Third try at concurrency

src/main/kotlin/mdnet/base/MangaDexClient.kt

@@ -28,7 +28,9 @@ import com.fasterxml.jackson.module.kotlin.readValue
 import java.io.File
 import java.io.FileReader
 import java.io.IOException
+import java.util.concurrent.CountDownLatch
 import java.util.concurrent.Executors
+import java.util.concurrent.ScheduledFuture
 import java.util.concurrent.TimeUnit
 import java.util.regex.Pattern
 import mdnet.base.Main.dieWithError
@@ -46,6 +48,7 @@ class ClientSettingsException(message: String) : Exception(message)
 class MangaDexClient(private val settingsFile: File, databaseFile: File, cacheFolder: File) {
     // this must remain single-threaded because of how the state mechanism works
     private val executor = Executors.newSingleThreadScheduledExecutor()
+    private lateinit var scheduledFuture: ScheduledFuture<*>
 
     private val database: Database
     private val cache: DiskLruCache
@@ -89,7 +92,7 @@ class MangaDexClient(private val settingsFile: File, databaseFile: File, cacheFo
     fun runLoop() {
         LOGGER.info { "Mangadex@Home Client initialized - starting normal operation." }
 
-        executor.scheduleWithFixedDelay({
+        scheduledFuture = executor.scheduleWithFixedDelay({
             try {
                 // this blocks the executor, so no worries about concurrency
                 reloadClientSettings()
@@ -145,22 +148,31 @@ class MangaDexClient(private val settingsFile: File, databaseFile: File, cacheFo
     }
 
     fun shutdown() {
+        LOGGER.info { "Mangadex@Home Client shutting down" }
+        val latch = CountDownLatch(1)
+
+        scheduledFuture.cancel(false)
+
         executor.schedule({
-            LOGGER.info { "Mangadex@Home Client shutting down" }
             if (webUi != null) {
                 stopWebUi()
             }
             if (imageServer != null) {
                 stopImageServer()
             }
-            LOGGER.info { "Mangadex@Home Client has shut down" }
 
             try {
                 cache.close()
             } catch (e: IOException) {
                 LOGGER.error(e) { "Cache failed to close" }
             }
+
+            latch.countDown()
         }, 0, TimeUnit.SECONDS)
+
+        latch.await()
+        executor.shutdown()
+        LOGGER.info { "Mangadex@Home Client has shut down" }
     }
 
     /**