8. 注意，*路径操作函数*使用的是普通函数，不是异步函数；

    与往常一样，在 FastAPI 中，可以按需组合普通函数与异步函数；

    如果不清楚何时使用异步函数或普通函数，请参阅**急不可待？**一节中对 <a href="https://fastapi.tiangolo.com/async/#in-a-hurry" target="_blank" class="internal-link">`async` 与 `await`</a> 的说明；

9. *路径操作函数*返回的不是数据类（虽然它可以返回数据类），而是返回内含数据的字典列表；

    FastAPI 使用（包含数据类的） `response_model` 参数转换响应。

把 `dataclasses` 与其它类型注解组合在一起，可以组成不同形式的复杂数据结构。

更多内容详见上述代码内的注释。

## 深入学习

	watcher *fsnotify.Watcher
	Events  chan struct{}
	Errors  chan error
}

// Waits until a file is modified (returns nil), the context is cancelled (returns context error), or returns error
func (w *Watcher) Wait(ctx context.Context) error {
	select {
	case <-w.Events:
		return nil
	case err := <-w.Errors:
		return err
	case <-ctx.Done():
		return ctx.Err()
	}
}

func (w *Watcher) Close() {

	// However, if they do get in a state where they call us in a loop, we will quickly OOM
	limit := rate.NewLimiter(rate.Limit(5), 1)
	for {
		log.Debug("accepting conn")
		if err := limit.Wait(ctx); err != nil {
			log.Errorf("failed to wait for ztunnel connection: %v", err)
			return
		}
		conn, err := z.accept()
		if err != nil {
			if errors.Is(err, net.ErrClosed) {
				log.Debug("listener closed - returning")

        "R0.20, R0.10, R0.10, R0.10"); // #7 (cont.), note, this matches #5
  }

  public void testBurstyAndUpdate() {
    RateLimiter rateLimiter = RateLimiter.create(1.0, stopwatch);
    rateLimiter.acquire(1); // no wait
    rateLimiter.acquire(1); // R1.00, to repay previous

    rateLimiter.setRate(2.0); // update the rate!

    rateLimiter.acquire(1); // R1.00, to repay previous (the previous was under the old rate!)

        "R0.20, R0.10, R0.10, R0.10"); // #7 (cont.), note, this matches #5
  }

  public void testBurstyAndUpdate() {
    RateLimiter rateLimiter = RateLimiter.create(1.0, stopwatch);
    rateLimiter.acquire(1); // no wait
    rateLimiter.acquire(1); // R1.00, to repay previous

    rateLimiter.setRate(2.0); // update the rate!

    rateLimiter.acquire(1); // R1.00, to repay previous (the previous was under the old rate!)

    🕧, FastAPI 👆 💪 🌀 `def` & `async def` 💪.

    🚥 👆 💪 ↗️ 🔃 🕐❔ ⚙️ ❔, ✅ 👅 📄 _"🏃 ❓" _ 🩺 🔃 <a href="https://fastapi.tiangolo.com/async/#in-a-hurry" target="_blank" class="internal-link">`async` &amp; `await`</a>.

9️⃣. 👉 *➡ 🛠️ 🔢* 🚫 🛬 🎻 (👐 ⚫️ 💪), ✋️ 📇 📖 ⏮️ 🔗 💽.

    FastAPI 🔜 ⚙️ `response_model` 🔢 (👈 🔌 🎻) 🗜 📨.

👆 💪 🌀 `dataclasses` ⏮️ 🎏 🆎 ✍ 📚 🎏 🌀 📨 🏗 📊 📊.

✅-📟 ✍ 💁‍♂ 🔛 👀 🌅 🎯 ℹ.

message LeaseSpec {
  // holderIdentity contains the identity of the holder of a current lease.
  // +optional
  optional string holderIdentity = 1;

  // leaseDurationSeconds is a duration that candidates for a lease need
  // to wait to force acquire it. This is measure against time of last
  // observed renewTime.
  // +optional
  optional int32 leaseDurationSeconds = 2;

  // acquireTime is a time when the current lease was acquired.
  // +optional

Dans cet exemple, la fonction de tâche écrira dans un fichier (afin de simuler un envoi d'email).

L'opération d'écriture n'utilisant ni `async` ni `await`, on définit la fonction avec un `def` normal.

{* ../../docs_src/background_tasks/tutorial001.py hl[6:9] *}

## Ajouter une tâche d'arrière-plan

  /**
   * Asserts that a prior call that had caused this thread to block or wait has since returned
   * normally.
   */
  public void assertPriorCallReturns(@Nullable String methodName) throws Exception {
    assertEquals(null, getResponse(methodName).getResult());
  }

  /**
   * Asserts that a prior call that had caused this thread to block or wait has since returned the
   * expected boolean value.
   */

        override fun onFailure(
          hostname: String,
          e: IOException,
        ) {
          exception = e
          latch.countDown()
        }
      },
    )

    latch.await()

    return Pair(allAddresses, exception)
  }

  @Test
  fun testDnsRequestExternal() {
    assumeNetwork()

    val (allAddresses, exception) = dnsQuery("google.com")