optimizes Scala reflection GIL

First of all, GIL should only apply to runtime reflection, because noone
is going to run toolboxes in multiple threads: a) that's impossible, b/c
the compiler isn't thread safe, b) ToolBox api prevents that.

Secondly, the only things in symbols which require synchronization are:
1) info/validTo (completers aren't thread-safe),
2) rawInfo and its dependencies (it shares a mutable field with info)
3) non-trivial caches like in typeAsMemberOfLock

If you think about it, other things like sourceModule or associatedFile
don't need synchronization, because they are either set up when a symbol
is created or cloned or when it's completed. The former is obviously safe,
while the latter is safe as well, because before acquiring init-dependent
state of symbols, the compiler calls `initialize`, which is synchronized.

We can say that symbols can be in four possible states: 1) being created,
2) created, but not yet initialized, 3) initializing, 4) initialized.
Of those only #3 is dangerous and needs protection, which is what this
commit does.

1 files changed, 10 insertions, 3 deletions

diff --git a/src/reflect/scala/reflect/internal/Symbols.scala b/src/reflect/scala/reflect/internal/Symbols.scala
index a7abe08c2e..a54a17901a 100644
--- a/src/reflect/scala/reflect/internal/Symbols.scala
+++ b/src/reflect/scala/reflect/internal/Symbols.scala
@@ -951,6 +951,13 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
     final def isInitialized: Boolean =
       validTo != NoPeriod
 
+    /** Some completers call sym.setInfo when still in-flight and then proceed with initialization (e.g. see LazyPackageType)
+     *  setInfo sets _validTo to current period, which means that after a call to setInfo isInitialized will start returning true.
+     *  Unfortunately, this doesn't mean that info becomes ready to be used, because subsequent initialization might change the info.
+     *  Therefore we need this method to distinguish between initialized and really initialized symbol states.
+     */
+    final def isFullyInitialized: Boolean = _validTo != NoPeriod && (flags & LOCKED) == 0
+
     /** Can this symbol be loaded by a reflective mirror?
      *
      *  Scalac relies on `ScalaSignature' annotation to retain symbols across compilation runs.
@@ -3129,8 +3136,8 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
     override def thisType: Type = {
       val period = thisTypePeriod
       if (period != currentPeriod) {
-        thisTypePeriod = currentPeriod
         if (!isValid(period)) thisTypeCache = ThisType(this)
+        thisTypePeriod = currentPeriod
       }
       thisTypeCache
     }
@@ -3218,9 +3225,9 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
     override def typeOfThis = {
       val period = typeOfThisPeriod
       if (period != currentPeriod) {
-        typeOfThisPeriod = currentPeriod
         if (!isValid(period))
           typeOfThisCache = singleType(owner.thisType, sourceModule)
+        typeOfThisPeriod = currentPeriod
       }
       typeOfThisCache
     }
@@ -3231,9 +3238,9 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
         // Skip a package object class, because the members are also in
         // the package and we wish to avoid spurious ambiguities as in pos/t3999.
         if (!isPackageObjectClass) {
+          implicitMembersCacheValue = tp.implicitMembers
           implicitMembersCacheKey1 = tp
           implicitMembersCacheKey2 = tp.decls.elems
-          implicitMembersCacheValue = tp.implicitMembers
         }
       }
       implicitMembersCacheValue