Fix for #2365.

a soft reference around cached classes so they do not interfere with
garbage collection. There is a test case, but it is in pending because I
spent longer trying to get it to fail under partest than I did writing
the actual patch. If you would like to see the behavior which was
corrected, go to

  test/pending/run/bug2365

and run that script with scalac built before and after this commit.
Review by dubochet.

4 files changed, 28 insertions, 32 deletions

diff --git a/src/compiler/scala/tools/nsc/ast/TreeDSL.scala b/src/compiler/scala/tools/nsc/ast/TreeDSL.scala
index fb65f82740..a788015262 100644
--- a/src/compiler/scala/tools/nsc/ast/TreeDSL.scala
+++ b/src/compiler/scala/tools/nsc/ast/TreeDSL.scala
@@ -175,7 +175,10 @@ trait TreeDSL {
         if (target.tpe.typeSymbol == SomeClass) TRUE   // is Some[_]
         else NOT(ID(target) DOT nme.isEmpty)           // is Option[_]
 
-      def GET() = fn(ID(target), nme.get)
+      def IS_NULL() = REF(target) ANY_EQ NULL
+      def NOT_NULL() = REF(target) ANY_NE NULL
+
+      def GET() = fn(REF(target), nme.get)
 
       // name of nth indexed argument to a method (first parameter list), defaults to 1st
       def ARG(idx: Int = 0) = Ident(target.paramss.head(idx))
diff --git a/src/compiler/scala/tools/nsc/ast/TreeGen.scala b/src/compiler/scala/tools/nsc/ast/TreeGen.scala
index c5a8b93c88..7f2bcf99c5 100644
--- a/src/compiler/scala/tools/nsc/ast/TreeGen.scala
+++ b/src/compiler/scala/tools/nsc/ast/TreeGen.scala
@@ -228,6 +228,9 @@ abstract class TreeGen
   def mkOr(tree1: Tree, tree2: Tree): Tree =
     Apply(Select(tree1, Boolean_or), List(tree2))
 
+  // wrap the given expression in a SoftReference so it can be gc-ed
+  def mkSoftRef(expr: Tree): Tree = New(TypeTree(SoftReferenceClass.tpe), List(List(expr)))
+
   def mkCached(cvar: Symbol, expr: Tree): Tree = {
     val cvarRef = if (cvar.owner.isClass) Select(This(cvar.owner), cvar) else Ident(cvar)
     Block(
diff --git a/src/compiler/scala/tools/nsc/symtab/Definitions.scala b/src/compiler/scala/tools/nsc/symtab/Definitions.scala
index e1cf7a5a7e..e14a7d796c 100644
--- a/src/compiler/scala/tools/nsc/symtab/Definitions.scala
+++ b/src/compiler/scala/tools/nsc/symtab/Definitions.scala
@@ -219,6 +219,8 @@ trait Definitions {
       def ArrayModule_apply = getMember(ArrayModule, nme.apply)
 
     // reflection / structural types
+    lazy val SoftReferenceClass     = getClass("java.lang.ref.SoftReference")
+    lazy val WeakReferenceClass     = getClass("java.lang.ref.WeakReference")
     lazy val MethodClass            = getClass(sn.MethodAsObject)
     lazy val EmptyMethodCacheClass  = getClass("scala.runtime.EmptyMethodCache")
     lazy val MethodCacheClass       = getClass("scala.runtime.MethodCache")
diff --git a/src/compiler/scala/tools/nsc/transform/CleanUp.scala b/src/compiler/scala/tools/nsc/transform/CleanUp.scala
index cf217dcd23..c508400711 100644
--- a/src/compiler/scala/tools/nsc/transform/CleanUp.scala
+++ b/src/compiler/scala/tools/nsc/transform/CleanUp.scala
@@ -52,27 +52,6 @@ abstract class CleanUp extends Transform with ast.TreeDSL {
     private def typedWithPos(pos: Position)(tree: Tree) =
       localTyper typed { atPos(pos)(tree) }
 
-    private def classConstantMethod(pos: Position, sig: String): Symbol =
-      classConstantMeth.getOrElseUpdate(sig, {
-        val forName = getMember(ClassClass.linkedModuleOfClass, nme.forName)
-        val owner = currentOwner.enclClass
-
-        val cvar = owner.newVariable(pos, unit.fresh.newName(pos, "class$Cache"))
-          .setFlag(PRIVATE | STATIC | MUTABLE | SYNTHETIC).setInfo(ClassClass.tpe)
-        owner.info.decls enter cvar
-        val cdef = typedWithPos(pos) { VAL(cvar) === NULL }
-
-        val meth = owner.newMethod(pos, unit.fresh.newName(pos, "class$Method"))
-          .setFlag(PRIVATE | STATIC | SYNTHETIC).setInfo(MethodType(List(), ClassClass.tpe))
-        owner.info.decls enter meth
-        val mdef = typedWithPos(pos)(DEF(meth) ===
-          gen.mkCached(cvar, Apply(REF(forName), List(Literal(sig))))
-        )
-
-        newDefs.append(cdef, mdef)
-        meth
-      })
-
     override def transformUnit(unit: CompilationUnit) =
       unit.body = transform(unit.body)
 
@@ -185,7 +164,8 @@ abstract class CleanUp extends Transform with ast.TreeDSL {
 
             case MONO_CACHE =>
 
-              /* Implementation of the cache is as follows for method "def xyz(a: A, b: B)":
+              /* Implementation of the cache is as follows for method "def xyz(a: A, b: B)"
+                 (but with a SoftReference wrapping reflClass$Cache, similarly in the poly Cache) :
 
                 var reflParams$Cache: Array[Class[_]] = Array[JClass](classOf[A], classOf[B])
 
@@ -210,16 +190,19 @@ abstract class CleanUp extends Transform with ast.TreeDSL {
                 addStaticVariableToClass("reflMethod$Cache", MethodClass.tpe, NULL, false)
 
               val reflClassCacheSym: Symbol =
-                addStaticVariableToClass("reflClass$Cache", ClassClass.tpe, NULL, false)
+                addStaticVariableToClass("reflClass$Cache", SoftReferenceClass.tpe, NULL, false)
 
               def getMethodSym = ClassClass.tpe member nme.getMethod_
 
+              def isCacheEmpty(receiver: Symbol): Tree =
+                reflClassCacheSym.IS_NULL() OR (reflClassCacheSym.GET() ANY_NE REF(receiver))
+
               addStaticMethodToClass("reflMethod$Method", List(ClassClass.tpe), MethodClass.tpe) {
                 case Pair(reflMethodSym, List(forReceiverSym)) =>
                   BLOCK(
-                    IF (REF(reflClassCacheSym) ANY_NE REF(forReceiverSym)) THEN BLOCK(
+                    IF (isCacheEmpty(forReceiverSym)) THEN BLOCK(
                       REF(reflMethodCacheSym) === ((REF(forReceiverSym) DOT getMethodSym)(LIT(method), REF(reflParamsCacheSym))) ,
-                      REF(reflClassCacheSym) === REF(forReceiverSym),
+                      REF(reflClassCacheSym) === gen.mkSoftRef(REF(forReceiverSym)),
                       UNIT
                     ) ENDIF,
                     REF(reflMethodCacheSym)
@@ -228,7 +211,10 @@ abstract class CleanUp extends Transform with ast.TreeDSL {
 
             case POLY_CACHE =>
 
-              /* Implementation of the cache is as follows for method "def xyz(a: A, b: B)":
+              /* Implementation of the cache is as follows for method "def xyz(a: A, b: B)"
+                 (but with the addition of a SoftReference wrapped around the MethodCache holder
+                 so that it does not interfere with classloader garbage collection, see ticket
+                 #2365 for details):
 
                 var reflParams$Cache: Array[Class[_]] = Array[JClass](classOf[A], classOf[B])
 
@@ -250,23 +236,25 @@ abstract class CleanUp extends Transform with ast.TreeDSL {
               val reflParamsCacheSym: Symbol =
                 addStaticVariableToClass("reflParams$Cache", theTypeClassArray, fromTypesToClassArrayLiteral(paramTypes), true)
 
-              val reflPolyCacheSym: Symbol =
-                addStaticVariableToClass("reflPoly$Cache", MethodCacheClass.tpe, NEW(TypeTree(EmptyMethodCacheClass.tpe)), false)
+              def mkNewPolyCache = gen.mkSoftRef(NEW(TypeTree(EmptyMethodCacheClass.tpe)))
+              val reflPolyCacheSym: Symbol = addStaticVariableToClass("reflPoly$Cache", SoftReferenceClass.tpe, mkNewPolyCache, false)
+              def getPolyCache = fn(REF(reflPolyCacheSym), nme.get) AS_ATTR MethodCacheClass.tpe
 
               addStaticMethodToClass("reflMethod$Method", List(ClassClass.tpe), MethodClass.tpe)
                 { case Pair(reflMethodSym, List(forReceiverSym)) =>
                   val methodSym = reflMethodSym.newVariable(ad.pos, mkTerm("method")) setInfo MethodClass.tpe
 
                   BLOCK(
-                    VAL(methodSym) === ((REF(reflPolyCacheSym) DOT methodCache_find)(REF(forReceiverSym))) ,
+                    IF (getPolyCache ANY_EQ NULL) THEN (REF(reflPolyCacheSym) === mkNewPolyCache) ENDIF,
+                    VAL(methodSym) === ((getPolyCache DOT methodCache_find)(REF(forReceiverSym))) ,
                     IF (REF(methodSym) OBJ_!= NULL) .
                       THEN (Return(REF(methodSym)))
                     ELSE {
                       def methodSymRHS  = ((REF(forReceiverSym) DOT Class_getMethod)(LIT(method), REF(reflParamsCacheSym)))
-                      def cacheRHS      = ((REF(reflPolyCacheSym) DOT methodCache_add)(REF(forReceiverSym), REF(methodSym)))
+                      def cacheRHS      = ((getPolyCache DOT methodCache_add)(REF(forReceiverSym), REF(methodSym)))
                       BLOCK(
                         REF(methodSym)        === methodSymRHS,
-                        REF(reflPolyCacheSym) === cacheRHS,
+                        REF(reflPolyCacheSym) === gen.mkSoftRef(cacheRHS),
                         Return(REF(methodSym))
                       )
                     }