interface Backend {
    fun nanoTime(): Long

    fun coordinatorNotify(taskRunner: TaskRunner)

    fun coordinatorWait(
      taskRunner: TaskRunner,
      nanos: Long,
    )

    fun <T> decorate(queue: BlockingQueue<T>): BlockingQueue<T>

    fun execute(
      taskRunner: TaskRunner,
      runnable: Runnable,
    )
  }

  class RealBackend(
    threadFactory: ThreadFactory,

          <version>2.0.0+</version>
          <type>String</type>
          <defaultValue><![CDATA[]]></defaultValue>
          <description><![CDATA[If specified, identifies this phase as a dynamic phase to decorate the specified phase id, e.g. {@code after} or {@code before}.]]></description>
        </field>
        <field xml.attribute="true">
          <name>priority</name>
          <required>false</required>

          if (waitingCoordinatorInterrupted) {
            waitingCoordinatorInterrupted = false
            throw InterruptedException()
          }
        }

        override fun <T> decorate(queue: BlockingQueue<T>) = TaskFakerBlockingQueue(queue)
      },
      logger = logger,
    )

  /** Runs all tasks that are ready. Used by the test thread only. */
  fun runTasks() {

And it also includes a default exception handler for it.

To override it, import the `RequestValidationError` and use it with `@app.exception_handler(RequestValidationError)` to decorate the exception handler.

The exception handler will receive a `Request` and the exception.

{* ../../docs_src/handling_errors/tutorial004_py310.py hl[2,14:19] *}

   * right before each task is run. The renaming is best effort, if a {@link SecurityManager}
   * prevents the renaming then it will be skipped but the tasks will still execute.
   *
   * @param executor The executor to decorate
   * @param nameSupplier The source of names for each task
   */
  @J2ktIncompatible
  @GwtIncompatible // concurrency
  static Executor renamingDecorator(Executor executor, Supplier<String> nameSupplier) {

                    .get());
            options.addOption(Option.builder()
                    .longOpt(RAW_STREAMS)
                    .desc("Do not decorate standard output and error streams")
                    .get());
            options.addOption(Option.builder(SHOW_VERSION)
                    .longOpt("show-version")

  /**
   * Results are posted here as they occur. The find job is done when either one plan completes
   * successfully or all plans fail.
   */
  private val connectResults = taskRunner.backend.decorate(LinkedBlockingDeque<ConnectResult>())

  override fun find(): RealConnection {
    var firstException: IOException? = null
    try {
      while (tcpConnectsInFlight.isNotEmpty() || routePlanner.hasNext()) {

Ve bunun için varsayılan bir exception handler da içerir.

Override etmek için `RequestValidationError`’ı import edin ve exception handler’ı `@app.exception_handler(RequestValidationError)` ile decorate edin.

Exception handler, bir `Request` ve exception’ı alır.

{* ../../docs_src/handling_errors/tutorial004_py310.py hl[2,14:19] *}

Artık `/items/foo`’ya giderseniz, şu varsayılan JSON hatası yerine:

* [`@contextlib.asynccontextmanager`](https://docs.python.org/3/library/contextlib.html#contextlib.asynccontextmanager)

Bunları, tek bir `yield` içeren bir fonksiyonu decorate etmek için kullanabilirsiniz.

FastAPI, `yield` kullanan dependency'ler için içeride bunu yapar.

Ancak FastAPI dependency'leri için bu decorator'ları kullanmak zorunda değilsiniz (hatta kullanmamalısınız).

        def decorator(func: DecoratedCallable) -> DecoratedCallable:
            self.add_route(
                path,
                func,
                methods=methods,
                name=name,
                include_in_schema=include_in_schema,
            )
            return func

        return decorator

    def add_api_route(
        self,