# Background Tasks { #background-tasks }

You can define background tasks to be run *after* returning a response.

This is useful for operations that need to happen after a request, but that the client doesn't really have to be waiting for the operation to complete before receiving the response.

This includes, for example:

* Email notifications sent after performing an action:

            <goals>
              <goal>manifest</goal>
            </goals>
          </execution>
        </executions>
        <configuration>
          <instructions>
            <!-- Silence a warning that claims that META-INF/versions/9/... is the "wrong directory" for our classes. -->
            <_fixupmessages>^Classes found in the wrong directory: .*</_fixupmessages>

* For `PUT` requests to `/items/{item_id}`, read the body as JSON:
    * Check that it has a required attribute `name` that should be a `str`.
    * Check that it has a required attribute `price` that has to be a `float`.
    * Check that it has an optional attribute `is_offer`, that should be a `bool`, if present.
    * All this would also work for deeply nested JSON objects.

        // Test that custom sessionId is sanitized
        Crawler.Options options = new Crawler.Options();
        options.sessionId = "test-session-123";

        // Simulate what process() does - sanitize sessionId
        if (options.sessionId != null) {
            options.sessionId = options.sessionId.replaceAll("-", "_");
        }

That information is available in the app's **OpenAPI schema**, and then shown in the API docs.

That same information from the models that is included in OpenAPI is what can be used to **generate the client code**.

### Hey API { #hey-api }

Once we have a FastAPI app with the models, we can use Hey API to generate a TypeScript client. The fastest way to do that is via npx.

```sh

    validations:
      required: true

  - type: textarea
    attributes:
      label: Expected Behavior
      description: What did you expect to happen?
    validations:
      required: true

  - type: textarea
    attributes:
      label: Actual Behavior
      description: What actually happened?
    validations:
      required: true

  - type: dropdown
    attributes:
      label: Packages

If you are using containers, for example with Docker or Kubernetes, I'll tell you more about that in the next chapter: [FastAPI in Containers - Docker](docker.md){.internal-link target=_blank}.

In particular, when running on **Kubernetes** you will probably **not** want to use workers and instead run **a single Uvicorn process per container**, but I'll tell you about it later in that chapter.

///

## Multiple Workers { #multiple-workers }

	"github.com/minio/pkg/v3/policy"
)

// http Header "x-amz-content-sha256" == "UNSIGNED-PAYLOAD" indicates that the
// client did not calculate sha256 of the payload.
const unsignedPayload = "UNSIGNED-PAYLOAD"

// http Header "x-amz-content-sha256" == "STREAMING-UNSIGNED-PAYLOAD-TRAILER" indicates that the
// client did not calculate sha256 of the payload and there is a trailer.

# Về các phiên bản của FastAPI

**FastAPI** đã được sử dụng ở quy mô thực tế (production) trong nhiều ứng dụng và hệ thống. Và phạm vi kiểm thử được giữ ở mức 100%. Nhưng việc phát triển của nó vẫn đang diễn ra nhanh chóng.

Các tính năng mới được bổ sung thường xuyên, lỗi được sửa định kỳ, và mã nguồn vẫn đang được cải thiện liên tục

 *
 * <p>The view collections of the returned map have <i>weakly consistent iterators</i>. This means
 * that they are safe for concurrent use, but if other threads modify the map after the iterator is
 * created, it is undefined which of these changes, if any, are reflected in that iterator. These
 * iterators never throw {@link ConcurrentModificationException}.
 *