/** Used by [AsyncCall.run] to signal completion. */
  internal fun finished(call: AsyncCall) {
    promoteAndExecute(finishedAsyncCall = call)
  }

  /** Used by [Call.execute] to signal completion. */
  internal fun finished(call: RealCall) {
    promoteAndExecute(finishedCall = call)
  }

  /** Returns a snapshot of the calls currently awaiting execution. */
  @Synchronized