* `expose_headers` - 指示可以被浏览器访问的响应头。默认为 `[]`。
* `max_age` - 设定浏览器缓存 CORS 响应的最长时间，单位是秒。默认为 `600`。

中间件响应两种特定类型的 HTTP 请求……

### CORS 预检请求

这是些带有 `Origin` 和 `Access-Control-Request-Method` 请求头的 `OPTIONS` 请求。

在这种情况下，中间件将拦截传入的请求并进行响应，出于提供信息的目的返回一个使用了适当的 CORS headers 的 `200` 或 `400` 响应。

### 简单请求

任何带有 `Origin` 请求头的请求。在这种情况下，中间件将像平常一样传递请求，但是在响应中包含适当的 CORS headers。

## 更多信息

import junit.framework.TestCase;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Tests for {@link ForwardingWrapperTester}. Live in a different package to detect reflection
 * access issues, if any.
 *
 * @author Ben Yu
 */
public class ForwardingWrapperTesterTest extends TestCase {

  private final ForwardingWrapperTester tester = new ForwardingWrapperTester();

For example, inside of an `async` *path operation function* you can get the contents with:

```Python
contents = await myfile.read()
```

If you are inside of a normal `def` *path operation function*, you can access the `UploadFile.file` directly, for example:

```Python
contents = myfile.file.read()
```

/// note | "`async` Technical Details"

 * row(rowKey)} and {@code rowMap().get(rowKey)} are {@link SortedMap} instances, instead of the
 * {@link Map} specified in the {@link Table} interface.
 *
 * <p>Note that this implementation is not synchronized. If multiple threads access this table
 * concurrently and one of the threads modifies the table, it must be synchronized externally.
 *
 * <p>See the Guava User Guide article on <a href=

            return count.incrementAndGet();
        }

        public int decrement() {
            return count.decrementAndGet();
        }
    }

    public enum StatsAction {
        ACCESSED, //
        ACCESS_EXCEPTION, //
        CHILD_URL, //
        CHILD_URLS, //
        EVALUATED, //
        EXCEPTION, //
        FINISHED, //
        PARSED, //
        PREPARED, //

    shift
  done
}

handle_args "$@"
MAVEN_MAIN_CLASS=${MAVEN_MAIN_CLASS:=org.apache.maven.cling.MavenCling}

exec "$JAVACMD" \
  $MAVEN_OPTS \
  $MAVEN_DEBUG_OPTS \
  --enable-native-access=ALL-UNNAMED \
  -classpath "$LAUNCHER_JAR" \
  "-Dclassworlds.conf=$CLASSWORLDS_CONF" \
  "-Dmaven.home=$MAVEN_HOME" \
  "-Dmaven.mainClass=$MAVEN_MAIN_CLASS" \
  "-Dlibrary.jline.path=${MAVEN_HOME}/lib/jline-native" \

O **FastAPI** criará o objeto do tipo `BackgroundTasks` para você e o passará como esse parâmetro.

## Criar uma função de tarefa

Crie uma função a ser executada como tarefa em segundo plano.

É apenas uma função padrão que pode receber parâmetros.

Pode ser uma função `async def` ou `def` normal, o **FastAPI** saberá como lidar com isso corretamente.

Nesse caso, a função de tarefa gravará em um arquivo (simulando o envio de um e-mail).

To see an example, check the [Project Generators](../project-generation.md){.internal-link target=_blank}, they all include Celery already configured.

But if you need to access variables and objects from the same **FastAPI** app, or you need to perform small background tasks (like sending an email notification), you can simply just use `BackgroundTasks`.

## Recap

    this.nodeOrder = builder.nodeOrder.cast();
    this.edgeOrder = builder.edgeOrder.cast();
    // Prefer the heavier "MapRetrievalCache" for nodes if lookup is expensive. This optimizes
    // methods that access the same node(s) repeatedly, such as Graphs.removeEdgesConnecting().
    this.nodeConnections =
        (nodeConnections instanceof TreeMap)
            ? new MapRetrievalCache<N, NetworkConnections<N, E>>(nodeConnections)

    this.nodeOrder = builder.nodeOrder.cast();
    this.edgeOrder = builder.edgeOrder.cast();
    // Prefer the heavier "MapRetrievalCache" for nodes if lookup is expensive. This optimizes
    // methods that access the same node(s) repeatedly, such as Graphs.removeEdgesConnecting().
    this.nodeConnections =
        (nodeConnections instanceof TreeMap)
            ? new MapRetrievalCache<N, NetworkConnections<N, E>>(nodeConnections)