Use java to implement XMain classloaders

These classloaders which are created if sbt is launched with a legacy
launcher (or one that doesn't follow the current classloading hierarchy
convention), were implemented in scala, but that meant that they were
not parallel capable. I fix that by moving the implementations to java.
I also move the static method that creates a MetaBuildLoader into the
java class.

main/src/main/java/sbt/internal/FullScalaLoader.java

@@ -0,0 +1,36 @@
+/*
+ * sbt
+ * Copyright 2011 - 2018, Lightbend, Inc.
+ * Copyright 2008 - 2010, Mark Harrah
+ * Licensed under Apache License 2.0 (see LICENSE)
+ */
+
+package sbt.internal;
+
+import java.net.URL;
+import java.net.URLClassLoader;
+
+final class FullScalaLoader extends URLClassLoader {
+  private final String jarString;
+
+  FullScalaLoader(final URL[] scalaRest, final URLClassLoader parent) {
+    super(scalaRest, parent);
+    final StringBuilder res = new StringBuilder();
+    int i = 0;
+    while (i < scalaRest.length) {
+      res.append(scalaRest[i].getPath());
+      res.append(", ");
+      i += 1;
+    }
+    jarString = res.toString();
+  }
+
+  @Override
+  public String toString() {
+    return "ScalaClassLoader(jars = " + jarString + ")";
+  }
+
+  static {
+    registerAsParallelCapable();
+  }
+}

main/src/main/java/sbt/internal/MetaBuildLoader.java

@@ -0,0 +1,104 @@
+/*
+ * sbt
+ * Copyright 2011 - 2018, Lightbend, Inc.
+ * Copyright 2008 - 2010, Mark Harrah
+ * Licensed under Apache License 2.0 (see LICENSE)
+ */
+
+package sbt.internal;
+
+import java.io.File;
+import java.io.IOException;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.util.regex.Pattern;
+import xsbti.AppProvider;
+import xsbti.ScalaProvider;
+
+@SuppressWarnings("unused")
+public final class MetaBuildLoader extends URLClassLoader {
+  private final URLClassLoader fullScalaLoader;
+  private final URLClassLoader libraryLoader;
+  private final URLClassLoader interfaceLoader;
+  MetaBuildLoader(
+      final URL[] urls,
+      final URLClassLoader fullScalaLoader,
+      final URLClassLoader libraryLoader,
+      final URLClassLoader interfaceLoader) {
+    super(urls, fullScalaLoader);
+    this.fullScalaLoader = fullScalaLoader;
+    this.libraryLoader = libraryLoader;
+    this.interfaceLoader = interfaceLoader;
+  }
+
+  @Override
+  public String toString() {
+    return "SbtMetaBuildClassLoader";
+  }
+
+  @Override
+  public void close() throws IOException {
+    super.close();
+    fullScalaLoader.close();
+    libraryLoader.close();
+    interfaceLoader.close();
+  }
+
+  static {
+    ClassLoader.registerAsParallelCapable();
+  }
+
+  /**
+   *  Rearrange the classloaders so that test-interface is above the scala library. Implemented
+   *  without using the scala standard library to minimize classloading.
+   *
+   * @param appProvider the appProvider that needs to be modified
+   * @return a ClassLoader with a URLClassLoader for the test-interface-1.0.jar above the
+   *         scala library.
+   */
+  public static MetaBuildLoader makeLoader(final AppProvider appProvider) throws IOException {
+    final Pattern pattern = Pattern.compile("test-interface-[0-9.]+\\.jar");
+    final File[] cp = appProvider.mainClasspath();
+    final URL[] interfaceURL = new URL[1];
+    final URL[] rest = new URL[cp.length - 1];
+
+    {
+      int i = 0;
+      int j = 0; // index into rest
+      while (i < cp.length) {
+        final File file = cp[i];
+        if (pattern.matcher(file.getName()).find()) {
+          interfaceURL[0] = file.toURI().toURL();
+        } else {
+          rest[j] = file.toURI().toURL();
+          j += 1;
+        }
+        i += 1;
+      }
+    }
+    final ScalaProvider scalaProvider = appProvider.scalaProvider();
+    final ClassLoader topLoader = scalaProvider.launcher().topLoader();
+    final TestInterfaceLoader interfaceLoader = new TestInterfaceLoader(interfaceURL, topLoader);
+    final File[] siJars = scalaProvider.jars();
+    final URL[] lib = new URL[1];
+    final URL[] scalaRest = new URL[siJars.length - 1];
+
+    {
+      int i = 0;
+      int j = 0; // index into scalaRest
+      while (i < siJars.length) {
+        final File file = siJars[i];
+        if (file.getName().equals("scala-library.jar")) {
+          lib[0] = file.toURI().toURL();
+        } else {
+          scalaRest[j] = file.toURI().toURL();
+          j += 1;
+        }
+        i += 1;
+      }
+    }
+    final ScalaLibraryClassLoader libraryLoader = new ScalaLibraryClassLoader(lib, interfaceLoader);
+    final FullScalaLoader fullScalaLoader = new FullScalaLoader(scalaRest, libraryLoader);
+    return new MetaBuildLoader(rest, fullScalaLoader, libraryLoader, interfaceLoader);
+  }
+}

main/src/main/java/sbt/internal/TestInterfaceLoader.java

@@ -0,0 +1,26 @@
+/*
+ * sbt
+ * Copyright 2011 - 2018, Lightbend, Inc.
+ * Copyright 2008 - 2010, Mark Harrah
+ * Licensed under Apache License 2.0 (see LICENSE)
+ */
+
+package sbt.internal;
+
+import java.net.URL;
+import java.net.URLClassLoader;
+
+class TestInterfaceLoader extends URLClassLoader {
+  TestInterfaceLoader(final URL[] urls, final ClassLoader parent) {
+    super(urls, parent);
+  }
+
+  @Override
+  public String toString() {
+    return "SbtTestInterfaceClassLoader(" + getURLs()[0] + ")";
+  }
+
+  static {
+    registerAsParallelCapable();
+  }
+}

main/src/main/java/sbt/internal/XMainClassLoader.java

@@ -0,0 +1,34 @@
+/*
+ * sbt
+ * Copyright 2011 - 2018, Lightbend, Inc.
+ * Copyright 2008 - 2010, Mark Harrah
+ * Licensed under Apache License 2.0 (see LICENSE)
+ */
+
+package sbt.internal;
+
+import java.net.URL;
+import java.net.URLClassLoader;
+
+class XMainClassLoader extends URLClassLoader {
+  XMainClassLoader(final URL[] urls, final ClassLoader parent) {
+    super(urls, parent);
+  }
+
+  @Override
+  protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
+    if (name.startsWith("sbt.internal.XMainConfiguration")) {
+      synchronized (getClassLoadingLock(name)) {
+        Class<?> result = findLoadedClass(name);
+        if (result == null) result = findClass(name);
+        if (resolve) resolveClass(result);
+        return result;
+      }
+    }
+    return super.loadClass(name, resolve);
+  }
+
+  static {
+    registerAsParallelCapable();
+  }
+}

main/src/main/scala/sbt/internal/XMainConfiguration.scala

@@ -9,9 +9,8 @@ package sbt.internal
 
 import java.io.File
 import java.lang.reflect.InvocationTargetException
-import java.net.{ URL, URLClassLoader }
+import java.net.URL
 import java.util.concurrent.{ ExecutorService, Executors }
-import java.util.regex.Pattern
 
 import sbt.plugins.{ CorePlugin, IvyPlugin, JvmPlugin }
 import sbt.util.LogExchange
@@ -93,28 +92,19 @@ private[sbt] class XMainConfiguration {
     val topLoader = configuration.provider.scalaProvider.launcher.topLoader
     // This loader doesn't have the scala library in it so it's critical that none of the code
     // in this file use the scala library.
-    val modifiedLoader = new URLClassLoader(urlArray, topLoader) {
-      override def loadClass(name: String, resolve: Boolean): Class[_] = {
-        if (name.startsWith("sbt.internal.XMainConfiguration")) {
-          val clazz = findClass(name)
-          if (resolve) resolveClass(clazz)
-          clazz
-        } else {
-          super.loadClass(name, resolve)
-        }
-      }
-    }
+    val modifiedLoader = new XMainClassLoader(urlArray, topLoader)
     val xMainConfigurationClass = modifiedLoader.loadClass("sbt.internal.XMainConfiguration")
     val instance: AnyRef =
       xMainConfigurationClass.getConstructor().newInstance().asInstanceOf[AnyRef]
 
-    val method = xMainConfigurationClass.getMethod("makeLoader", classOf[AppProvider])
-    val modifiedConfigurationClass =
-      modifiedLoader.loadClass("sbt.internal.XMainConfiguration$ModifiedConfiguration")
+    val metaBuildLoaderClass = modifiedLoader.loadClass("sbt.internal.MetaBuildLoader")
+    val method = metaBuildLoaderClass.getMethod("makeLoader", classOf[AppProvider])
 
-    val loader = method.invoke(instance, configuration.provider).asInstanceOf[ClassLoader]
+    val loader = method.invoke(null, configuration.provider).asInstanceOf[ClassLoader]
 
     Thread.currentThread.setContextClassLoader(loader)
+    val modifiedConfigurationClass =
+      modifiedLoader.loadClass("sbt.internal.XMainConfiguration$ModifiedConfiguration")
     val cons = modifiedConfigurationClass.getConstructors()(0)
     close(configuration.provider.loader)
     val scalaProvider = configuration.provider.scalaProvider
@@ -187,84 +177,4 @@ private[sbt] class XMainConfiguration {
     override def provider(): AppProvider = new ModifiedAppProvider(configuration.provider)
   }
 
-  /**
-   *  Rearrange the classloaders so that test-interface is above the scala library. Implemented
-   *  without using the scala standard library to minimize classloading.
-   * @param appProvider the appProvider that needs to be modified
-   * @return a ClassLoader with a URLClassLoader for the test-interface-1.0.jar above the
-   *         scala library.
-   */
-  private[sbt] def makeLoader(appProvider: AppProvider): ClassLoader = {
-    val pattern = Pattern.compile("test-interface-[0-9.]+\\.jar")
-    val cp = appProvider.mainClasspath
-    val interfaceURL = new Array[URL](1)
-    val rest = new Array[URL](cp.length - 1)
-
-    {
-      var i = 0
-      var j = 0 // index into rest
-      while (i < cp.length) {
-        val file = cp(i)
-        if (pattern.matcher(file.getName).find()) {
-          interfaceURL(0) = file.toURI.toURL
-        } else {
-          rest(j) = file.toURI.toURL
-          j += 1
-        }
-        i += 1
-      }
-    }
-    val scalaProvider = appProvider.scalaProvider
-    val topLoader = scalaProvider.launcher.topLoader
-    class InterfaceLoader extends URLClassLoader(interfaceURL, topLoader) {
-      override def toString: String = "SbtTestInterfaceClassLoader(" + interfaceURL(0) + ")"
-    }
-    val interfaceLoader = new InterfaceLoader
-    val siJars = scalaProvider.jars
-    val lib = new Array[URL](1)
-    val scalaRest = new Array[URL](siJars.length - 1)
-
-    {
-      var i = 0
-      var j = 0 // index into scalaRest
-      while (i < siJars.length) {
-        val file = siJars(i)
-        if (file.getName.equals("scala-library.jar")) {
-          lib(0) = file.toURI.toURL
-        } else {
-          scalaRest(j) = file.toURI.toURL
-          j += 1
-        }
-        i += 1
-      }
-    }
-    class LibraryLoader extends URLClassLoader(lib, interfaceLoader) {
-      override def toString: String = "ScalaLibraryLoader( " + lib(0) + ")"
-    }
-    val libraryLoader = new LibraryLoader
-    class FullLoader extends URLClassLoader(scalaRest, libraryLoader) {
-      private val jarString: String = {
-        val res = new java.lang.StringBuilder
-        var i = 0
-        while (i < scalaRest.length) {
-          res.append(scalaRest(i).getPath)
-          res.append(", ")
-          i += 1
-        }
-        res.toString
-      }
-      override def toString: String = "ScalaClassLoader(jars = " + jarString + ")"
-    }
-    val fullLoader = new FullLoader
-    class MetaBuildLoader extends URLClassLoader(rest, fullLoader) {
-      override def toString: String = "SbtMetaBuildClassLoader"
-      override def close(): Unit = {
-        super.close()
-        libraryLoader.close()
-        fullLoader.close()
-        interfaceLoader.close()
-      }
-    }
-    new MetaBuildLoader
-  }
 }