add JavaModule#runBackground, to allow a task to kick off processes to run in the background that only die when the task is re-run

7 files changed, 150 insertions, 19 deletions

diff --git a/build.sc b/build.sc
index cc5115fa..f12c95ed 100755
--- a/build.sc
+++ b/build.sc
@@ -167,7 +167,16 @@ object scalalib extends MillModule {
       "-DMILL_SCALA_LIB=" + runClasspath().map(_.path).mkString(",")
     )
   }
-
+  object backgroundwrapper extends MillPublishModule{
+    def ivyDeps = Agg(
+      ivy"org.scala-sbt:test-interface:1.0"
+    )
+    def testArgs = T{
+      Seq(
+        "-DMILL_BACKGROUNDWRAPPER=" + runClasspath().map(_.path).mkString(",")
+      )
+    }
+  }
   object worker extends MillModule{
     def moduleDeps = Seq(main, scalalib)
 
@@ -190,7 +199,10 @@ object scalajslib extends MillModule {
       "MILL_SCALAJS_BRIDGE_0_6" -> jsbridges("0.6").compile().classes.path,
       "MILL_SCALAJS_BRIDGE_1_0" -> jsbridges("1.0").compile().classes.path
     )
-    Seq("-Djna.nosys=true") ++ scalalib.worker.testArgs() ++ (for((k, v) <- mapping.toSeq) yield s"-D$k=$v")
+    Seq("-Djna.nosys=true") ++
+    scalalib.worker.testArgs() ++
+    scalalib.backgroundwrapper.testArgs() ++
+    (for((k, v) <- mapping.toSeq) yield s"-D$k=$v")
   }
 
   object jsbridges extends Cross[JsBridgeModule]("0.6", "1.0")
@@ -232,7 +244,9 @@ object scalanativelib extends MillModule {
           .filter(_.toIO.exists)
           .mkString(",")
     )
-    scalalib.worker.testArgs() ++ (for((k, v) <- mapping.toSeq) yield s"-D$k=$v")
+    scalalib.worker.testArgs() ++
+    scalalib.backgroundwrapper.testArgs() ++
+    (for((k, v) <- mapping.toSeq) yield s"-D$k=$v")
   }
 
   object scalanativebridges extends Cross[ScalaNativeBridgeModule]("0.3")
@@ -276,6 +290,7 @@ object integration extends MillModule{
   def testArgs = T{
     scalajslib.testArgs() ++
     scalalib.worker.testArgs() ++
+    scalalib.backgroundwrapper.testArgs() ++
     scalanativelib.testArgs() ++
     Seq(
       "-DMILL_TESTNG=" + testng.runClasspath().map(_.path).mkString(","),
@@ -332,6 +347,7 @@ object dev extends MillModule{
       scalajslib.testArgs() ++
       scalalib.worker.testArgs() ++
       scalanativelib.testArgs() ++
+      scalalib.backgroundwrapper.testArgs() ++
       // Workaround for Zinc/JNA bug
       // https://github.com/sbt/sbt/blame/6718803ee6023ab041b045a6988fafcfae9d15b5/main/src/main/scala/sbt/Main.scala#L130
       Seq(
diff --git a/core/src/mill/define/Task.scala b/core/src/mill/define/Task.scala
index 63de11f6..d5f8680e 100644
--- a/core/src/mill/define/Task.scala
+++ b/core/src/mill/define/Task.scala
@@ -39,7 +39,6 @@ abstract class Task[+T] extends Task.Ops[T] with Applyable[Task, T]{
 
   def asTarget: Option[Target[T]] = None
   def asCommand: Option[Command[T]] = None
-  def asPersistent: Option[Persistent[T]] = None
   def asWorker: Option[Worker[T]] = None
   def self = this
 }
@@ -293,7 +292,6 @@ class Persistent[+T](t: Task[T],
   extends TargetImpl[T](t, ctx0, readWrite) {
 
   override def flushDest = false
-  override def asPersistent = Some(this)
 }
 class Input[T](t: Task[T],
                ctx0: mill.define.Ctx,
diff --git a/main/src/mill/modules/Jvm.scala b/main/src/mill/modules/Jvm.scala
index be683e4a..3a6dcb9f 100644
--- a/main/src/mill/modules/Jvm.scala
+++ b/main/src/mill/modules/Jvm.scala
@@ -26,20 +26,30 @@ object Jvm {
                             jvmArgs: Seq[String] = Seq.empty,
                             envArgs: Map[String, String] = Map.empty,
                             mainArgs: Seq[String] = Seq.empty,
-                            workingDir: Path = null): Unit = {
-    baseInteractiveSubprocess(
+                            workingDir: Path = null,
+                            background: Boolean = false): Unit = {
+    val args =
       Vector("java") ++
-        jvmArgs ++
-        Vector("-cp", classPath.mkString(File.pathSeparator), mainClass) ++
-        mainArgs,
-      envArgs,
-      workingDir
-    )
+      jvmArgs ++
+      Vector("-cp", classPath.mkString(File.pathSeparator), mainClass) ++
+      mainArgs
+
+    if (background) baseInteractiveSubprocess0(args, envArgs, workingDir)
+    else baseInteractiveSubprocess(args, envArgs, workingDir)
   }
 
   def baseInteractiveSubprocess(commandArgs: Seq[String],
                                 envArgs: Map[String, String],
                                 workingDir: Path) = {
+    val process = baseInteractiveSubprocess0(commandArgs, envArgs, workingDir)
+
+    val exitCode = process.waitFor()
+    if (exitCode == 0) ()
+    else throw InteractiveShelloutException()
+  }
+  def baseInteractiveSubprocess0(commandArgs: Seq[String],
+                                 envArgs: Map[String, String],
+                                 workingDir: Path) = {
     val builder = new java.lang.ProcessBuilder()
 
     for ((k, v) <- envArgs){
@@ -48,7 +58,7 @@ object Jvm {
     }
     builder.directory(workingDir.toIO)
 
-    val process = if (System.in.isInstanceOf[ByteArrayInputStream]){
+    if (System.in.isInstanceOf[ByteArrayInputStream]){
 
       val process = builder
         .command(commandArgs:_*)
@@ -71,11 +81,9 @@ object Jvm {
         .start()
     }
 
-    val exitCode = process.waitFor()
-    if (exitCode == 0) ()
-    else throw InteractiveShelloutException()
   }
 
+
   def runLocal(mainClass: String,
                classPath: Agg[Path],
                mainArgs: Seq[String] = Seq.empty)
diff --git a/main/src/mill/modules/Util.scala b/main/src/mill/modules/Util.scala
index da7407d0..2d71c13e 100644
--- a/main/src/mill/modules/Util.scala
+++ b/main/src/mill/modules/Util.scala
@@ -59,7 +59,8 @@ object Util {
   def millProjectModule(key: String,
                         artifact: String,
                         repositories: Seq[Repository],
-                        resolveFilter: Path => Boolean = _ => true) = {
+                        resolveFilter: Path => Boolean = _ => true,
+                        artifactSuffix: String = "_2.12") = {
     val localPath = sys.props(key)
     if (localPath != null) {
       mill.eval.Result.Success(
@@ -70,7 +71,7 @@ object Util {
         repositories,
         Seq(
           coursier.Dependency(
-            coursier.Module("com.lihaoyi", artifact + "_2.12"),
+            coursier.Module("com.lihaoyi", artifact + artifactSuffix),
             sys.props("MILL_VERSION")
           )
         ),
diff --git a/scalalib/backgroundwrapper/src/mill/scalalib/backgroundwrapper/BackgroundWrapper.java b/scalalib/backgroundwrapper/src/mill/scalalib/backgroundwrapper/BackgroundWrapper.java
new file mode 100644
index 00000000..64719b53
--- /dev/null
+++ b/scalalib/backgroundwrapper/src/mill/scalalib/backgroundwrapper/BackgroundWrapper.java
@@ -0,0 +1,40 @@
+package mill.scalalib.backgroundwrapper;
+
+public class BackgroundWrapper {
+    public static void main(String[] args) throws Exception{
+        String watched = args[0];
+        String tombstone = args[1];
+        String expected = args[2];
+        Thread watcher = new Thread(new Runnable() {
+            @Override
+            public void run() {
+                while (true) {
+                    try{
+                        Thread.sleep(10);
+                        String token = new String(
+                            java.nio.file.Files.readAllBytes(java.nio.file.Paths.get(watched))
+                        );
+                        if (!token.equals(expected)) {
+                            new java.io.File(tombstone).createNewFile();
+                            System.exit(0);
+                        }
+                    }catch(Exception e){
+                        try {
+                            new java.io.File(tombstone).createNewFile();
+                        }catch(Exception e2){}
+                        System.exit(0);
+                    }
+
+                }
+            }
+        });
+        watcher.setDaemon(true);
+        watcher.start();
+        String realMain = args[3];
+        String[] realArgs = new String[args.length - 4];
+        for(int i = 0; i < args.length-4; i++){
+            realArgs[i] = args[i+4];
+        }
+        Class.forName(realMain).getMethod("main", String[].class).invoke(null, (Object)realArgs);
+    }
+}
diff --git a/scalalib/src/mill/scalalib/JavaModule.scala b/scalalib/src/mill/scalalib/JavaModule.scala
index 3907b6a6..87dfb1b9 100644
--- a/scalalib/src/mill/scalalib/JavaModule.scala
+++ b/scalalib/src/mill/scalalib/JavaModule.scala
@@ -274,6 +274,67 @@ trait JavaModule extends mill.Module with TaskModule { outer =>
     }
   }
 
+  private[this] def backgroundSetup(dest: Path) = {
+    val token = java.util.UUID.randomUUID().toString
+    val procId = dest / ".mill-background-process-id"
+    val procTombstone = dest / ".mill-background-process-tombstone"
+    // The backgrounded subprocesses poll the procId file, and kill themselves
+    // when the procId file is deleted. This deletion happens immediately before
+    // the body of these commands run, but we cannot be sure the subprocess has
+    // had time to notice.
+    //
+    // To make sure we wait for the previous subprocess to
+    // die, we make the subprocess write a tombstone file out when it kills
+    // itself due to procId being deleted, and we wait a short time on task-start
+    // to see if such a tombstone appears. If a tombstone appears, we can be sure
+    // the subprocess has killed itself, and can continue. If a tombstone doesn't
+    // appear in a short amount of time, we assume the subprocess exited or was
+    // killed via some other means, and continue anyway.
+    val start = System.currentTimeMillis()
+    while({
+      if (exists(procTombstone)) {
+        Thread.sleep(10)
+        rm(procTombstone)
+        true
+      } else {
+        Thread.sleep(10)
+        System.currentTimeMillis() - start < 100
+      }
+    })()
+
+    write(procId, token)
+    write(procTombstone, token)
+    (procId, procTombstone, token)
+  }
+  def runBackground(args: String*) = T.command{
+    val (procId, procTombstone, token) = backgroundSetup(T.ctx().dest)
+    try Result.Success(Jvm.interactiveSubprocess(
+      "mill.scalalib.backgroundwrapper.BackgroundWrapper",
+      (runClasspath() ++ scalaWorker.backgroundWrapperClasspath()).map(_.path),
+      forkArgs(),
+      forkEnv(),
+      Seq(procId.toString, procTombstone.toString, token, finalMainClass()) ++ args,
+      workingDir = ammonite.ops.pwd,
+      background = true
+    )) catch { case e: InteractiveShelloutException =>
+       Result.Failure("subprocess failed")
+    }
+  }
+
+  def runMainBackground(mainClass: String, args: String*) = T.command{
+    val (procId, procTombstone, token) = backgroundSetup(T.ctx().dest)
+    try Result.Success(Jvm.interactiveSubprocess(
+      "mill.scalalib.backgroundwrapper.BackgroundWrapper",
+      (runClasspath() ++ scalaWorker.backgroundWrapperClasspath()).map(_.path),
+      forkArgs(),
+      forkEnv(),
+      Seq(procId.toString, procTombstone.toString, token, mainClass) ++ args,
+      workingDir = ammonite.ops.pwd,
+      background = true
+    )) catch { case e: InteractiveShelloutException =>
+      Result.Failure("subprocess failed")
+    }
+  }
 
   def runMainLocal(mainClass: String, args: String*) = T.command {
     Jvm.runLocal(
diff --git a/scalalib/src/mill/scalalib/ScalaWorkerApi.scala b/scalalib/src/mill/scalalib/ScalaWorkerApi.scala
index 6865c541..3d1a195a 100644
--- a/scalalib/src/mill/scalalib/ScalaWorkerApi.scala
+++ b/scalalib/src/mill/scalalib/ScalaWorkerApi.scala
@@ -29,6 +29,13 @@ trait ScalaWorkerModule extends mill.Module{
     mill.modules.Util.millProjectModule("MILL_SCALA_LIB", "mill-scalalib", repositories)
   }
 
+  def backgroundWrapperClasspath = T{
+    mill.modules.Util.millProjectModule(
+      "MILL_BACKGROUNDWRAPPER", "mill-scalalib-backgroundwrapper",
+      repositories, artifactSuffix = ""
+    )
+  }
+
   def worker: Worker[ScalaWorkerApi] = T.worker{
     val cl = mill.util.ClassLoader.create(
       classpath().map(_.path.toNIO.toUri.toURL).toVector,