# Concurrency and async / await { #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? { #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()
```

 * them as a {@link String}. Example:
 *
 * {@snippet :
 * Joiner joiner = Joiner.on("; ").skipNulls();
 *  . . .
 * return joiner.join("Harry", null, "Ron", "Hermione");
 * }
 *
 * <p>This returns the string {@code "Harry; Ron; Hermione"}. Note that all input elements are
 * converted to strings using {@link Object#toString()} before being appended.
 *

 * them as a {@link String}. Example:
 *
 * {@snippet :
 * Joiner joiner = Joiner.on("; ").skipNulls();
 *  . . .
 * return joiner.join("Harry", null, "Ron", "Hermione");
 * }
 *
 * <p>This returns the string {@code "Harry; Ron; Hermione"}. Note that all input elements are
 * converted to strings using {@link Object#toString()} before being appended.
 *

@app.get("/items/{item_id}")
async def read_item(item_id: int, q: Union[str, None] = None):
    return {"item_id": item_id, "q": q}
```

**Przypis**:

Jeżeli nie znasz, sprawdź sekcję _"In a hurry?"_ o <a href="https://fastapi.tiangolo.com/async/#in-a-hurry" target="_blank">`async` i `await` w dokumentacji</a>.

</details>

### Uruchom

Uruchom serwer używając:

<div class="termy">

```console

of the bottle was a paper label, with the words `DRINK ME'
beautifully printed on it in large letters.

  It was all very well to say `Drink me,' but the wise little
Alice was not going to do THAT in a hurry.  `No, I'll look
first,' she said, `and see whether it's marked "poison" or not';
for she had read several nice little histories about children who
had got burnt, and eaten up by wild beasts and other unpleasant

@app.get("/items/{item_id}")
async def read_item(item_id: int, q: Union[str, None] = None):
    return {"item_id": item_id, "q": q}
```

**Lưu ý**:

Nếu bạn không biết, xem phần _"In a hurry?"_ về <a href="https://fastapi.tiangolo.com/async/#in-a-hurry" target="_blank">`async` và `await` trong tài liệu này</a>.

</details>

### Chạy ứng dụng

Chạy server như sau:

<div class="termy">

```console

@app.get("/items/{item_id}")
async def read_item(item_id: int, q: Optional[str] = None):
    return {"item_id": item_id, "q": q}
```

**Nota**:

e vuoi approfondire, consulta la sezione  _"In a hurry?"_ su <a href="https://fastapi.tiangolo.com/async/#in-a-hurry" target="_blank">`async` e `await` nella documentazione</a>.

</details>

### Esegui il server

Puoi far partire il server così:

<div class="termy">

```console

Это всё не важно. **FastAPI** знает, что нужно сделать. 😎

/// note | Информация

Если вам эта тема не знакома, прочтите [Async: *"In a hurry?"*](../../async.md){.internal-link target=_blank} раздел о `async` и `await` в документации.

///

## Интеграция с OpenAPI

import junit.framework.TestCase;
import org.jspecify.annotations.NullMarked;
import org.jspecify.annotations.Nullable;

/**
 * Tests com.google.common.base.Suppliers.
 *
 * @author Laurence Gonsalves
 * @author Harry Heymann
 */
@NullMarked
@GwtCompatible
public class SuppliersTest extends TestCase {

  static class CountingSupplier implements Supplier<Integer> {
    int calls = 0;

    @Override

No importa. **FastAPI** sabrá qué hacer.

/// note | Nota

Si no lo sabes, revisa la sección [Async: *"¿Con prisa?"*](../../async.md#in-a-hurry){.internal-link target=_blank} sobre `async` y `await` en la documentación.

///

## Integración con OpenAPI