From 3a6ff8afca722493647ebcdce07a841c076cd2c9 Mon Sep 17 00:00:00 2001
From: Ethan Atkins <ethan.atkins@gmail.com>
Date: Tue, 30 Apr 2019 12:01:48 -0700
Subject: [PATCH] Use global classloader cache for scala instance

I noticed in a heap dump of sbt that there were many classloaders for
the scala instance. I then realized that we were making a new
classloader for the scala library on every test run. Even worse, the
ScalaInstanceLoader instance was never closed which lead to a metaspace
leak. I moved the scala instance classloader to the global classloader
cache. Not only will these be correctly cached, they will be closed if
evicted from the cache.
---
 .../main/scala/sbt/internal/ClassLoaders.scala | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/main/src/main/scala/sbt/internal/ClassLoaders.scala b/main/src/main/scala/sbt/internal/ClassLoaders.scala
index 6366343c8..ecd4fc50a 100644
--- a/main/src/main/scala/sbt/internal/ClassLoaders.scala
+++ b/main/src/main/scala/sbt/internal/ClassLoaders.scala
@@ -40,6 +40,7 @@ private[sbt] object ClassLoaders {
       rawRuntimeDependencies =
         dependencyJars(Runtime / dependencyClasspath).value.filterNot(exclude),
       allDependencies = dependencyJars(dependencyClasspath).value.filterNot(exclude),
+      globalCache = (Scope.GlobalScope / classLoaderCache).value,
       runtimeCache = (Runtime / classLoaderCache).value,
       testCache = (Test / classLoaderCache).value,
       resources = ClasspathUtilities.createClasspathResources(fullCP, si),
@@ -73,6 +74,7 @@ private[sbt] object ClassLoaders {
           )
           s.log.warn(s"$showJavaOptions will be ignored, $showFork is set to false")
         }
+        val globalCache = (Scope.GlobalScope / classLoaderCache).value
         val runtimeCache = (Runtime / classLoaderCache).value
         val testCache = (Test / classLoaderCache).value
         val exclude = dependencyJars(exportedProducts).value.toSet ++ instance.allJars
@@ -86,6 +88,7 @@ private[sbt] object ClassLoaders {
               fullCP = classpath,
               rawRuntimeDependencies = runtimeDeps,
               allDependencies = allDeps,
+              globalCache = globalCache,
               runtimeCache = runtimeCache,
               testCache = testCache,
               resources = ClasspathUtilities.createClasspathResources(classpath, instance),
@@ -114,6 +117,7 @@ private[sbt] object ClassLoaders {
       fullCP: Seq[File],
       rawRuntimeDependencies: Seq[File],
       allDependencies: Seq[File],
+      globalCache: ClassLoaderCache,
       runtimeCache: ClassLoaderCache,
       testCache: ClassLoaderCache,
       resources: Map[String, String],
@@ -143,7 +147,8 @@ private[sbt] object ClassLoaders {
         val allTestDependencies = if (layerTestDependencies) allDependenciesSet else Set.empty[File]
         val allRuntimeDependencies = (if (layerDependencies) rawRuntimeDependencies else Nil).toSet
 
-        val scalaInstanceLayer = new ScalaInstanceLoader(si)
+        val scalaInstanceLayer =
+          globalCache.get((si.allJars.toSeq, interfaceLoader, resources, tmp))
         // layer 2
         val runtimeDependencySet = allDependenciesSet intersect allRuntimeDependencies
         val runtimeDependencies = rawRuntimeDependencies.filter(runtimeDependencySet)
@@ -187,17 +192,6 @@ private[sbt] object ClassLoaders {
     if (snapshots.isEmpty) jarLoader else cache.get((snapshots, jarLoader, resources, tmp))
   }
 
-  private class ScalaInstanceLoader(val instance: ScalaInstance)
-      extends URLClassLoader(instance.allJars.map(_.toURI.toURL), interfaceLoader) {
-    override def equals(o: Any): Boolean = o match {
-      case that: ScalaInstanceLoader => this.instance.allJars.sameElements(that.instance.allJars)
-      case _                         => false
-    }
-    override def hashCode: Int = instance.hashCode
-    override lazy val toString: String =
-      s"ScalaInstanceLoader($interfaceLoader, jars = {${instance.allJars.mkString(", ")}})"
-  }
-
   // helper methods
   private def flatLoader(classpath: Seq[File], parent: ClassLoader): ClassLoader =
     new URLClassLoader(classpath.map(_.toURI.toURL).toArray, parent) {