# 并发 async / await

有关路径操作函数的 `async def` 语法以及异步代码、并发和并行的一些背景知识。

## 赶时间吗？

<abbr title="too long; didn't read(长文警告)"><strong>TL;DR:</strong></abbr>

如果你正在使用第三方库，它们会告诉你使用 `await` 关键字来调用它们，就像这样：

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

然后，通过 `async def` 声明你的 *路径操作函数*：

```Python hl_lines="2"
@app.get('/')
async def read_results():
    results = await some_library()
    return results
```

/// note

# 동시성과 async / await

*경로 작동 함수*에서의 `async def` 문법에 대한 세부사항과 비동기 코드, 동시성 및 병렬성에 대한 배경

## 바쁘신 경우

<strong>요약</strong>

다음과 같이 `await`를 사용해 호출하는 제3의 라이브러리를 사용하는 경우:

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

다음처럼 *경로 작동 함수*를 `async def`를 사용해 선언하십시오:

```Python hl_lines="2"
@app.get('/')
async def read_results():
    results = await some_library()
    return results
```

/// note | "참고"

          @Override
          protected void finalize() {
            latch.countDown();
          }
        };
    unused = null; // Hint to the JIT that unused is unreachable
    GcFinalization.await(latch);
    assertEquals(0, latch.getCount());
  }

  public void testAwaitDone_future() {
    final SettableFuture<@Nullable Void> future = SettableFuture.create();
    Object unused =
        new Object() {

async def custom_http_exception_handler(request, exc):
    print(f"OMG! An HTTP error!: {repr(exc)}")
    return await http_exception_handler(request, exc)


@app.exception_handler(RequestValidationError)
async def validation_exception_handler(request, exc):
    print(f"OMG! The client sent invalid data!: {exc}")
    return await request_validation_exception_handler(request, exc)


@app.get("/items/{item_id}")

import * as fs from 'fs'

async function modifyOpenAPIFile(filePath) {
  try {
    const data = await fs.promises.readFile(filePath)
    const openapiContent = JSON.parse(data)

    const paths = openapiContent.paths
    for (const pathKey of Object.keys(paths)) {
      const pathData = paths[pathKey]
      for (const method of Object.keys(pathData)) {
        const operation = pathData[method]
        if (operation.tags && operation.tags.length > 0) {

* `seek(offset)`: Goes to the byte position `offset` (`int`) in the file.
    * E.g., `await myfile.seek(0)` would go to the start of the file.
    * This is especially useful if you run `await myfile.read()` once and then need to read the contents again.
* `close()`: Closes the file.

As all these methods are `async` methods, you need to "await" them.

For example, inside of an `async` *path operation function* you can get the contents with:

      thread.start();
      // we want to wait until each thread is WAITING - one thread waiting inside CacheLoader.load
      // (in startSignal.await()), and the others waiting for that thread's result.
      while (thread.isAlive() && thread.getState() != Thread.State.WAITING) {
        Thread.yield();
      }
    }
    gettersStartedSignal.countDown();
    gettersComplete.await();

import time

from fastapi import FastAPI, Request

app = FastAPI()


@app.middleware("http")
async def add_process_time_header(request: Request, call_next):
    start_time = time.perf_counter()
    response = await call_next(request)
    process_time = time.perf_counter() - start_time
    response.headers["X-Process-Time"] = str(process_time)

from .main import app


@pytest.mark.anyio
async def test_root():
    async with AsyncClient(
        transport=ASGITransport(app=app), base_url="http://test"
    ) as ac:
        response = await ac.get("/")
    assert response.status_code == 200

@app.websocket("/items/{item_id}")
async def websocket_item(item_id: str, websocket: WebSocket):
    route: APIWebSocketRoute = websocket.scope["route"]
    await websocket.accept()
    await websocket.send_json({"item_id": item_id, "path": route.path})


client = TestClient(app)


def test_get():
    response = client.get("/users/rick")