action(stream)
          }
        }
      }
      return@FutureTask null
    }
  }

  /** Returns once all stream actions complete successfully. */
  fun awaitSuccess() {
    val futureTask =
      results.poll(5, TimeUnit.SECONDS)
        ?: throw AssertionError("no onRequest call received")
    futureTask.get(5, TimeUnit.SECONDS)
  }