Lab10

lab10/build.sbt

@@ -0,0 +1,18 @@
+name := "lab10"
+
+version := "0.1"
+
+scalaVersion := "2.12.11"
+
+libraryDependencies += "org.typelevel" %% "cats-core" % "2.0.0"
+libraryDependencies += "org.scalatest" %% "scalatest" % "3.1.1" % "test"
+
+libraryDependencies += "org.typelevel" %% "cats-effect" % "1.3.0" withSources() withJavadoc()
+
+scalacOptions ++= Seq(
+  "-feature",
+  "-deprecation",
+  "-unchecked",
+  "-language:postfixOps",
+  "-language:higherKinds",
+  "-Ypartial-unification")

lab10/project/build.properties

@@ -0,0 +1 @@
+sbt.version = 1.3.10

lab10/src/main/scala/Main.scala

@@ -0,0 +1,36 @@
+import cats.effect.{ExitCode, IO, IOApp, Resource}
+import cats.effect.concurrent.MVar
+import cats.syntax.all._
+
+import scala.concurrent.duration._
+
+object Main extends IOApp {
+  def runPrinter(mvar: MVar[IO, String]): Resource[IO, Unit] = {
+    def rec: IO[Unit] = for {
+      value <- mvar.take
+      _ <- IO(println(value))
+      _ <- rec
+    } yield ()
+
+    Resource.make(rec.start)(_.cancel.flatMap(_ => IO(println("printer is closed")))).void
+  }
+
+  def runCounter(mvar: MVar[IO, String]): Resource[IO, Unit] = {
+    def rec(counter: Long): IO[Unit] = for {
+      _ <- IO.sleep(1.seconds)
+      _ <- mvar.put(counter.toString)
+      _ <- rec(counter + 1)
+    } yield ()
+
+    Resource.make(rec(0).start)(_.cancel.flatMap(_ => IO(println("counter is closed")))).void
+  }
+
+  val gracefulShutdownProgram: Resource[IO, Unit] = for {
+    mvar <- Resource.make(MVar.empty[IO, String])(_ => IO(print("release")))
+    _ <- runCounter(mvar)
+    _ <- runPrinter(mvar)
+  } yield ()
+
+  override def run(args: List[String]): IO[ExitCode] =
+    gracefulShutdownProgram.use(_ => IO.never)
+}