flink 并行度导致输出控制台结果问题

Question

我的电脑是8线程，当我运行下面这段代码时，可以输出结果，但是当把并行度注释掉时，就不输出结果了，这是为什么呢？输入数据一样，watermark应该都是一样的啊

输入数据为：
1585721697000,xiao,8
1585721700000,xiao,10
1585721705000,xiao,4
1585721715000,xiao,9

case class Student(id:Long,name:String,age:Int)
object test3 {
  def main(args: Array[String]): Unit = {
    val env = StreamExecutionEnvironment.getExecutionEnvironment
    env.setParallelism(4)
    //指定时间类型
    env.setStreamTimeCharacteristic(TimeCharacteristic.EventTime)

    val value: DataStream[String] = env.socketTextStream("localhost", 9999)

    val map: DataStream[Student] = value.map(line => {
      val arr: Array[String] = line.split(",")
      Student(arr(0).toLong, arr(1), arr(2).toInt)
    })
    val value1: DataStream[Student] = map.assignTimestampsAndWatermarks(new BoundedOutOfOrdernessTimestampExtractor[Student](Time.seconds(3)) {
      override def extractTimestamp(t: Student): Long = {
        t.id
      }
    })
    val value2: KeyedStream[Student, String] = value1.keyBy(_.name)
    val value3: WindowedStream[Student, String, TimeWindow] = value2.timeWindow(Time.seconds(10))
    val value4: DataStream[Student] = value3.sum(2)
    value4.print()
    env.execute()
  }
}