# 並行與 async / await

有關*路徑操作函式*的 `async def` 語法的細節與非同步 (asynchronous) 程式碼、並行 (concurrency) 與平行 (parallelism) 的一些背景知識。

## 趕時間嗎?

<abbr title="too long; didn't read（文長慎入）"><strong>TL;DR:</strong></abbr>

如果你正在使用要求你以 `await` 語法呼叫的第三方函式庫，例如：

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

然後，使用 `async def` 宣告你的*路徑操作函式*：


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

* `seek(offset)`: Переміщується до позиції `offset` (`int`) у файлі.
    * Наприклад, `await myfile.seek(0)` поверне курсор на початок файлу.
    * This is especially useful if you run `await myfile.read()` once and then need to read the contents again. Це особливо корисно, якщо Ви виконуєте await `await myfile.read()` один раз, а потім потрібно знову прочитати вміст.
* `close()`: Закриває файл.

        });
        th.start();

        final CountDownLatch latch = new CountDownLatch(1);
        deferred.promise().then(response -> latch.countDown());
        assertTrue(latch.await(10, TimeUnit.SECONDS));
    }

    @Test
    public void test_doneAfterResolve() throws Exception {
        final Deferred<SuggestResponse> deferred = new Deferred<>();

        Thread th = new Thread(() -> {

            // that the stream has since been closed (such as if this write timed out.)
            if (!streams.containsKey(streamId)) {
              throw IOException("stream closed")
            }
            wait() // Wait until we receive a WINDOW_UPDATE.
          }
        } catch (e: InterruptedException) {
          Thread.currentThread().interrupt() // Retain interrupted status.
          throw InterruptedIOException()
        }

package clause

const (
	LockingStrengthUpdate    = "UPDATE"
	LockingStrengthShare     = "SHARE"
	LockingOptionsSkipLocked = "SKIP LOCKED"
	LockingOptionsNoWait     = "NOWAIT"
)

type Locking struct {
	Strength string
	Table    Table
	Options  string
}

// Name where clause name
func (locking Locking) Name() string {
	return "FOR"
}

// Build build where clause
func (locking Locking) Build(builder Builder) {

Luego podemos crear un `AsyncClient` con la app y enviar requests asíncronos a ella, usando `await`.

{* ../../docs_src/async_tests/test_main.py hl[9:12] *}

Esto es equivalente a:

```Python
response = client.get('/')
```

...que usábamos para hacer nuestros requests con el `TestClient`.

/// tip | Consejo

Nota que estamos usando async/await con el nuevo `AsyncClient`: el request es asíncrono.

///

   */
  public void assertSuccess(Object expectedData) throws Throwable {
    // Verify that the listener executed in a reasonable amount of time.
    Assert.assertTrue(countDownLatch.await(1L, SECONDS));

    try {
      Assert.assertEquals(expectedData, future.get());
    } catch (ExecutionException e) {
      throw e.getCause();
    }
  }

  /**

    assertTrue(latch.await(5, SECONDS));
    assertTrue(future.isDone());
    assertFalse(future.isCancelled());

    assertEquals(expectedValue, future.get());
  }

  public void testCancelledFuture() throws InterruptedException, ExecutionException {
    assertTrue(future.isDone());
    assertTrue(future.isCancelled());

    assertTrue(latch.await(5, SECONDS));
    assertTrue(future.isDone());

* `seek(offset)`: Va a la posición de bytes `offset` (`int`) en el archivo.
    * Por ejemplo, `await myfile.seek(0)` iría al inicio del archivo.
    * Esto es especialmente útil si ejecutas `await myfile.read()` una vez y luego necesitas leer el contenido nuevamente.
* `close()`: Cierra el archivo.

Como todos estos métodos son métodos `async`, necesitas "await" para ellos.

        // Start timing
        long overallStart = System.nanoTime();

        for (int t = 0; t < threadCount; t++) {
            executor.submit(() -> {
                try {
                    startLatch.await();

                    long threadStart = System.nanoTime();
                    for (int i = 0; i < operationsPerThread; i++) {
                        try {