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Fix race in MapParallelOrderedObservable #906

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Merged
Avasil merged 1 commit into from
Jun 19, 2019
Merged

Fix race in MapParallelOrderedObservable #906

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28 changes: 22 additions & 6 deletions ...hared/src/main/scala/monix/reactive/internal/operators/MapParallelOrderedObservable.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,6 @@
package monix.reactive.internal.operators

import java.util.concurrent.ConcurrentLinkedQueue
import java.util.concurrent.locks.ReentrantLock

import monix.eval.Task
import monix.execution.Ack.{Continue, Stop}
Expand Down Expand Up @@ -81,16 +80,17 @@ private[reactive] final class MapParallelOrderedObservable[A, B](
// elements at the same time.
private[this] val queue = new ConcurrentLinkedQueue[CancelableFuture[B]]
// This lock makes sure that only one thread at the time sends processed elements downstream
// Note that we only use `tryLock()` - we never wait for acquiring lock
private[this] val sendDownstreamLock = new ReentrantLock()
private[this] val sendDownstreamSemaphore = AsyncSemaphore(1)

private def shouldStop: Boolean = isDone || lastAck == Stop

private def sendDownstreamOrdered(): Unit = {
// Only one thread should poll queue for completed tasks
// We can ignore it if there is one doing the work
if (sendDownstreamLock.tryLock()) {
val permit = sendDownstreamSemaphore.acquire()
composite += permit
def doSend(): Unit =
try {
composite -= permit
// Keep checking the head of a queue since we have to signal elements in order
while (!shouldStop && !queue.isEmpty && queue.peek().isCompleted) {
val head = queue.poll()
Expand Down Expand Up @@ -118,8 +118,24 @@ private[reactive] final class MapParallelOrderedObservable[A, B](
}
}
} finally {
sendDownstreamLock.unlock()
sendDownstreamSemaphore.release()
}
permit.value match {
case Some(Success(_)) =>
doSend()
case Some(Failure(error)) =>
lastAck = Stop
composite -= permit
self.onError(error)
case None =>
permit.onComplete {
case Success(_) =>
doSend()
case Failure(error) =>
lastAck = Stop
composite -= permit
self.onError(error)
}
}
}

Expand Down