monifu.reactive.internals.FreezeOnFirstOnNextSubscriber.scala Maven / Gradle / Ivy

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/*
 * Copyright (c) 2014-2016 by its authors. Some rights reserved.
 * 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 monifu.reactive.internals

import monifu.concurrent.atomic.padded.Atomic
import monifu.reactive.{Ack, Subscriber}
import scala.concurrent.{Future, Promise}


private[reactive] final class FreezeOnFirstOnNextSubscriber[-T]
  (underlying: Subscriber[T])
  extends Subscriber[T] { self =>

  implicit val scheduler = underlying.scheduler

  private[this] val isConnected = Atomic(false)
  private[this] val connectedPromise = Promise[Ack]()
  private[this] val firstTimePromise = Promise[Unit]()

  def initializeOnNext(ack: => Future[Ack]): Unit = {
    firstTimePromise.future.onComplete { _ =>
      connectedPromise.tryCompleteWith(ack)
      isConnected set true
    }
  }

  def onNext(elem: T): Future[Ack] = {
    if (!isConnected.get) {
      firstTimePromise.trySuccess(())
      connectedPromise.future
    }
    else {
      // fast path
      underlying.onNext(elem)
    }
  }

  def onComplete() = {
    if (!isConnected.get) firstTimePromise.trySuccess(())
    // we cannot take a fast path here
    connectedPromise.future.onContinueSignalComplete(underlying)
  }

  def onError(ex: Throwable) = {
    if (!isConnected.get) firstTimePromise.trySuccess(())
    // we cannot take a fast path here
    connectedPromise.future.onContinueSignalError(underlying, ex)
  }
}