Use lock file to control access to boot directory during update

launch/Launch.scala

@@ -72,10 +72,12 @@ final class RunConfiguration(val scalaVersion: String, val app: xsbti.Applicatio
 import BootConfiguration.{appDirectoryName, baseDirectoryName, ScalaDirectoryName, TestLoadScalaClasses}
 class Launch(val bootDirectory: File, repositories: List[Repository]) extends xsbti.Launcher
 {
+	bootDirectory.mkdirs
 	private val scalaProviders = new Cache[String, ScalaProvider](new ScalaProvider(_))
 	def getScala(version: String): xsbti.ScalaProvider = scalaProviders(version)
 
 	lazy val topLoader = new BootFilteredLoader(getClass.getClassLoader)
+	val updateLockFile = new File(bootDirectory, "sbt.boot.lock")
 
 	def globalLock: xsbti.GlobalLock = Locks
 
@@ -93,6 +95,7 @@ class Launch(val bootDirectory: File, repositories: List[Repository]) extends xs
 		def testLoadClasses = TestLoadScalaClasses
 		def target = UpdateScala
 		def failLabel = "Scala " + version
+		def lockFile = updateLockFile
 
 		def app(id: xsbti.ApplicationID): xsbti.AppProvider = new AppProvider(id)
 
@@ -106,6 +109,7 @@ class Launch(val bootDirectory: File, repositories: List[Repository]) extends xs
 			def testLoadClasses = List(id.mainClass)
 			def target = new UpdateApp(Application(id))
 			def failLabel = id.name + " " + id.version
+			def lockFile = updateLockFile
 
 			lazy val mainClass: Class[T] forSome { type T <: xsbti.AppMain } =
 			{
@@ -121,7 +125,7 @@ class Launch(val bootDirectory: File, repositories: List[Repository]) extends xs
 class ComponentProvider(baseDirectory: File) extends xsbti.ComponentProvider
 {
 	def componentLocation(id: String): File = new File(baseDirectory, id)
-	def component(id: String) = GetJars.wrapNull(componentLocation(id).listFiles).filter(_.isFile)
+	def component(id: String) = Provider.wrapNull(componentLocation(id).listFiles).filter(_.isFile)
 	def defineComponent(id: String, files: Array[File]) =
 	{
 		val location = componentLocation(id)

launch/Locks.scala

@@ -8,7 +8,7 @@ import java.util.concurrent.Callable
 object Locks extends xsbti.GlobalLock
 {
 	private[this] val locks = new Cache[File, GlobalLock](new GlobalLock(_))
-	def apply[T](file: File, action: Callable[T]) =
+	def apply[T](file: File, action: Callable[T]): T =
 		synchronized { locks(file.getCanonicalFile).withLock(action) }
 
 	private[this] class GlobalLock(file: File)

launch/Provider.scala

@@ -3,6 +3,7 @@ package xsbt.boot
 import Pre._
 import java.io.{File, FileFilter}
 import java.net.{URL, URLClassLoader}
+import java.util.concurrent.Callable
 
 trait Provider extends NotNull
 {
@@ -12,39 +13,41 @@ trait Provider extends NotNull
 	def target: UpdateTarget
 	def failLabel: String
 	def parentLoader: ClassLoader
+	def lockFile: File
 
-	val (jars, loader) =
+	val (jars, loader) = Locks(lockFile, new initialize)
+	private final class initialize extends Callable[(Array[File], ClassLoader)]
 	{
-		val (existingJars, existingLoader) = createLoader
-		if(Check.needsUpdate(existingLoader, testLoadClasses))
+		def call =
 		{
-			( new Update(configuration) )(target)
-			val (newJars, newLoader) = createLoader
-			Check.failIfMissing(newLoader, testLoadClasses, failLabel)
-			(newJars, newLoader)
+			val (existingJars, existingLoader) = createLoader
+			if(Provider.needsUpdate(existingLoader, testLoadClasses))
+			{
+				( new Update(configuration) )(target)
+				val (newJars, newLoader) = createLoader
+				Provider.failIfMissing(newLoader, testLoadClasses, failLabel)
+				(newJars, newLoader)
+			}
+			else
+				(existingJars, existingLoader)
+		}
+		def createLoader =
+		{
+			val jars = Provider.getJars(baseDirectories)
+			(jars, new URLClassLoader(jars.map(_.toURI.toURL), parentLoader) )
 		}
-		else
-			(existingJars, existingLoader)
-	}
-	def createLoader =
-	{
-		 val jars = GetJars(baseDirectories)
-		(jars, new URLClassLoader(jars.map(_.toURI.toURL), parentLoader) )
 	}
 }
 
-object GetJars
+object Provider
 {
-	def apply(directories: List[File]): Array[File] = toArray(directories.flatMap(directory => wrapNull(directory.listFiles(JarFilter))))
+	def getJars(directories: List[File]): Array[File] = toArray(directories.flatMap(directory => wrapNull(directory.listFiles(JarFilter))))
 	def wrapNull(a: Array[File]): Array[File] = if(a == null) Array() else a
 
 	object JarFilter extends FileFilter
 	{
 		def accept(file: File) = !file.isDirectory && file.getName.endsWith(".jar")
 	}
-}
-object Check
-{
 	def failIfMissing(loader: ClassLoader, classes: Iterable[String], label: String) =
 		checkTarget(loader, classes, (), missing => error("Could not retrieve " + label + ": missing " + missing.mkString(", ")))
 	def needsUpdate(loader: ClassLoader, classes: Iterable[String]) = checkTarget(loader, classes, false, x => true)