Although the [Tutorial - User Guide](../tutorial/index.md){.internal-link target=_blank} and this **Advanced User Guide** are written as a guided tutorial (like a book) and should be enough for you to **learn FastAPI**, you might want to complement it with additional courses.

Or it might be the case that you just prefer to take other courses because they adapt better to your learning style.

 * instance for non-daemon threads.
 *
 * The task runner is also responsible for releasing held threads when the library is unloaded.
 * This is for the benefit of container environments that implement code unloading.
 *
 * Most applications should share a process-wide [TaskRunner] and use queues for per-client work.
 */
class TaskRunner(
  val backend: Backend,
  internal val logger: Logger = TaskRunner.logger,

 * may ultimately cause the application to slow down or crash.
 *
 * Both this class and [Response] implement [Closeable]. Closing a response simply
 * closes its response body. If you invoke [Call.execute] or implement [Callback.onResponse] you
 * must close this body by calling any of the following methods:
 *
 * * `Response.close()`
 * * `Response.body().close()`

## Version 1.5.3

_2014-03-29_

 * Fix bug where the Content-Length header was not always dropped when
   following a redirect from a POST to a GET.
 * Implement basic support for `Thread.interrupt()`. OkHttp now checks
   for an interruption before doing a blocking call. If it is interrupted,
   it throws an `InterruptedIOException`.

## Version 1.5.2

_2014-03-17_

- To be able to reliably use S3 multipart APIs feature of the SDKs without re-inventing the wheel of pre-signing the each URL in multipart API. This is very tedious to implement with all the scenarios of fault tolerance that's already implemented by the client SDK. The general client SDKs don't support multipart with presigned URLs.

#### Caching

- [`KT-56943`](https://youtrack.jetbrains.com/issue/KT-56943) K/Wasm: implement `@WasmImport` diagnostics
- [`KT-55903`](https://youtrack.jetbrains.com/issue/KT-55903) K2: False negative CANNOT_CHECK_FOR_ERASED on is-check for type with reified type arguments
- [`KT-56944`](https://youtrack.jetbrains.com/issue/KT-56944) K/Wasm: implement `@JsFun` diagnostics

That documentation will show up in the Swagger UI at `/docs` in your API, and it will let external developers know how to build the *external API*.

This example doesn't implement the callback itself (that could be just a line of code), only the documentation part.

!!! tip
    The actual callback is just an HTTP request.

 *  **OkHttp now supports duplex calls over HTTP/2.** With normal HTTP calls the request must finish
    before the response starts. With duplex, request and response bodies are transmitted
    simultaneously. This can be used to implement interactive conversations within a single HTTP
    call.

    Create duplex calls by overriding the new `RequestBody.isDuplex()` method to return true.

You will get an "Inactive user" error, like:

```JSON
{
  "detail": "Inactive user"
}
```

## Recap

You now have the tools to implement a complete security system based on `username` and `password` for your API.

Using these tools, you can make the security system compatible with any database and with any user or data model.