responses={404: {"description": "Not found"}},
)


fake_items_db = {"plumbus": {"name": "Plumbus"}, "gun": {"name": "Portal Gun"}}


@router.get("/")
async def read_items():
    return fake_items_db


@router.get("/{item_id}")
async def read_item(item_id: str):
    if item_id not in fake_items_db:
        raise HTTPException(status_code=404, detail="Item not found")

            return response

        return custom_route_handler


app = FastAPI()
router = APIRouter(route_class=TimedRoute)


@app.get("/")
async def not_timed():
    return {"message": "Not timed"}


@router.get("/timed")
async def timed():
    return {"message": "It's the time of my life"}

echo 1 > /proc/sys/kernel/perf_event_paranoid
exit
```

Grab the async profiler from https://github.com/jvm-profiling-tools/async-profiler
and run `prof async` like so:
```
gradlew -p benchmarks/ run --args 'LongKeyedBucketOrdsBenchmark.multiBucket -prof "async:libPath=/home/nik9000/Downloads/tmp/async-profiler-1.8.3-linux-x64/build/libasyncProfiler.so;dir=/tmp/prof;output=flamegraph"'
```

# Streaming

## Stream JSON Lines

To stream JSON Lines, declare the return type and use `yield` to return the data.

```python
@app.get("/items/stream")
async def stream_items() -> AsyncIterable[Item]:
    for item in items:
        yield item
```

## Server-Sent Events (SSE)

To stream Server-Sent Events, use `response_class=EventSourceResponse` and `yield` items from the endpoint.

## To `async` or not to `async` { #to-async-or-not-to-async }

As dependencies will also be called by **FastAPI** (the same as your *path operation functions*), the same rules apply while defining your functions.

You can use `async def` or normal `def`.

Dikkat edilmesi gereken ilk şey, `yield` içeren async bir fonksiyon tanımlıyor olmamız. Bu, `yield` kullanan Dependencies’e oldukça benzer.

{* ../../docs_src/events/tutorial003_py310.py hl[14:19] *}

Fonksiyonun `yield`’den önceki kısmı, uygulama başlamadan **önce** çalışır.

`yield`’den sonraki kısım ise, uygulama işini bitirdikten **sonra** çalışır.

### Async Context Manager { #async-context-manager }

app = FastAPI()


async def common_parameters(q: str | None = None, skip: int = 0, limit: int = 100):
    return {"q": q, "skip": skip, "limit": limit}


@app.get("/items/")
async def read_items(commons: Annotated[dict, Depends(common_parameters)]):
    return {"message": "Hello Items!", "params": commons}


@app.get("/users/")
async def read_users(commons: Annotated[dict, Depends(common_parameters)]):

from fastapi import FastAPI

app = FastAPI()


@app.get("/items/", tags=["items"])
async def read_items():
    return [{"name": "Foo", "price": 42}]


@app.get("/users/", tags=["users"])
async def read_users():
    return [{"username": "johndoe"}]


@app.get("/elements/", tags=["items"], deprecated=True)
async def read_elements():

                throw new RuntimeException(e);
            }
        }

        @Override
        public boolean isAsync() {
            return async;
        }

        public void setAsync(boolean async) {
            this.async = async;
        }

        @Override
        public boolean isRetainPayload() {
            return retainPayload;
        }

### Lifespan 函式 { #lifespan-function }

首先要注意的是，我們定義了一個帶有 `yield` 的 async 函式。這和帶有 `yield` 的依賴（Dependencies）非常相似。

{* ../../docs_src/events/tutorial003_py310.py hl[14:19] *}

函式在 `yield` 之前的部分，會在應用啟動前先執行。

`yield` 之後的部分，會在應用結束後再執行。

### 非同步內容管理器（Async Context Manager） { #async-context-manager }

你會看到這個函式被 `@asynccontextmanager` 裝飾。

它會把函式轉換成所謂的「**非同步內容管理器（async context manager）**」。