fix BackpressureTimeout after checkpoint throw ShutdownException (#15)

* fix substream exception cause BackpressureTimeout

* update jdk to openjdk8

Author: CatTail

.travis.yml

@@ -4,7 +4,7 @@ scala:
 - 2.11.12
 - 2.12.7
 jdk:
-- oraclejdk8
+- openjdk8
 script:
 - sbt -J-XX:ReservedCodeCacheSize=128m ++$TRAVIS_SCALA_VERSION ";test:compile"
 # make 'git branch' work again

src/main/scala/aserralle/akka/stream/kcl/CommittableRecord.scala

@@ -5,6 +5,7 @@
 package aserralle.akka.stream.kcl
 
 import akka.Done
+import software.amazon.kinesis.exceptions.ShutdownException
 import software.amazon.kinesis.lifecycle.ShutdownReason
 import software.amazon.kinesis.processor.RecordProcessorCheckpointer
 import software.amazon.kinesis.retrieval.KinesisClientRecord
@@ -30,10 +31,16 @@ class CommittableRecord(
   def canBeCheckpointed(): Boolean =
     recordProcessorShutdownReason().isEmpty
 
-  def tryToCheckpoint(): Future[Done] =
+  def tryToCheckpoint(): Future[Boolean] =
     Future {
-      checkpointer.checkpoint(sequenceNumber, subSequenceNumber)
-      Done
+      try {
+        checkpointer.checkpoint(sequenceNumber, subSequenceNumber)
+        true
+      } catch {
+        case _: ShutdownException =>
+          false
+        case exception => throw exception
+      }
     }
 }
 

src/main/scala/aserralle/akka/stream/kcl/scaladsl/KinesisWorkerSource.scala

@@ -86,26 +86,23 @@ object KinesisWorkerSource {
 
         val `{` =
           b.add(scaladsl.Broadcast[immutable.Seq[CommittableRecord]](2))
-        val `}` = b.add(Zip[Done, immutable.Seq[CommittableRecord]])
+        val `}` = b.add(Zip[Boolean, immutable.Seq[CommittableRecord]])
         val `=` = b.add(Flow[KinesisClientRecord])
 
         `{`.out(0)
           .map(_.max)
-          .mapAsync(1)(r =>
-            if (r.canBeCheckpointed()) r.tryToCheckpoint()
-            else Future.successful(Done)) ~> `}`.in0
+          .mapAsync(1)(
+            r =>
+              if (r.canBeCheckpointed()) r.tryToCheckpoint()
+              else Future.successful(true)
+          ) ~> `}`.in0
         `{`.out(1) ~> `}`.in1
 
-        `}`.out.map(_._2).mapConcat(identity).map(_.record) ~> `=`
+        `}`.out.filter(_._1).map(_._2).mapConcat(identity).map(_.record) ~> `=`
 
         FlowShape(`{`.in, `=`.out)
       })
       .mergeSubstreams
-      .withAttributes(ActorAttributes.supervisionStrategy {
-        case _: ShutdownException =>
-          Resume
-        case _ => Stop
-      })
 
   def checkpointRecordsSink(
       settings: KinesisWorkerCheckpointSettings =