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Sub-module of Monix, exposing the Observable pattern for modeling of reactive streams. See: https://monix.io
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/*
* Copyright (c) 2014-2021 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 java.util.concurrent.TimeUnit
import monix.execution.Ack.{Continue, Stop}
import monix.execution.cancelables.{CompositeCancelable, MultiAssignCancelable, SingleAssignCancelable}
import monix.execution.{Ack, Cancelable}
import monix.reactive.Observable
import monix.reactive.observers.Subscriber
import scala.concurrent.Future
import scala.concurrent.duration.{FiniteDuration, MILLISECONDS}
import scala.util.Success
private[reactive] final class EchoObservable[+A](source: Observable[A], timeout: FiniteDuration, onlyOnce: Boolean)
extends Observable[A] {
private[this] val timeoutMillis = timeout.toMillis
def unsafeSubscribeFn(out: Subscriber[A]): Cancelable = {
val task = MultiAssignCancelable()
val mainTask = SingleAssignCancelable()
val composite = CompositeCancelable(mainTask, task)
mainTask := source.unsafeSubscribeFn(new Subscriber[A] with Runnable { self =>
implicit val scheduler = out.scheduler
private[this] var ack: Future[Ack] = Continue
private[this] var lastEvent: A = _
private[this] var lastTSInMillis: Long = 0L
private[this] var isDone = false
private[this] var hasValue = false
locally {
scheduleNext(timeoutMillis)
}
def scheduleNext(delayMillis: Long): Unit = {
// No need to synchronize this assignment, since we have a
// happens-before relationship between scheduleOnce invocations.
task := scheduler.scheduleOnce(delayMillis, TimeUnit.MILLISECONDS, self)
()
}
def run(): Unit = {
def cancelMainTask() =
self.synchronized {
isDone = true
mainTask.cancel()
Stop
}
self.synchronized {
if (isDone)
() // do nothing else
else if (!ack.isCompleted) {
// The consumer is still processing its last message,
// and this processing time does not enter the picture.
// Given that the lastTSInMillis is set after Continue
// happens, it means that we'll wait for Continue plus
// our period in order to get another chance to emit
ack.onComplete {
case Success(Continue) =>
scheduleNext(timeoutMillis)
case _ =>
()
}
} else if (lastEvent == null || !hasValue) {
// on this branch either the data source hasn't emitted anything
// yet (lastEvent == null), or we don't have a new value since
// the last time we've tried (!hasValue), so keep waiting
scheduleNext(timeoutMillis)
} else {
val rightNow = scheduler.clockMonotonic(MILLISECONDS)
val sinceLastOnNext = rightNow - lastTSInMillis
if (sinceLastOnNext >= timeoutMillis) {
// hasValue is set to false only if the onlyOnce param is
// set to true (otherwise we keep repeating our current
// value until a new one happens)
hasValue = !onlyOnce
// this call is actually synchronous because we're testing
// for ack.isCompleted above, but doing it nonetheless because
// of safety and because last ack might have been a Stop
ack = ack.syncTryFlatten.syncFlatMap {
case Continue =>
out.onNext(lastEvent).syncFlatMap {
case Continue =>
// the speed with which the downstream replied with Continue
// matters in this case, so we are measuring it and
// subtracting it from the period
val executionTime = scheduler.clockMonotonic(MILLISECONDS) - rightNow
val delay =
if (timeoutMillis > executionTime)
timeoutMillis - executionTime
else 0L
scheduleNext(delay)
Continue
case Stop =>
cancelMainTask()
}
case Stop =>
cancelMainTask()
}
} else {
val remainingTime = timeoutMillis - sinceLastOnNext
scheduleNext(remainingTime)
}
}
}
}
def onNext(elem: A): Future[Ack] = {
def unfreeze(): Ack = {
hasValue = true
lastTSInMillis = scheduler.clockMonotonic(MILLISECONDS)
Continue
}
// Handling flattening manually to avoid
// extra synchronization for synchronous onNext
def signalNext(ack: Future[Ack]): Future[Ack] =
ack match {
case Continue =>
if (isDone) Stop
else
out.onNext(elem) match {
case Continue => unfreeze()
case Stop => Stop
case async =>
async.flatMap {
case Continue => self.synchronized(unfreeze())
case Stop => Stop
}
}
case Stop => Stop
case async =>
async.flatMap(signalNext)
}
self.synchronized {
if (isDone) Stop
else {
lastEvent = elem
ack = signalNext(ack.syncTryFlatten)
ack
}
}
}
def onError(ex: Throwable): Unit =
self.synchronized {
if (!isDone) {
isDone = true
task.cancel()
out.onError(ex)
}
}
def onComplete(): Unit = {
def signal(): Ack = {
if (!isDone) {
isDone = true
task.cancel()
out.onComplete()
}
Stop
}
self.synchronized {
ack = ack.syncTryFlatten match {
case Stop => Stop
case Continue => signal()
case async =>
async.flatMap {
case Continue => self.synchronized(signal())
case Stop => Stop
}
}
}
}
})
composite
}
}