```Python
with open("file.txt") as file:
    file.read()
```

Python 的最近几个版本也有了一个**异步上下文管理器**，你可以通过 `async with` 来使用：

```Python
async with lifespan(app):
    await do_stuff()
```

你可以像上面一样创建了一个上下文管理器或者异步上下文管理器，它的作用是在进入 `with` 块时，执行 `yield` 之前的代码，并且在离开 `with` 块时，执行 `yield` 后面的代码。

但在我们上面的例子里，我们并不是直接使用，而是传递给 FastAPI 来供其使用。

./mc cp README.md myminio1/foobucket/dir/file

versionId="$(./mc ls --json --versions myminio1/foobucket/dir/ | jq -r .versionId)"

kill ${pid2} && wait ${pid2} || true

aws s3api --endpoint-url http://localhost:9001 delete-object --bucket foobucket --key dir/file --version-id "$versionId"

out="$(./mc ls myminio1/foobucket/dir/)"
if [ "$out" != "" ]; then

    return {"item_id": item_id, "q": q}
```

<details markdown="1">
<summary>Або використайте <code>async def</code>...</summary>

Якщо ваш код використовує `async` / `await`, скористайтеся `async def`:

```Python hl_lines="9  14"
from typing import Union

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
async def read_root():

        try {
            rateLimiter.checkAttempt(username, ip);
            fail("Should be locked out");
        } catch (SmbException e) {
            // Expected
        }

        // Wait for lockout to expire
        Thread.sleep(2100); // Lockout is 2 seconds in test setup

        // Should be allowed again
        assertTrue(rateLimiter.checkAttempt(username, ip), "Should be allowed after lockout expiry");

		return nil, err
	}

	return obj, nil
}

// TransferError will catch network errors during transfer.
// When TransferError() is called Close() will also
// be called, so we do not need to Wait() here.
func (w *writerAt) TransferError(err error) {
	_ = w.w.CloseWithError(err)
	_ = w.r.CloseWithError(err)
	w.err = err
}

func (w *writerAt) Close() (err error) {
	switch {

**FastAPI** 会创建一个 `BackgroundTasks` 类型的对象并作为该参数传入。

## 创建一个任务函数

创建要作为后台任务运行的函数。

它只是一个可以接收参数的标准函数。

它可以是 `async def` 或普通的 `def` 函数，**FastAPI** 知道如何正确处理。

在这种情况下，任务函数将写入一个文件（模拟发送电子邮件）。

由于写操作不使用 `async` 和 `await`，我们用普通的 `def` 定义函数：

{* ../../docs_src/background_tasks/tutorial001.py hl[6:9] *}

## 添加后台任务

在你的 *路径操作函数* 里，用 `.add_task()` 方法将任务函数传到 *后台任务* 对象中：

{* ../../docs_src/background_tasks/tutorial001.py hl[14] *}

En este caso, la función de tarea escribirá en un archivo (simulando el envío de un email).

Y como la operación de escritura no usa `async` y `await`, definimos la función con un `def` normal:

{* ../../docs_src/background_tasks/tutorial001_py39.py hl[6:9] *}

## Agregar la tarea en segundo plano { #add-the-background-task }

            return "Free up disk space or use a different location";
        case QUOTA:
            return "Contact administrator to increase quota limits";
        case LOCK:
            return "Release existing locks or wait for them to be released";
        case BUFFER:
            return "Reduce buffer usage or increase buffer pool size";
        case THREAD_POOL:
            return "Reduce concurrent operations or increase thread pool size";

2. Start Prometheus server and AlertManager
3. Bring down couple of MinIO instances to bring down the Erasure Set tolerance to -1 and verify the same with `mc admin prometheus metrics ALIAS | grep minio_cluster_health_erasure_set_status`
4. Wait for 5 mins (as alert is configured to be firing after 5 mins), and verify that you see an entry in webhook for the alert as well as in Prometheus console as shown below

```json
{
  "receiver": "web\\.hook",

    /**
     * Context object containing crawler state and configuration.
     */
    protected CrawlerContext crawlerContext;

    /**
     * Flag indicating whether to wait on folder operations.
     */
    protected boolean noWaitOnFolder = false;

    /**
     * Increments the active thread count.
     */
    protected void startCrawling() {