Fix thread safety problem in runtime reflection

src/compiler/scala/tools/nsc/symtab/SymbolLoaders.scala

@@ -312,7 +312,7 @@ abstract class SymbolLoaders {
       }
     }
   }
-  private val classFileDataReader: ReusableInstance[ReusableDataReader] = ReusableInstance[ReusableDataReader](new ReusableDataReader())
+  private lazy val classFileDataReader: ReusableInstance[ReusableDataReader] = ReusableInstance[ReusableDataReader](new ReusableDataReader(), enabled = isCompilerUniverse)
   class ClassfileLoader(val classfile: AbstractFile, clazz: ClassSymbol, module: ModuleSymbol) extends SymbolLoader with FlagAssigningCompleter {
     private object classfileParser extends {
       val symbolTable: SymbolLoaders.this.symbolTable.type = SymbolLoaders.this.symbolTable

src/compiler/scala/tools/nsc/typechecker/Contexts.scala

@@ -1355,7 +1355,7 @@ trait Contexts { self: Analyzer =>
    *  the search continuing as long as no qualifying name is found.
    */
   // OPT: moved this into a (cached) object to avoid costly and non-eliminated {Object,Int}Ref allocations
-  private[Contexts] final val symbolLookupCache = ReusableInstance[SymbolLookup](new SymbolLookup)
+  private[Contexts] final val symbolLookupCache = ReusableInstance[SymbolLookup](new SymbolLookup, enabled = isCompilerUniverse)
   private[Contexts] final class SymbolLookup {
     private[this] var lookupError: NameLookup  = _ // set to non-null if a definite error is encountered
     private[this] var inaccessible: NameLookup = _ // records inaccessible symbol for error reporting in case none is found

src/compiler/scala/tools/nsc/typechecker/Implicits.scala

@@ -1919,7 +1919,7 @@ trait Implicits {
     def isShadowed(name: Name): Boolean
   }
   object Shadower {
-    private[this] val localShadowerCache = ReusableInstance[LocalShadower](new LocalShadower)
+    private[this] val localShadowerCache = ReusableInstance[LocalShadower](new LocalShadower, enabled = isCompilerUniverse)
 
     def using[T](local: Boolean)(f: Shadower => T): T =
       if (local) localShadowerCache.using { shadower =>

src/reflect/scala/reflect/internal/Positions.scala

@@ -298,7 +298,7 @@ trait Positions extends api.Positions { self: SymbolTable =>
       inform("error while set children pos "+pos+" of "+parent.children)
       throw ex
   }
-  private val setChildrenPosAccumulator = ReusableInstance[SetChildrenPosAccumulator](new SetChildrenPosAccumulator)
+  private val setChildrenPosAccumulator = ReusableInstance[SetChildrenPosAccumulator](new SetChildrenPosAccumulator, enabled = isCompilerUniverse)
   private final class SetChildrenPosAccumulator extends (Tree => Boolean) {
     private[this] val wrappingPosAccumulator = new WrappingPosAccumulator
     private[this] var pos: Position = _

src/reflect/scala/reflect/internal/Trees.scala

@@ -2050,7 +2050,7 @@ trait Trees extends api.Trees {
       }
     }
   }
-  private val onlyChildAccumulator = ReusableInstance[OnlyChildAccumulator](new OnlyChildAccumulator)
+  private val onlyChildAccumulator = ReusableInstance[OnlyChildAccumulator](new OnlyChildAccumulator, enabled = isCompilerUniverse)
 
 // -------------- Classtags --------------------------------------------------------
 

src/reflect/scala/reflect/internal/Variances.scala

@@ -269,7 +269,7 @@ trait Variances {
   final def varianceInType(tp: Type, considerUnchecked: Boolean = false)(tparam: Symbol): Variance =
     varianceInTypeCache.using(_.apply(tp, tparam, considerUnchecked))
 
-  private[this] val varianceInTypeCache = ReusableInstance[varianceInType](new varianceInType)
+  private[this] val varianceInTypeCache = ReusableInstance[varianceInType](new varianceInType, enabled = isCompilerUniverse)
 
   private final class varianceInType {
     private[this] var tp: Type = _

src/reflect/scala/reflect/internal/tpe/TypeConstraints.scala

@@ -199,7 +199,7 @@ private[internal] trait TypeConstraints {
     }
   }
 
-  private[this] val containsCollectorInstances: ReusableInstance[ContainsCollector] = ReusableInstance(new ContainsCollector(null))
+  private[this] val containsCollectorInstances: ReusableInstance[ContainsCollector] = ReusableInstance(new ContainsCollector(null), enabled = isCompilerUniverse)
 
   private[this] def containsSymbol(tp: Type, sym: Symbol): Boolean =
     containsCollectorInstances.using { cc =>