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IOApp.scala
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IOApp.scala
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/*
* Copyright 2020 Typelevel
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package cats.effect
import java.util.concurrent.CountDownLatch
trait IOApp {
def run(args: List[String]): IO[ExitCode]
protected val runtime: unsafe.IORuntime = unsafe.IORuntime.global
final def main(args: Array[String]): Unit = {
val rt = Runtime.getRuntime()
val latch = new CountDownLatch(1)
@volatile var error: Throwable = null
@volatile var result: ExitCode = null
val ioa = run(args.toList)
val fiber =
ioa
.onCancel(IO {
error = new RuntimeException("IOApp main fiber canceled")
latch.countDown()
})
.unsafeRunFiber(
{ t =>
error = t
latch.countDown()
},
{ a =>
result = a
latch.countDown()
})(runtime)
def handleShutdown(): Unit = {
if (latch.getCount() > 0) {
val cancelLatch = new CountDownLatch(1)
fiber.cancel.unsafeRunAsync(_ => cancelLatch.countDown())(runtime)
cancelLatch.await()
}
// Clean up after ourselves, relevant for running IOApps in sbt,
// otherwise scheduler threads will accumulate over time.
runtime.internalShutdown()
runtime.shutdown()
}
val hook = new Thread(() => handleShutdown())
hook.setName("io-cancel-hook")
rt.addShutdownHook(hook)
try {
latch.await()
if (error != null) {
// Runtime has already been shutdown in IOFiber.
throw error
} else {
// Clean up after ourselves, relevant for running IOApps in sbt,
// otherwise scheduler threads will accumulate over time.
runtime.internalShutdown()
runtime.shutdown()
System.exit(result.code)
}
} catch {
// this handles sbt when fork := false
case _: InterruptedException =>
hook.start()
rt.removeShutdownHook(hook)
Thread.currentThread().interrupt()
}
}
}
object IOApp {
trait Simple extends IOApp {
def run: IO[Unit]
final def run(args: List[String]): IO[ExitCode] = run.as(ExitCode.Success)
}
}