return map[string]uint64{}, nil
	}

	cache := dataUsageCache{}

	prefixUsageCache.InitOnce(30*time.Second,
		// No need to fail upon Update() error, fallback to old value.
		cachevalue.Opts{ReturnLastGood: true, NoWait: true},
		func(ctx context.Context) (map[string]uint64, error) {
			m := make(map[string]uint64)
			for _, pool := range z.serverPools {
				for _, er := range pool.sets {
					// Load bucket usage prefixes

      Future<?> possiblyIgnoredError = executorService.submit(executeTask);
      returnValue += (int) listenerLatch.getCount();
      listenerLatch.await();
    }
    return returnValue;
  }

  @Benchmark
  int executeThenAdd_multiThreaded(final int reps) throws InterruptedException {
    Runnable addTask =
        new Runnable() {
          @Override

                this.inFlightLookups.add(name);
                return null;
            }
            while ( this.inFlightLookups.contains(name) ) {
                try {
                    this.inFlightLookups.wait();
                }
                catch ( InterruptedException e ) {
                    log.trace("Interrupted", e);
                }
            }
        }
        obj = getCachedAddress(name);

./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 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 {

			manager.debugMsg(debugShutdown)
		}
		for _, server := range t.Servers {
			server.Close()
		}
		for _, listener := range t.Listeners {
			listener.Close()
		}
	})
}

// WaitAllConnect will wait for all connections to be established.
func (t *TestGrid) WaitAllConnect(ctx context.Context) {
	for _, manager := range t.Managers {
		for _, remote := range manager.Targets() {
			if manager.HostName() == remote {

В нашем примере фоновая задача будет вести запись в файл (симулируя отправку письма).

Так как операция записи не использует `async` и `await`, мы определим ее как обычную `def`:

```Python hl_lines="6-9"
{!../../docs_src/background_tasks/tutorial001.py!}
```

## Добавление фоновой задачи

					return
				}
			}

			// All versions resulted in 'ObjectNotFound/VersionNotFound'
			if versionNotFound == len(fivs.Versions) {
				return
			}

			send(healEntryDone(entry.name))

			// Wait and proceed if there are active requests
			waitForLowHTTPReq()
		}

		// How to resolve partial results.
		resolver := metadataResolutionParams{
			dirQuorum: 1,
			objQuorum: 1,
			bucket:    bucket,

**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：

```Python hl_lines="6-9"
{!../../docs_src/background_tasks/tutorial001.py!}
```

## 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：

```Python hl_lines="14"

    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():