Make sure background jobs are shut down

main/src/main/scala/sbt/BackgroundJobService.scala

@@ -13,7 +13,8 @@ abstract class BackgroundJobService extends Closeable {
    *  then you could process.destroy() for example.
    */
   def runInBackground(spawningTask: ScopedKey[_], state: State)(start: (Logger) => Unit): JobHandle
-  def close: Unit = ()
+  def close(): Unit
+  def shutdown(): Unit
   def jobs: Vector[JobHandle]
   def stop(job: JobHandle): Unit
   def waitFor(job: JobHandle): Unit

main/src/main/scala/sbt/Defaults.scala

@@ -134,12 +134,10 @@ object Defaults extends BuildCommon {
       includeFilter in unmanagedJars :== "*.jar" | "*.so" | "*.dll" | "*.jnilib" | "*.zip",
       includeFilter in unmanagedResources :== AllPassFilter,
       fileToStore :== DefaultFileToStore,
-      bgJobService := { new DefaultBackgroundJobService() },
       bgList := { bgJobService.value.jobs },
       ps := psTask.value,
       bgStop := bgStopTask.evaluated,
-      bgWaitFor := bgWaitForTask.evaluated,
-      onUnload := { s => try onUnload.value(s) finally bgJobService.value.close() }
+      bgWaitFor := bgWaitForTask.evaluated
     )
 
   private[sbt] lazy val globalIvyCore: Seq[Setting[_]] =

main/src/main/scala/sbt/Main.scala

@@ -20,7 +20,8 @@ import sbt.internal.{
   Script,
   SessionSettings,
   SettingCompletions,
-  LogManager
+  LogManager,
+  DefaultBackgroundJobService
 }
 import sbt.internal.util.{ AttributeKey, AttributeMap, complete, ConsoleOut, GlobalLogging, LineRange, MainAppender, SimpleReader, Types }
 import sbt.util.{ Level, Logger }
@@ -81,8 +82,11 @@ object StandardMain {
   def runManaged(s: State): xsbti.MainResult =
     {
       val previous = TrapExit.installManager()
-      try MainLoop.runLogged(s)
-      finally TrapExit.uninstallManager(previous)
+      try {
+        try {
+          MainLoop.runLogged(s)
+        } finally DefaultBackgroundJobService.backgroundJobService.shutdown()
+      } finally TrapExit.uninstallManager(previous)
     }
 
   /** The common interface to standard output, used for all built-in ConsoleLoggers. */

main/src/main/scala/sbt/internal/DefaultBackgroundJobService.scala

@@ -1,12 +1,12 @@
 package sbt
 package internal
 
-import java.util.concurrent.atomic.{ AtomicLong, AtomicInteger }
+import java.util.concurrent.atomic.AtomicLong
 import java.io.Closeable
-import sbt.util.{ Logger, LogExchange, Level }
-import sbt.internal.util.MainAppender
-import Def.ScopedKey
+import sbt.util.Logger
+import Def.{ ScopedKey, Setting }
 import scala.concurrent.ExecutionContext
+import Scope.GlobalScope
 
 /**
  * Interface between sbt and a thing running in the background.
@@ -99,7 +99,8 @@ private[sbt] abstract class AbstractBackgroundJobService extends BackgroundJobSe
     pool.run(this, spawningTask, state)(start)
   }
 
-  override def close(): Unit = {
+  override final def close(): Unit = shutdown()
+  override def shutdown(): Unit = {
     while (jobSet.nonEmpty) {
       jobSet.headOption.foreach {
         case handle: ThreadJobHandle @unchecked =>
@@ -259,10 +260,13 @@ private[sbt] class BackgroundThreadPool extends java.io.Closeable {
 }
 
 private[sbt] class DefaultBackgroundJobService extends AbstractBackgroundJobService {
-  private val generateId: AtomicInteger = new AtomicInteger
-
   override def makeContext(id: Long, spawningTask: ScopedKey[_], state: State): Logger = {
     val extracted = Project.extract(state)
     LogManager.constructBackgroundLog(extracted.structure.data, state)(spawningTask)
   }
 }
+private[sbt] object DefaultBackgroundJobService {
+  lazy val backgroundJobService: DefaultBackgroundJobService = new DefaultBackgroundJobService
+  lazy val backgroundJobServiceSetting: Setting[_] =
+    ((Keys.bgJobService in GlobalScope) :== backgroundJobService)
+}

main/src/main/scala/sbt/internal/Load.scala

@@ -89,6 +89,7 @@ private[sbt] object Load {
   def injectGlobal(state: State): Seq[Setting[_]] =
     (appConfiguration in GlobalScope :== state.configuration) +:
       LogManager.settingsLogger(state) +:
+      DefaultBackgroundJobService.backgroundJobServiceSetting +:
       EvaluateTask.injectSettings
   def defaultWithGlobal(state: State, base: File, rawConfig: LoadBuildConfiguration, globalBase: File, log: Logger): LoadBuildConfiguration =
     {