{* ../../docs_src/background_tasks/tutorial002.py hl[13,15,22,25] *}

Dans cet exemple, les messages seront écrits dans le fichier `log.txt` après que la réponse soit envoyée.

S'il y avait une `query` (paramètre nommé `q`) dans la requête, alors elle sera écrite dans `log.txt` via une tâche d'arrière-plan.

Juste avant de décider de développer **FastAPI**, j'ai trouvé le serveur **APIStar**. Il contenait presque tout ce
que je recherchais et avait un beau design.

C'était l'une des premières implémentations d'un framework utilisant les type hints Python pour déclarer les paramètres

# Concurrency and async / await

Details about the `async def` syntax for *path operation functions* and some background about asynchronous code, concurrency, and parallelism.

## In a hurry?

<abbr title="too long; didn't read"><strong>TL;DR:</strong></abbr>

If you are using third party libraries that tell you to call them with `await`, like:

```Python
results = await some_library()
```

    assertTrue(listenerLatch.await(5, SECONDS));
    assertTrue(task.isDone());
    assertFalse(task.isCancelled());
  }

  public void testListenerCalledOnException() throws Exception {
    throwException = true;

    // Start up the task and unblock the latch to finish the task.
    exec.execute(task);
    runLatch.await();
    taskLatch.countDown();

    assertTrue(listenerLatch.await(5, SECONDS));
    assertTrue(task.isDone());
    assertFalse(task.isCancelled());
  }

  public void testListenerCalledOnException() throws Exception {
    throwException = true;

    // Start up the task and unblock the latch to finish the task.
    exec.execute(task);
    runLatch.await();
    taskLatch.countDown();

                }
              }
            });
    thread.start();
    enterLatch.await();
    assertFalse(task.isDone());
    task.cancel(true);
    assertTrue(task.isDone());
    assertTrue(task.isCancelled());
    assertTrue(task.wasInterrupted());
    assertThrows(CancellationException.class, () -> task.get());
    exitLatch.await();
    assertTrue(interruptedExceptionThrown.get());
  }

  @J2ktIncompatible

	<script src="../../lib/wasm/wasm_exec.js"></script>
	<script>
		if (!WebAssembly.instantiateStreaming) { // polyfill
			WebAssembly.instantiateStreaming = async (resp, importObject) => {
				const source = await (await resp).arrayBuffer();
				return await WebAssembly.instantiate(source, importObject);
			};
		}

		const go = new Go();
		let mod, inst;
		WebAssembly.instantiateStreaming(fetch("test.wasm"), go.importObject).then((result) => {

  /** Invokes {@code latch.}{@link CountDownLatch#await() await()} uninterruptibly. */
  @J2ktIncompatible
  @GwtIncompatible // concurrency
  public static void awaitUninterruptibly(CountDownLatch latch) {
    boolean interrupted = false;
    try {
      while (true) {
        try {
          latch.await();
          return;
        } catch (InterruptedException e) {

# Concurrencia y async / await

Detalles sobre la sintaxis `async def` para *path operation functions* y un poco de información sobre código asíncrono, concurrencia y paralelismo.

## ¿Tienes prisa?

<abbr title="too long; didn't read"><strong>TL;DR:</strong></abbr>

Si estás utilizando libraries de terceros que te dicen que las llames con `await`, del tipo:

```Python
results = await some_library()
```

* `read(size)`：按指定数量的字节或字符（`size` (`int`)）读取文件内容；
* `seek(offset)`：移动至文件 `offset` （`int`）字节处的位置；
    * 例如，`await myfile.seek(0) ` 移动到文件开头；
    * 执行 `await myfile.read()` 后，需再次读取已读取内容时，这种方法特别好用；
* `close()`：关闭文件。

因为上述方法都是 `async` 方法，要搭配「await」使用。

例如，在 `async` *路径操作函数* 内，要用以下方式读取文件内容：

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

在普通 `def` *路径操作函数*  内，则可以直接访问 `UploadFile.file`，例如：

```Python