在documentation to implement a KillSwitch
之后,我能够编写这个简单的例子来阻止Source发出无限数字。
object KillSwitchSample extends App {
implicit val actorSystem = ActorSystem()
implicit val materializer = ActorMaterializer()
val sourceGraph: Graph[SourceShape[Int], NotUsed] = new NumbersSource
val mySource: Source[Int, NotUsed] = Source.fromGraph(sourceGraph)
val killSwitch = KillSwitches.shared("switch")
RunnableGraph.fromGraph(GraphDSL.create() { implicit builder =>
import GraphDSL.Implicits._
val flow = builder.add(Flow[Int].map(_ * 2))
mySource.via(killSwitch.flow) ~> flow ~> Sink.foreach(println)
ClosedShape
}).run()
Thread.sleep(200)
killSwitch.shutdown()
}
class NumbersSource extends GraphStage[SourceShape[Int]] {
val out: Outlet[Int] = Outlet("NumbersSource")
override val shape: SourceShape[Int] = SourceShape(out)
override def createLogic(inheritedAttributes: Attributes): GraphStageLogic =
new GraphStageLogic(shape) {
private var counter = 1
setHandler(out, new OutHandler {
override def onPull(): Unit = {
push(out, counter)
counter += 1
}
})
}
}
我的用例不同,因为Source使用OpenCV从视频文件中发出帧。为什么上游没有被取消?我在这里缺少什么?
object KillSwitchMinimalMain extends App {
val libopencv_java = new File("lib").listFiles().map(_.getAbsolutePath).filter(_.contains("libopencv_java"))
System.load(libopencv_java(0))
implicit val actorSystem = ActorSystem()
implicit val materializer = ActorMaterializer()
val videoFile = Video("Video.MOV")
val sourceGraph: Graph[SourceShape[Frame], NotUsed] = new VideoSource(videoFile)
val videoSource: Source[Frame, NotUsed] = Source.fromGraph(sourceGraph)
val killSwitch = KillSwitches.shared("switch")
RunnableGraph.fromGraph(GraphDSL.create() { implicit builder =>
import GraphDSL.Implicits._
val matConversion: FlowShape[Frame, Image] = builder.add(Flow[Frame].map { el => MediaConversion.convertMatToImage(el.frame) })
videoSource.via(killSwitch.flow) ~> matConversion ~> Sink.foreach(println)
ClosedShape
}).run()
Thread.sleep(200)
killSwitch.shutdown()
}
class VideoSource(videoFile: Video) extends GraphStage[SourceShape[Frame]] {
val out: Outlet[Frame] = Outlet("VideoSource")
override val shape: SourceShape[Frame] = SourceShape(out)
val log: Logger = LoggerFactory.getLogger(getClass)
override def createLogic(inheritedAttributes: Attributes): GraphStageLogic =
new GraphStageLogic(shape) {
private val capture = new VideoCapture()
private val frame = new Mat()
private var videoPos: Double = _
override def preStart(): Unit = {
capture.open(videoFile.filepath)
readFrame()
}
setHandler(out, new OutHandler {
override def onPull(): Unit = {
push(out, Frame(videoPos, frame))
readFrame()
}
})
private def readFrame(): Unit = {
if (capture.isOpened) {
videoPos = capture.get(1)
log.info(s"reading frame $videoPos")
capture.read(frame)
}
}
}
}
@svezfaz提出的控制台输出:
13:17:00.046 [default-akka.actor.default-dispatcher-3] INFO de.itd.video.VideoSource - reading frame 0.0
13:17:00.160 [default-akka.actor.default-dispatcher-3] INFO de.itd.video.VideoSource - reading frame 1.0
javafx.scene.image.WritableImage@64b06f30
13:17:00.698 [default-akka.actor.default-dispatcher-3] INFO de.itd.video.VideoSource - reading frame 2.0
javafx.scene.image.WritableImage@1e011979
13:17:00.826 [default-akka.actor.default-dispatcher-3] INFO de.itd.video.VideoSource - reading frame 3.0
javafx.scene.image.WritableImage@52c9a35c
13:17:00.969 [default-akka.actor.default-dispatcher-3] INFO de.itd.video.VideoSource - reading frame 4.0
javafx.scene.image.WritableImage@13968f9e
13:17:01.137 [default-akka.actor.default-dispatcher-3] INFO de.itd.video.VideoSource - reading frame 5.0
javafx.scene.image.WritableImage@6ab783be
// and so on ..
答案 0 :(得分:1)
问题是您在自定义阶段引入了阻止。我不了解OpenCV API,但我猜你在调用capture.read(frame)
时会发生这种情况。
现在,除非另有说明,否则您的图表将在一个Actor中运行,因此在您的阶段中阻塞将阻止整个actor。
在源代码后强制async
边界应该可以解决问题。
另请注意,此处您不需要GraphDSL,所有内容都可以使用via / to DSL紧凑运行。
以下的解决方案尝试
object KillSwitchMinimalMain extends App {
val libopencv_java = new File("lib").listFiles().map(_.getAbsolutePath).filter(_.contains("libopencv_java"))
System.load(libopencv_java(0))
implicit val actorSystem = ActorSystem()
implicit val materializer = ActorMaterializer()
val videoFile = Video("Video.MOV")
val killSwitch = KillSwitches.shared("switch")
val matConversion = Flow[ByteString].map { _.utf8String }
Source.fromGraph(new VideoSource())
.async
.via(killSwitch.flow)
.via(matConversion)
.runForeach(println)
Thread.sleep(200)
killSwitch.shutdown()
}
有关Akka Streams底层并发模型的更多信息,请阅读此blogpost。