monix.reactive.internal.operators.DoOnStartOperator.scala Maven / Gradle / Ivy
/*
* Copyright (c) 2014-2020 by The Monix Project Developers.
* See the project homepage at: https://monix.io
*
* 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 monix.reactive.internal.operators
import monix.eval.Task
import monix.execution.Ack
import monix.execution.Ack.Stop
import monix.reactive.Observable.Operator
import monix.reactive.observers.Subscriber
import scala.concurrent.Future
import scala.util.control.NonFatal
private[reactive] final class DoOnStartOperator[A](cb: A => Task[Unit]) extends Operator[A, A] {
def apply(out: Subscriber[A]): Subscriber[A] =
new Subscriber[A] {
implicit val scheduler = out.scheduler
private[this] var isDone = false
private[this] var isStart = true
def onNext(elem: A): Future[Ack] = {
if (isStart) {
// Protects calls to user code from within the operator and
// stream the error downstream if it happens, but if the
// error happens because of calls to `onNext` or other
// protocol calls, then the behavior should be undefined.
val t =
try {
cb(elem)
} catch {
case NonFatal(ex) => Task.raiseError(ex)
}
val ack = t
.redeemWith(
ex => Task.eval { onError(ex); Stop },
_ => Task.fromFuture(out.onNext(elem))
)
.runToFuture
isStart = false
ack.syncTryFlatten
} else {
out.onNext(elem)
}
}
def onError(ex: Throwable): Unit =
if (!isDone) {
isDone = true
out.onError(ex)
}
def onComplete(): Unit =
if (!isDone) {
isDone = true
out.onComplete()
}
}
}