如何终止从Shell启动的FS2流？

Question

如果我从SBT shell运行这个程序，然后取消它，它将继续打印"hello“。我得离开SBT让它停下来。为什么会这样呢？

import cats.effect.{ExitCode, IO, IOApp}
import fs2.Stream
import scala.concurrent.duration._

object FS2 extends IOApp {

  override def run(args: List[String]) = 
      Stream.awakeEvery[IO](5.seconds).map { _ =>
        println("hello")
      }.compile.drain.as(ExitCode.Error)
}

Answer 1

正如注释中已经提到的，您的应用程序运行在另一个线程中，并且它永远不会终止，因为流是无限的，所以当应用程序接收到像SIGTERM或SIGINT这样的信号时，您必须手动终止它(每当您点击ctrl+c终止应用程序时，它就发出)。

你可以这样做：

1. 创建递延
2. 的实例，在接收到任何术语或INT信号后，使用它触发interruptWhen。

例如：

import sun.misc.Signal

object FS2 extends IOApp {

  override def run(args: List[String]): IO[ExitCode] = for {
    cancel <- Deferred[IO, Either[Throwable, Unit]] //deferred used as flat telling if terminations signal
                                                    //was received
    _ <- (IO.async_[Unit]{ cb =>
      Signal.handle(
        new Signal("INT"), //INT and TERM signals are nearly identical, we have to handle both
        (sig: Signal) => cb(Right(()))
      )
      Signal.handle(
        new Signal("TERM"),
        (sig: Signal) => cb(Right(()))
      )
    } *> cancel.complete(Right(()))).start //after INT or TERM signal is intercepted it will complete
                                           //deferred and terminate fiber
                                           //we have to run method start to run waiting for signal in another fiber
                                           //in other case program will block here
    app <- Stream.awakeEvery[IO](1.seconds).map { _ => //your stream
      println("hello")
    }.interruptWhen(cancel).compile.drain.as(ExitCode.Error)  //interruptWhen ends stream when deferred completes
  } yield app

}

当您在shell中单击ctrl + c时，此版本的应用程序将终止。