!!! tip
    Notice that here as we are using standard `open()` that doesn't support `async` and `await`, we declare the path operation with normal `def`.

### `FileResponse`

Asynchronously streams a file as the response.

Takes a different set of arguments to instantiate than the other response types:

* `path` - The filepath to the file to stream.

        .build()
    val responseB = client.newCall(requestB).execute()
    assertThat(responseB.body.string()).isEqualTo("b")
  }

  /** Make sure interceptors can interact with the OkHttp client asynchronously.  */
  @Test
  fun interceptorMakesAnUnrelatedAsyncRequest() {
    server.enqueue(MockResponse.Builder().body("a").build()) // Fetched by interceptor.

* **Asynchronous Code**
* **`async` and `await`**
* **Coroutines**

## Asynchronous Code

Asynchronous code just means that the language 💬 has a way to tell the computer / program 🤖 that at some point in the code, it 🤖 will have to wait for *something else* to finish somewhere else. Let's say that *something else* is called "slow-file" 📝.

So, during that time, the computer can go and do some other work, while "slow-file" 📝 finishes.

      receivedCloseCode = code
      receivedCloseReason = reason
    }

    listener.onClosing(this, code, reason)
  }

  // Writer methods to enqueue frames. They'll be sent asynchronously by the writer thread.

  override fun send(text: String): Boolean {
    return send(text.encodeUtf8(), OPCODE_TEXT)
  }

  override fun send(bytes: ByteString): Boolean {

  internal var nextStreamId = if (builder.client) 3 else 2

  private var isShutdown = false

  /** For scheduling everything asynchronous. */
  private val taskRunner = builder.taskRunner

  /** Asynchronously writes frames to the outgoing socket. */
  private val writerQueue = taskRunner.newQueue()

  /** Ensures push promise callbacks events are sent in order per stream. */

def read_user(user_id: int, db: Session = Depends(get_db)):
    db_user = crud.get_user(db, user_id=user_id)
    ...
```

!!! info
    If you need to connect to your relational database asynchronously, see [Async SQL (Relational) Databases](../how-to/async-sql-encode-databases.md){.internal-link target=_blank}.

!!! note "Very Technical Details"

    if (delegate.isDone()) {
      return delegate;
    }
    return TimeoutFuture.create(delegate, time, unit, scheduledExecutor);
  }

  /**
   * Returns a new {@code Future} whose result is asynchronously derived from the result of the
   * given {@code Future}. If the given {@code Future} fails, the returned {@code Future} fails with
   * the same exception (and the function is not invoked).
   *

// deleted/overwritten version. This version is visible _only_to the scanner routine, for subsequent deletion.
// This kind of tracking is necessary since a version's tiered content is deleted asynchronously.

// Backend directory tree structure:
// disk1/
// └── bucket
//     └── object
//         ├── a192c1d5-9bd5-41fd-9a90-ab10e165398d
//         │   └── part.1

   * @throws IllegalArgumentException if {@code duration} is negative
   * @throws IllegalStateException if {@link #refreshAfterWrite} was already set
   * @since 11.0
   */
  @GwtIncompatible // To be supported (synchronously).
  @SuppressWarnings("GoodTime") // should accept a java.time.Duration
  @CanIgnoreReturnValue
  public CacheBuilder<K, V> refreshAfterWrite(long duration, TimeUnit unit) {
    checkNotNull(unit);

   * @throws IllegalArgumentException if {@code duration} is negative
   * @throws IllegalStateException if {@link #refreshAfterWrite} was already set
   * @since 11.0
   */
  @GwtIncompatible // To be supported (synchronously).
  @SuppressWarnings("GoodTime") // should accept a java.time.Duration
  @CanIgnoreReturnValue
  public CacheBuilder<K, V> refreshAfterWrite(long duration, TimeUnit unit) {
    checkNotNull(unit);