# Concurrencia y async / await { #concurrency-and-async-await }

Detalles sobre la sintaxis `async def` para *path operation functions* y algunos antecedentes sobre el código asíncrono, la concurrencia y el paralelismo.

## ¿Con prisa? { #in-a-hurry }

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

Si estás usando paquetes de terceros que te dicen que los llames con `await`, como:

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

                    response = await f(request)
                await response(scope, receive, send)
                # Continues customization
                response_awaited = True
            if not response_awaited:
                raise FastAPIError(
                    "Response not awaited. There's a high chance that the "

    waiter2.join();
  }

  public void testRemoveWaiter_polling() throws Exception {
    AbstractFuture<String> future = new AbstractFuture<String>() {};
    WaiterThread waiter = new WaiterThread(future);
    waiter.start();
    waiter.awaitWaiting();
    PollingThread poller = new PollingThread(future);
    poller.start();
    PollingThread poller2 = new PollingThread(future);
    poller2.start();

    waiter2.join();
  }

  public void testRemoveWaiter_polling() throws Exception {
    AbstractFuture<String> future = new AbstractFuture<String>() {};
    WaiterThread waiter = new WaiterThread(future);
    waiter.start();
    waiter.awaitWaiting();
    PollingThread poller = new PollingThread(future);
    poller.start();
    PollingThread poller2 = new PollingThread(future);
    poller2.start();

    Thread waiter =
        new Thread() {
          @Override
          public void run() {
            try {
              service.awaitTermination(1, DAYS);
            } catch (InterruptedException e) {
              return;
            }
          }
        };
    waiter.start();
    awaitTimedWaiting(waiter);
    service.shutdown();

    Thread waiter =
        new Thread() {
          @Override
          public void run() {
            try {
              service.awaitTermination(1, DAYS);
            } catch (InterruptedException e) {
              return;
            }
          }
        };
    waiter.start();
    awaitTimedWaiting(waiter);
    service.shutdown();

        try {
          latch.await();
        } catch (InterruptedException quittingTime) {
        }
        return TEST_STRING;
      }
    };
  }

  public Runnable awaiter(CountDownLatch latch) {
    return new CheckedRunnable() {
      @Override
      public void realRun() throws InterruptedException {
        await(latch);
      }
    };
  }

app = FastAPI()


@app.get("/")
async def read_main():
    return {"msg": "Hello World"}


@app.websocket("/ws")
async def websocket(websocket: WebSocket):
    await websocket.accept()
    await websocket.send_json({"msg": "Hello WebSocket"})
    await websocket.close()


def test_read_main():
    client = TestClient(app)
    response = client.get("/")
    assert response.status_code == 200

</html>
"""


@app.get("/")
async def get():
    return HTMLResponse(html)


@app.websocket("/ws")
async def websocket_endpoint(websocket: WebSocket):
    await websocket.accept()
    while True:
        data = await websocket.receive_text()

@app.websocket("/function-scope")
async def function_scope(websocket: WebSocket, session: SessionFuncDep) -> Any:
    await websocket.accept()
    await websocket.send_json({"is_open": session.open})


@app.websocket("/request-scope")
async def request_scope(websocket: WebSocket, session: SessionRequestDep) -> Any:
    await websocket.accept()
    await websocket.send_json({"is_open": session.open})


@app.websocket("/two-scopes")