SI-8131 fixes residual race condition in runtime reflection

Apparently some completers can call setInfo while they’re not yet done,
which resets the LOCKED flag, and makes anything that uses LOCKED to
track completion unreliable. Unfortunately, that’s exactly the mechanism
that was used by runtime reflection to elide locking for symbols that are
known to be initialized.

This commit fixes the problematic lock elision strategy by introducing
an explicit communication channel between SynchronizedSymbol’s and their
completers. Now instead of trying hard to infer whether it’s already
initialized or not, every symbol gets a volatile field that can be queried
to provide necessary information.

1 files changed, 9 insertions, 3 deletions

diff --git a/src/reflect/scala/reflect/internal/pickling/UnPickler.scala b/src/reflect/scala/reflect/internal/pickling/UnPickler.scala
index 3d222fce10..2f3e726787 100644
--- a/src/reflect/scala/reflect/internal/pickling/UnPickler.scala
+++ b/src/reflect/scala/reflect/internal/pickling/UnPickler.scala
@@ -275,6 +275,7 @@ abstract class UnPickler {
       def pflags       = flags & PickledFlags
 
       def finishSym(sym: Symbol): Symbol = {
+        markFlagsCompleted(sym)(mask = AllFlags)
         sym.privateWithin = privateWithin
         sym.info = (
           if (atEnd) {
@@ -663,7 +664,7 @@ abstract class UnPickler {
     private class LazyTypeRef(i: Int) extends LazyType with FlagAgnosticCompleter {
       private val definedAtRunId = currentRunId
       private val p = phase
-      override def complete(sym: Symbol) : Unit = try {
+      protected def completeInternal(sym: Symbol) : Unit = try {
         val tp = at(i, () => readType(sym.isTerm)) // after NMT_TRANSITION, revert `() => readType(sym.isTerm)` to `readType`
         if (p ne null)
           slowButSafeEnteringPhase(p) (sym setInfo tp)
@@ -673,6 +674,10 @@ abstract class UnPickler {
       catch {
         case e: MissingRequirementError => throw toTypeError(e)
       }
+      override def complete(sym: Symbol) : Unit = {
+        completeInternal(sym)
+        if (!isCompilerUniverse) markAllCompleted(sym)
+      }
       override def load(sym: Symbol) { complete(sym) }
     }
 
@@ -680,8 +685,9 @@ abstract class UnPickler {
      *  of completed symbol to symbol at index `j`.
      */
     private class LazyTypeRefAndAlias(i: Int, j: Int) extends LazyTypeRef(i) {
-      override def complete(sym: Symbol) = try {
-        super.complete(sym)
+      override def completeInternal(sym: Symbol) = try {
+        super.completeInternal(sym)
+
         var alias = at(j, readSymbol)
         if (alias.isOverloaded)
           alias = slowButSafeEnteringPhase(picklerPhase)((alias suchThat (alt => sym.tpe =:= sym.owner.thisType.memberType(alt))))