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Examples of Quasar in Kotlin (eugenp#7045)
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‎kotlin-quasar/pom.xml‎

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>com.baeldung</groupId>
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<artifactId>kotlin-quasar</artifactId>
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<version>1.0.0-SNAPSHOT</version>
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<name>kotlin-quasar</name>
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<packaging>jar</packaging>
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<dependencies>
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<dependency>
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<groupId>org.jetbrains.kotlin</groupId>
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<artifactId>kotlin-stdlib-jdk8</artifactId>
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<version>${kotlin.version}</version>
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</dependency>
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<dependency>
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<groupId>org.jetbrains.kotlin</groupId>
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<artifactId>kotlin-test</artifactId>
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<version>${kotlin.version}</version>
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<scope>test</scope>
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</dependency>
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<dependency>
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<groupId>co.paralleluniverse</groupId>
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<artifactId>quasar-core</artifactId>
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<version>${quasar.version}</version>
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</dependency>
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<dependency>
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<groupId>co.paralleluniverse</groupId>
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<artifactId>quasar-actors</artifactId>
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<version>${quasar.version}</version>
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</dependency>
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<dependency>
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<groupId>co.paralleluniverse</groupId>
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<artifactId>quasar-reactive-streams</artifactId>
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<version>${quasar.version}</version>
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</dependency>
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<dependency>
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<groupId>co.paralleluniverse</groupId>
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<artifactId>quasar-kotlin</artifactId>
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<version>${quasar.version}</version>
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</dependency>
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<dependency>
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<groupId>junit</groupId>
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<artifactId>junit</artifactId>
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<version>4.12</version>
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</dependency>
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</dependencies>
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<build>
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<sourceDirectory>src/main/kotlin</sourceDirectory>
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<testSourceDirectory>src/test/kotlin</testSourceDirectory>
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<plugins>
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<plugin>
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<groupId>org.jetbrains.kotlin</groupId>
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<artifactId>kotlin-maven-plugin</artifactId>
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<version>${kotlin.version}</version>
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<executions>
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<execution>
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<id>compile</id>
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<phase>compile</phase>
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<goals>
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<goal>compile</goal>
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</goals>
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</execution>
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<execution>
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<id>test-compile</id>
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<phase>test-compile</phase>
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<goals>
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<goal>test-compile</goal>
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</goals>
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</execution>
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</executions>
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<configuration>
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<jvmTarget>1.8</jvmTarget>
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</configuration>
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</plugin>
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<plugin>
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<artifactId>maven-dependency-plugin</artifactId>
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<version>3.1.1</version>
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<executions>
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<execution>
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<id>getClasspathFilenames</id>
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<goals>
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<goal>properties</goal>
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</goals>
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</execution>
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</executions>
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</plugin>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-surefire-plugin</artifactId>
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<version>2.22.1</version>
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<configuration>
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<argLine>-Dco.paralleluniverse.fibers.verifyInstrumentation=true</argLine>
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<argLine>-javaagent:${co.paralleluniverse:quasar-core:jar}</argLine>
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</configuration>
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</plugin>
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<plugin>
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<groupId>org.codehaus.mojo</groupId>
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<artifactId>exec-maven-plugin</artifactId>
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<version>1.3.2</version>
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<configuration>
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<workingDirectory>target/classes</workingDirectory>
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<executable>echo</executable>
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<arguments>
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<argument>-javaagent:${co.paralleluniverse:quasar-core:jar}</argument>
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<argument>-classpath</argument> <classpath/>
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<argument>com.baeldung.quasar.QuasarHelloWorldKt</argument>
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</arguments>
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</configuration>
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</plugin>
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</plugins>
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</build>
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<properties>
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<quasar.version>0.8.0</quasar.version>
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<kotlin.version>1.3.31</kotlin.version>
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</properties>
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</project>

‎kotlin-quasar/src/main/kotlin/com/baeldung/quasar/QuasarHelloWorld.kt‎

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package com.baeldung.quasar
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import co.paralleluniverse.fibers.Fiber
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import co.paralleluniverse.strands.SuspendableRunnable
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/**
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* Entrypoint into the application
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*/
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fun main(args: Array<String>) {
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class Runnable : SuspendableRunnable {
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override fun run() {
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println("Hello")
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}
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}
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val result = Fiber<Void>(Runnable()).start()
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result.join()
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println("World")
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}

‎kotlin-quasar/src/test/kotlin/com/baeldung/quasar/ChannelsTest.kt‎

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package com.baeldung.quasar
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import co.paralleluniverse.fibers.Suspendable
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import co.paralleluniverse.kotlin.fiber
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import co.paralleluniverse.strands.channels.Channels
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import co.paralleluniverse.strands.channels.Selector
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import com.google.common.base.Function
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import org.junit.Test
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class ChannelsTest {
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@Test
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fun createChannel() {
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Channels.newChannel<String>(0, // The size of the channel buffer
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Channels.OverflowPolicy.BLOCK, // The policy for when the buffer is full
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true, // Whether we should optimize for a single message producer
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true) // Whether we should optimize for a single message consumer
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}
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@Test
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fun blockOnMessage() {
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val channel = Channels.newChannel<String>(0, Channels.OverflowPolicy.BLOCK, true, true)
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fiber @Suspendable {
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while (!channel.isClosed) {
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val message = channel.receive()
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println("Received: $message")
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}
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println("Stopped receiving messages")
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}
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channel.send("Hello")
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channel.send("World")
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channel.close()
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}
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@Test
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fun selectReceiveChannels() {
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val channel1 = Channels.newChannel<String>(0, Channels.OverflowPolicy.BLOCK, true, true)
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val channel2 = Channels.newChannel<String>(0, Channels.OverflowPolicy.BLOCK, true, true)
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fiber @Suspendable {
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while (!channel1.isClosed && !channel2.isClosed) {
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val received = Selector.select(Selector.receive(channel1), Selector.receive(channel2))
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println("Received: $received")
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}
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}
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fiber @Suspendable {
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for (i in 0..10) {
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channel1.send("Channel 1: $i")
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}
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}
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fiber @Suspendable {
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for (i in 0..10) {
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channel2.send("Channel 2: $i")
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}
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}
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}
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@Test
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fun selectSendChannels() {
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val channel1 = Channels.newChannel<String>(0, Channels.OverflowPolicy.BLOCK, true, true)
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val channel2 = Channels.newChannel<String>(0, Channels.OverflowPolicy.BLOCK, true, true)
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fiber @Suspendable {
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for (i in 0..10) {
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Selector.select(
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Selector.send(channel1, "Channel 1: $i"),
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Selector.send(channel2, "Channel 2: $i")
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)
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}
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}
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fiber @Suspendable {
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while (!channel1.isClosed) {
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val msg = channel1.receive()
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println("Read: $msg")
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}
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}
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fiber @Suspendable {
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while (!channel2.isClosed) {
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val msg = channel2.receive()
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println("Read: $msg")
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}
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}
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}
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@Test
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fun tickerChannel() {
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val channel = Channels.newChannel<String>(3, Channels.OverflowPolicy.DISPLACE)
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for (i in 0..10) {
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val tickerConsumer = Channels.newTickerConsumerFor(channel)
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fiber @Suspendable {
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while (!tickerConsumer.isClosed) {
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val message = tickerConsumer.receive()
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println("Received on $i: $message")
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}
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println("Stopped receiving messages on $i")
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}
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}
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for (i in 0..50) {
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channel.send("Message $i")
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}
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channel.close()
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}
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@Test
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fun transformOnSend() {
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val channel = Channels.newChannel<String>(0, Channels.OverflowPolicy.BLOCK, true, true)
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fiber @Suspendable {
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while (!channel.isClosed) {
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val message = channel.receive()
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println("Received: $message")
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}
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println("Stopped receiving messages")
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}
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val transformOnSend = Channels.mapSend(channel, Function<String, String> { msg: String? -> msg?.toUpperCase() })
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transformOnSend.send("Hello")
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transformOnSend.send("World")
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channel.close()
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}
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@Test
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fun transformOnReceive() {
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val channel = Channels.newChannel<String>(0, Channels.OverflowPolicy.BLOCK, true, true)
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val transformOnReceive = Channels.map(channel, Function<String, String> { msg: String? -> msg?.reversed() })
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fiber @Suspendable {
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while (!transformOnReceive.isClosed) {
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val message = transformOnReceive.receive()
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println("Received: $message")
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}
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println("Stopped receiving messages")
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}
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channel.send("Hello")
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channel.send("World")
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channel.close()
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}
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}

‎kotlin-quasar/src/test/kotlin/com/baeldung/quasar/DataflowTest.kt‎

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package com.baeldung.quasar
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import co.paralleluniverse.strands.dataflow.Val
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import co.paralleluniverse.strands.dataflow.Var
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import org.junit.Assert
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import org.junit.Test
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import java.util.concurrent.TimeUnit
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class DataflowTest {
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@Test
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fun testValVar() {
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val a = Var<Int>()
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val b = Val<Int>()
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val c = Var<Int> { a.get() + b.get() }
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val d = Var<Int> { a.get() * b.get() }
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// (a*b) - (a+b)
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val initialResult = Val<Int> { d.get() - c.get() }
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val currentResult = Var<Int> { d.get() - c.get() }
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a.set(2)
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b.set(4)
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Assert.assertEquals(2, initialResult.get())
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Assert.assertEquals(2, currentResult.get())
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a.set(3)
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TimeUnit.SECONDS.sleep(1)
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Assert.assertEquals(2, initialResult.get())
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Assert.assertEquals(5, currentResult.get())
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}
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}

‎kotlin-quasar/src/test/kotlin/com/baeldung/quasar/PiAsyncTest.kt‎

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package com.baeldung.quasar
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import co.paralleluniverse.fibers.Fiber
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import co.paralleluniverse.fibers.FiberAsync
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import co.paralleluniverse.fibers.Suspendable
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import co.paralleluniverse.kotlin.fiber
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import co.paralleluniverse.strands.Strand
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import org.junit.Assert
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import org.junit.Test
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import java.math.BigDecimal
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import java.util.concurrent.TimeUnit
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interface PiCallback {
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fun success(result: BigDecimal)
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fun failure(error: Exception)
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}
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fun computePi(callback: PiCallback) {
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println("Starting calculations")
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TimeUnit.SECONDS.sleep(2)
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println("Finished calculations")
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callback.success(BigDecimal("3.14"))
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}
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class PiAsync : PiCallback, FiberAsync<BigDecimal, Exception>() {
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override fun success(result: BigDecimal) {
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asyncCompleted(result)
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}
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override fun failure(error: Exception) {
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asyncFailed(error)
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}
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override fun requestAsync() {
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computePi(this)
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}
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}
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class PiAsyncTest {
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@Test
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fun testPi() {
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val result = fiber @Suspendable {
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val pi = PiAsync()
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println("Waiting to get PI on: " + Fiber.currentFiber().name)
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val result = pi.run()
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println("Got PI")
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result
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}.get()
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Assert.assertEquals(BigDecimal("3.14"), result)
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}
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}

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