CountDownLatch

1. CountDownLatch 代码示例

CountDownLatch 将代码的执行通过CountDownLatch#await的方法切成多块,以满足时序的要求

import java.util.concurrent.CountDownLatch

object Driver {
  val N: Int = 5

  def main(args: Array[String]): Unit = {
    val startSignal = new CountDownLatch(1)
    val doneSignal = new CountDownLatch(N)

    1.to(N).foreach{ id =>
      new Thread(new Worker(id, startSignal, doneSignal)).start()
    }

    startSignal.countDown()
    println("start:")
    doneSignal.await()
  }
}

class Worker(id: Int, startSignal: CountDownLatch, donwSignal: CountDownLatch) extends Runnable {
  override def run(): Unit = {
    try {
      startSignal.await()
      doWork()
      donwSignal.countDown()
    }
  }

  def doWork(): Unit = {
    println(s"work $id is running")
  }
}

2. scala实现类似的写法

object CountDownLatchDemo {
  import scala.concurrent.{Await, Future}
  import scala.concurrent.ExecutionContext.Implicits.global
  import scala.concurrent.duration._

  def main(args: Array[String]): Unit = {
    val n = 5
    val workerFutures = 1.to(n).map{ id =>
      Future{
        println(s"work $id is running")
      }
    }

    val driverFuture = Future.sequence(workerFutures)
    Await.result(driverFuture, 10.seconds)
    println("all done")
  }
}