redQueue.execute("task") {
      log += "run@${taskFaker.nanoTime}"
    }

    val idleLatch1 = redQueue.idleLatch()
    val idleLatch2 = redQueue.idleLatch()
    assertThat(idleLatch2).isSameAs(idleLatch1)
  }

  private val Int.µs: Long
    get() = this * 1_000L

    queue.schedule("task") {
      Thread.sleep(250)
      backend.shutdown()
      return@schedule -1L
    }

    assertThat(queue.idleLatch().await(500L, TimeUnit.MILLISECONDS)).isTrue()
    assertThat(queue.idleLatch().count).isEqualTo(0)
  }

          block()
          return -1L
        }
      },
      delayNanos,
    )
  }

  /** Returns a latch that reaches 0 when the queue is next idle. */
  fun idleLatch(): CountDownLatch {
    taskRunner.lock.withLock {
      // If the queue is already idle, that's easy.
      if (activeTask == null && futureTasks.isEmpty()) {
        return CountDownLatch(0)
      }

      // We wait at most 1 second, so we don't ever turn multiple lost threads into
      // a test timeout failure.
      val waitTime = (entryTime + 1_000_000_000L - System.nanoTime())
      if (!queue.idleLatch().await(waitTime, TimeUnit.NANOSECONDS)) {
        TaskRunner.INSTANCE.lock.withLock {
          TaskRunner.INSTANCE.cancelAll()
        }
        fail<Unit>("Queue still active after 1000 ms")
      }
    }

    streamsToClose?.closeQuietly()
  }

  /** For testing: force this web socket to release its threads. */
  @Throws(InterruptedException::class)
  fun tearDown() {
    taskQueue.shutdown()
    taskQueue.idleLatch().await(10, TimeUnit.SECONDS)
  }

  @Synchronized fun sentPingCount(): Int = sentPingCount

  @Synchronized fun receivedPingCount(): Int = receivedPingCount

    // Cause acceptConnections() to break out.
    serverSocket.close()

    // Await shutdown.
    for (queue in taskRunner.activeQueues()) {
      if (!queue.idleLatch().await(5, TimeUnit.SECONDS)) {
        throw IOException("Gave up waiting for queue to shut down")
      }
    }
    taskRunnerBackend.shutdown()
  }

  private fun serveConnection(raw: Socket) {