* #enqueue enqueued} and {@link #dispatch dispatched}.
   */
  public void addListener(L listener, Executor executor) {
    checkNotNull(listener, "listener");
    checkNotNull(executor, "executor");
    listeners.add(new PerListenerQueue<>(listener, executor));
  }

  /**
   * Enqueues an event to be run on currently known listeners.
   *

    }

    if (failFastResponse != null && responseQueue.peek() == null) {
      // Fail fast if there's no response queued up.
      return failFastResponse!!
    }

    val result = responseQueue.take()

    // If take() returned because we're shutting down, then enqueue another dead letter so that any
    // other threads waiting on take() will also return.
    if (result == DEAD_LETTER) responseQueue.add(DEAD_LETTER)

   * that enqueued messages were not transmitted.
   */
  fun queueSize(): Long

  /**
   * Attempts to enqueue `text` to be UTF-8 encoded and sent as a the data of a text (type `0x1`)
   * message.
   *
   * This method returns true if the message was enqueued. Messages that would overflow the outgoing

  // instance for every unit test.
  MockWebServer server = new MockWebServer();

  // Schedule some responses.
  server.enqueue(new MockResponse.Builder()
      .body("hello, world!")
      .build());
  server.enqueue(new MockResponse.Builder()
      .body("sup, bra?")
      .build());
  server.enqueue(new MockResponse.Builder()
      .body("yo dog")
      .build());

  // Start the server.
  server.start();

   *
   * @throws IllegalStateException when the call has already been executed.
   */
  fun enqueue(responseCallback: Callback)

  /** Cancels the request, if possible. Requests that are already complete cannot be canceled. */
  fun cancel()

  /**
   * Returns true if this call has been either [executed][execute] or [enqueued][enqueue]. It is an
   * error to execute a call more than once.
   */
  fun isExecuted(): Boolean

        }
    }
  }

  companion object {
    /**
     * Enqueues a [Call] and process it as [EventSource] with [listener].
     */
    @JvmStatic
    @JvmName("enqueue")
    fun Call.enqueueEventSource(listener: EventSourceListener): EventSource = RealEventSource(this, listener).also(this::enqueue)

    /**
     * Processes the existing response with [listener].
     */
    @JvmStatic

    // makeSimpleCall() because it uses the MockResponse enqueued above.
    val callB = client.newCall(Request(server.url("/")))
    callB.execute().use { response ->
      assertThat(response.body.string()).isEqualTo("abc")
    }
  }

  private fun makeSimpleCall() {
    server.enqueue(MockResponse(body = "healthy"))
    val callB = client.newCall(Request(server.url("/")))

      if (existingCall.host == host) return existingCall
    }
    return null
  }

  /**
   * Cancel all calls currently enqueued or executing. Includes calls executed both
   * [synchronously][Call.execute] and [asynchronously][Call.enqueue].
   */
  @Synchronized
  fun cancelAll() {
    for (call in readyAsyncCalls) {
      call.call.cancel()
    }
    for (call in runningAsyncCalls) {

    if (finalizableReferenceClass == null) {
      /*
       * FinalizableReference's class loader was reclaimed. While there's a chance that other
       * finalizable references could be enqueued subsequently (at which point the class loader
       * would be resurrected by virtue of us having a strong reference to it), we should pretty

    futureTasks.add(insertAt, task)

    // Impact the coordinator if we inserted at the front.
    return insertAt == 0
  }

  /**
   * Schedules immediate execution of [Task.tryCancel] on all currently-enqueued tasks. These calls
   * will not be made until any currently-executing task has completed. Tasks that return true will
   * be removed from the execution schedule.
   */
  fun cancelAll() {