scala-cats IOApp应该如何获取ExecutionContext

Question

我最近将我的应用程序转换为继承cats的IOApp，如下所述。我在文件中读到：

IOApp已经提供了Timer[IO]依赖项，因此JVM不再需要隐式ExecutionContext在范围内

但是，我正在与其他几个确实需要ExecutionContext的库(即http4s(进行交互。在这种类型的应用程序中，有推荐的获取方法吗？好的旧import scala.concurrent.ExecutionContext.Implicits.global和提供的Timer[IO]玩得好吗？

Answer 1

尝试扩展特性IOApp.WithContext。对于全局ExecutionContext

import cats.effect._
import scala.concurrent.ExecutionContext
object Main extends IOApp.WithContext {
implicit val ec = ExecutionContext.global
override protected def executionContextResource: Resource[SyncIO, ExecutionContext] =
Resource.liftF(SyncIO(ec))
def run(args: List[String]): IO[ExitCode] = {
implicitly[Timer[IO]]
implicitly[ContextShift[IO]]
implicitly[ExecutionContext]
IO.pure(ExitCode.Success)
}
}

或者对于来自具有固定线程数的线程池的CCD_ 7

import java.util.concurrent.{Executors, TimeUnit}
import cats.effect._
import scala.concurrent.ExecutionContext
object Main extends IOApp.WithContext {
override protected def executionContextResource: Resource[SyncIO, ExecutionContext] =
Resource.make(SyncIO(Executors.newFixedThreadPool(8)))(pool => SyncIO {
pool.shutdown()
pool.awaitTermination(10, TimeUnit.SECONDS)
}).map(ExecutionContext.fromExecutorService)
def run(args: List[String]): IO[ExitCode] = {
executionContextResource.use { implicit ec =>
implicitly[Timer[IO]]
implicitly[ContextShift[IO]]
implicitly[ExecutionContext]
SyncIO.pure(ExitCode.Success)
}.toIO
}
}

https://github.com/typelevel/cats-effect/issues/337

https://github.com/typelevel/cats-effect/pull/344