A Kotlin coroutine showcase featuring two custom dispatchers

TwoCoroutineDispatchersTest.kt

package com.example

import kotlinx.coroutines.experimental.*
import kotlinx.coroutines.experimental.swing.Swing
import java.awt.BorderLayout
import java.awt.Dimension
import java.awt.Font
import java.io.IOException
import java.io.PrintWriter
import java.io.StringWriter
import java.nio.file.Files
import java.nio.file.Paths
import java.util.concurrent.ExecutorService
import java.util.concurrent.Executors
import javax.swing.JFrame
import javax.swing.JPanel
import javax.swing.JScrollPane
import javax.swing.JTextArea
import kotlin.concurrent.thread
import kotlin.coroutines.experimental.CoroutineContext

object IoDispatcher : CoroutineDispatcher() {
    private val ioExecutor: ExecutorService = Executors.newSingleThreadExecutor {
        thread(false, name = "I/O Queue", block = it::run)
    }

    override fun dispatch(context: CoroutineContext, block: Runnable) {
        ioExecutor.submit(block)
    }

    override fun toString() = "I/O Queue"
}

val Dispatchers.SingleThreadedIo: CoroutineDispatcher
    get() = IoDispatcher

@Throws(IOException::class)
suspend fun readFile(): String {
    return withContext(Dispatchers.SingleThreadedIo) {
        Files.newBufferedReader(Paths.get("/etc/passwd")).readText()
    }
}

fun main(vararg args: String) {
    GlobalScope.launch(Dispatchers.Swing) {
        val frame = JFrame().apply {
            defaultCloseOperation = JFrame.EXIT_ON_CLOSE
            preferredSize = Dimension(640, 480)
        }

        val textArea = JTextArea().apply {
            font = Font("Courier New", Font.PLAIN, 12)
        }

        val scrollPane = JScrollPane()
        scrollPane.viewport.add(textArea)

        val contentPane = frame.contentPane as JPanel
        contentPane.apply {
            layout = BorderLayout()
        }
        contentPane.add(scrollPane, BorderLayout.CENTER)

        frame.pack()
        frame.isVisible = true

        textArea.isEditable = false
        try {
            textArea.text = readFile()
        } catch (ioe: IOException) {
            textArea.text = StringWriter().also {
                ioe.printStackTrace(PrintWriter(it))
            }.buffer.toString()
        }
    }
}