        item = await q.get()
        if item is none:
            q.task_done()
            break
        i, data = item
        await asyncio.sleep(0.3)
        print(f"consumed {i} -> {data}")
        q.task_done()

async def main():
    q = asyncio.queue(maxsize=5)
    prod = asyncio.create_task(producer(q))
    cons = asyncio.create_task(consumer(q))
    await asyncio.gather(prod)
    await q.join()        # 等全部消费完成
    await cons            # 等消费者退出

if __name__ == "__main__":
    asyncio.run(main())

7. 任务编组（python 3.11+）：asyncio.taskgroup

# demo_taskgroup.py
import asyncio, random

async def job(n):
    await asyncio.sleep(random.uniform(0.2, 1.0))
    if n == 3:
        raise runtimeerror("boom at 3")
    return n

async def main():
    try:
        async with asyncio.taskgroup() as tg:
            tasks = [tg.create_task(job(i)) for i in range(5)]
            # 出错会自动取消其余任务并向外传播异常
    except* runtimeerror as eg:  # pep 654（exceptiongroup）
        print("caught:", eg)

if __name__ == "__main__":
    asyncio.run(main())

对比 gather：taskgroup 在结构化并发上更可靠，失败会自动收拢与传播。

8. 与线程/同步代码协作：to_thread、run_in_executor

# demo_thread_bridge.py
import asyncio, time, concurrent.futures

def blocking_io(n):
    time.sleep(n)
    return f"blocking {n}s"

async def main():
    # 8.1 python 3.9+ 推荐：to_thread
    r1 = await asyncio.to_thread(blocking_io, 1)
    print("to_thread:", r1)

    # 8.2 传统：run_in_executor
    loop = asyncio.get_running_loop()
    with concurrent.futures.threadpoolexecutor(max_workers=3) as pool:
        futs = [loop.run_in_executor(pool, blocking_io, i) for i in (1, 2, 1)]
        for r in await asyncio.gather(*futs):
            print("executor:", r)

if __name__ == "__main__":
    asyncio.run(main())

原则：cpu 密集就放线程/进程池；i/o 密集用 await 原生异步接口。

9. tcp/udp 网络编程（内置 streams / protocols）

9.1 tcp echo（server & client，基于 streams）

# demo_tcp_echo.py
import asyncio

async def handle_echo(reader: asyncio.streamreader, writer: asyncio.streamwriter):
    addr = writer.get_extra_info('peername')
    print(f"client connected: {addr}")
    try:
        while data := await reader.readline():
            msg = data.decode().rstrip()
            print(f"recv: {msg}")
            writer.write((msg + "\n").encode())
            await writer.drain()
    except asyncio.cancellederror:
        raise
    finally:
        writer.close()
        await writer.wait_closed()
        print("client closed", addr)

async def run_server():
    server = await asyncio.start_server(handle_echo, "127.0.0.1", 8888)
    addrs = ", ".join(str(sock.getsockname()) for sock in server.sockets)
    print(f"serving on {addrs}")
    async with server:
        await server.serve_forever()

async def run_client():
    reader, writer = await asyncio.open_connection("127.0.0.1", 8888)
    for i in range(3):
        writer.write(f"hello {i}\n".encode())
        await writer.drain()
        echo = await reader.readline()
        print("echo:", echo.decode().rstrip())
    writer.close()
    await writer.wait_closed()

async def main():
    server_task = asyncio.create_task(run_server())
    await asyncio.sleep(0.2)
    await run_client()
    server_task.cancel()
    with contextlib.suppress(asyncio.cancellederror):
        await server_task

if __name__ == "__main__":
    import contextlib
    asyncio.run(main())

9.2 udp（datagram）

# demo_udp.py
import asyncio

class echoserver(asyncio.datagramprotocol):
    def datagram_received(self, data, addr):
        print("server recv:", data, "from", addr)
        self.transport.sendto(data, addr)

async def main():
    loop = asyncio.get_running_loop()
    transport, _ = await loop.create_datagram_endpoint(
        lambda: echoserver(), local_addr=("127.0.0.1", 9999)
    )
    # client
    on_resp = loop.create_future()
    class client(asyncio.datagramprotocol):
        def datagram_received(self, data, addr):
            print("client recv:", data)
            on_resp.set_result(none)
    ctransport, _ = await loop.create_datagram_endpoint(
        lambda: client(), remote_addr=("127.0.0.1", 9999)
    )
    ctransport.sendto(b"hello-udp")
    await on_resp
    transport.close()
    ctransport.close()

if __name__ == "__main__":
    asyncio.run(main())

10. 子进程（异步等待）：asyncio.create_subprocess_exec

# demo_subprocess.py
import asyncio, sys

async def main():
    # 跨平台示例：调用 python -c 'print("hi")'
    proc = await asyncio.create_subprocess_exec(
        sys.executable, "-c", 'print("hi from child")',
        stdout=asyncio.subprocess.pipe, stderr=asyncio.subprocess.pipe
    )
    out, err = await proc.communicate()
    print("stdout:", out.decode().strip(), "| code:", proc.returncode)

if __name__ == "__main__":
    asyncio.run(main())

11. 异步上下文管理器与迭代器：async with、async for

# demo_async_with_for.py
import asyncio
from contextlib import asynccontextmanager

@asynccontextmanager
async def open_resource():
    print("acquire resource")
    await asyncio.sleep(0.2)
    try:
        yield "resource"
    finally:
        await asyncio.sleep(0.2)
        print("release resource")

class asynccounter:
    def __init__(self, n): self.n=n; self.i=0
    def __aiter__(self): return self
    async def __anext__(self):
        if self.i >= self.n:
            raise stopasynciteration
        await asyncio.sleep(0.1)
        self.i += 1
        return self.i

async def main():
    async with open_resource() as r:
        print("using:", r)
    async for x in asynccounter(5):
        print("got:", x)

if __name__ == "__main__":
    asyncio.run(main())

12. 超实用模式集

12.1 背压与批处理

# demo_backpressure.py
import asyncio, random

async def producer(q):
    for i in range(30):
        await q.put(i)             # maxsize 限制可形成背压
        await asyncio.sleep(0.05)
    await q.put(none)

async def consumer(q):
    batch = []
    while true:
        item = await q.get()
        if item is none:
            if batch:
                print("flush batch:", batch)
            q.task_done()
            break
        batch.append(item)
        if len(batch) >= 8:
            # 模拟批量处理
            await asyncio.sleep(random.uniform(0.1, 0.3))
            print("process batch:", batch)
            batch.clear()
        q.task_done()

async def main():
    q = asyncio.queue(maxsize=10)
    await asyncio.gather(producer(q), consumer(q))
    await q.join()

if __name__ == "__main__":
    asyncio.run(main())

12.2 幂等重试 + 指数退避

# demo_retry.py
import asyncio, random

async def fragile_call():
    await asyncio.sleep(0.1)
    if random.random() < 0.7:
        raise runtimeerror("transient")
    return "ok"

async def retry(coro_func, attempts=5, base=0.2):
    for n in range(attempts):
        try:
            return await coro_func()
        except exception as e:
            if n == attempts - 1:
                raise
            await asyncio.sleep(base * (2 ** n))  # 退避
    raise runtimeerror("unreachable")

async def main():
    try:
        r = await retry(fragile_call)
        print("result:", r)
    except exception as e:
        print("failed:", e)

if __name__ == "__main__":
    asyncio.run(main())

13. 常见坑与最佳实践

入口统一用 asyncio.run(main())，不要混用早期 api（如手动获取 loop、run_until_complete），除非有特殊需求。

避免阻塞调用（如 time.sleep()、重 cpu 任务）直接出现在协程里；改用 await asyncio.sleep() 或 asyncio.to_thread()/进程池。

正确处理取消：在 try/except/finally 中传播 cancellederror，避免吞掉取消导致任务“僵尸化”。

使用限流：对外部服务/磁盘/网络做 semaphore、队列背压，保护系统。

结构化并发：优先考虑 taskgroup（3.11+）来让“任务生命周期”明确，异常聚合安全。

日志与超时：给关键 i/o 加 timeout，并使用 asyncio.create_task() 后保存句柄，便于监控和取消。

14. 进阶延伸（可选）

文件异步：标准库没有真正异步文件 i/o；可选三方库 aiofiles（仅示意）：

# pip install aiofiles
import aiofiles, asyncio
async def read_file(p):
    async with aiofiles.open(p, "r", encoding="utf-8") as f:
        return await f.read()

http 客户端/服务端：aiohttp、httpx[http2] 等第三方库更贴近真实网络场景。

与 gui/qt 的集成：可通过 qasync 把 qt 事件循环与 asyncio 融合（适合你在 qml/pyside6 下需要异步网络/io 的情况）。

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由浅入深介绍python asyncio的各种用法与代码示例

2025年11月05日 • Python •我要评论