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.

4 files changed, 41 insertions, 65 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
diff --git a/src/reflect/scala/reflect/runtime/Gil.scala b/src/reflect/scala/reflect/runtime/Gil.scala
index 8a8bfebf8c..cf6f1431d7 100644
--- a/src/reflect/scala/reflect/runtime/Gil.scala
+++ b/src/reflect/scala/reflect/runtime/Gil.scala
@@ -12,11 +12,14 @@ private[reflect] trait Gil {
   lazy val gil = new java.util.concurrent.locks.ReentrantLock
 
   @inline final def gilSynchronized[T](body: => T): T = {
-    try {
-      gil.lock()
-      body
-    } finally {
-      gil.unlock()
+    if (isCompilerUniverse) body
+    else {
+      try {
+        gil.lock()
+        body
+      } finally {
+        gil.unlock()
+      }
     }
   }
 }
diff --git a/src/reflect/scala/reflect/runtime/SynchronizedOps.scala b/src/reflect/scala/reflect/runtime/SynchronizedOps.scala
index 21df973297..c90901410a 100644
--- a/src/reflect/scala/reflect/runtime/SynchronizedOps.scala
+++ b/src/reflect/scala/reflect/runtime/SynchronizedOps.scala
@@ -44,7 +44,7 @@ private[reflect] trait SynchronizedOps extends internal.SymbolTable
     // we can keep this lock fine-grained, because methods of Scope don't do anything extraordinary, which makes deadlocks impossible
     // fancy subclasses of internal.Scopes#Scope should do synchronization themselves (e.g. see PackageScope for an example)
     private lazy val syncLock = new Object
-    def syncLockSynchronized[T](body: => T): T = syncLock.synchronized { body }
+    def syncLockSynchronized[T](body: => T): T = if (isCompilerUniverse) body else syncLock.synchronized { body }
     override def isEmpty: Boolean = syncLockSynchronized { super.isEmpty }
     override def size: Int = syncLockSynchronized { super.size }
     override def enter[T <: Symbol](sym: T): T = syncLockSynchronized { super.enter(sym) }
diff --git a/src/reflect/scala/reflect/runtime/SynchronizedSymbols.scala b/src/reflect/scala/reflect/runtime/SynchronizedSymbols.scala
index a52921c5c6..7f08e8fbe2 100644
--- a/src/reflect/scala/reflect/runtime/SynchronizedSymbols.scala
+++ b/src/reflect/scala/reflect/runtime/SynchronizedSymbols.scala
@@ -29,27 +29,16 @@ private[reflect] trait SynchronizedSymbols extends internal.Symbols { self: Symb
 
   trait SynchronizedSymbol extends Symbol {
 
-    override def rawflags = gilSynchronized { super.rawflags }
-    override def rawflags_=(x: Long) = gilSynchronized { super.rawflags_=(x) }
-
-    override def rawowner = gilSynchronized { super.rawowner }
-    override def owner_=(owner: Symbol) = gilSynchronized { super.owner_=(owner) }
-
-    override def validTo = gilSynchronized { super.validTo }
-    override def validTo_=(x: Period) = gilSynchronized { super.validTo_=(x) }
-
-    override def pos = gilSynchronized { super.pos }
-    override def setPos(pos: Position): this.type = { gilSynchronized { super.setPos(pos) }; this }
-
-    override def privateWithin = gilSynchronized { super.privateWithin }
-    override def privateWithin_=(sym: Symbol) = gilSynchronized { super.privateWithin_=(sym) }
+    def gilSynchronizedIfNotInited[T](body: => T): T = {
+      if (isFullyInitialized) body
+      else gilSynchronized { body }
+    }
 
-    override def info = gilSynchronized { super.info }
-    override def info_=(info: Type) = gilSynchronized { super.info_=(info) }
-    override def updateInfo(info: Type): Symbol = gilSynchronized { super.updateInfo(info) }
-    override def rawInfo: Type = gilSynchronized { super.rawInfo }
+    override def validTo = gilSynchronizedIfNotInited { super.validTo }
+    override def info = gilSynchronizedIfNotInited { super.info }
+    override def rawInfo: Type = gilSynchronizedIfNotInited { super.rawInfo }
 
-    override def typeParams: List[Symbol] = gilSynchronized {
+    override def typeParams: List[Symbol] = gilSynchronizedIfNotInited {
       if (isCompilerUniverse) super.typeParams
       else {
         if (isMonomorphicType) Nil
@@ -65,7 +54,7 @@ private[reflect] trait SynchronizedSymbols extends internal.Symbols { self: Symb
         }
       }
     }
-    override def unsafeTypeParams: List[Symbol] = gilSynchronized {
+    override def unsafeTypeParams: List[Symbol] = gilSynchronizedIfNotInited {
       if (isCompilerUniverse) super.unsafeTypeParams
       else {
         if (isMonomorphicType) Nil
@@ -73,14 +62,6 @@ private[reflect] trait SynchronizedSymbols extends internal.Symbols { self: Symb
       }
     }
 
-    override def reset(completer: Type): this.type = gilSynchronized { super.reset(completer) }
-
-    override def infosString: String = gilSynchronized { super.infosString }
-
-    override def annotations: List[AnnotationInfo] = gilSynchronized { super.annotations }
-    override def setAnnotations(annots: List[AnnotationInfo]): this.type = { gilSynchronized { super.setAnnotations(annots) }; this }
-
-
 // ------ creators -------------------------------------------------------------------
 
     override protected def createAbstractTypeSymbol(name: TypeName, pos: Position, newFlags: Long): AbstractTypeSymbol =
@@ -128,41 +109,26 @@ private[reflect] trait SynchronizedSymbols extends internal.Symbols { self: Symb
 
 // ------- subclasses ---------------------------------------------------------------------
 
-  trait SynchronizedTermSymbol extends TermSymbol with SynchronizedSymbol {
-    override def name_=(x: Name) = gilSynchronized { super.name_=(x) }
-    override def rawname = gilSynchronized { super.rawname }
-    override def referenced: Symbol = gilSynchronized { super.referenced }
-    override def referenced_=(x: Symbol) = gilSynchronized { super.referenced_=(x) }
-  }
+  trait SynchronizedTermSymbol extends SynchronizedSymbol
 
   trait SynchronizedMethodSymbol extends MethodSymbol with SynchronizedTermSymbol {
-    override def typeAsMemberOf(pre: Type): Type = gilSynchronized { super.typeAsMemberOf(pre) }
-    override def paramss: List[List[Symbol]] = gilSynchronized { super.paramss }
-    override def returnType: Type = gilSynchronized { super.returnType }
+    // we can keep this lock fine-grained, because it's just a cache over asSeenFrom, which makes deadlocks impossible
+    // unfortunately we cannot elide this lock, because the cache depends on `pre`
+    private lazy val typeAsMemberOfLock = new Object
+    override def typeAsMemberOf(pre: Type): Type = gilSynchronizedIfNotInited { typeAsMemberOfLock.synchronized { super.typeAsMemberOf(pre) } }
   }
 
+  trait SynchronizedModuleSymbol extends ModuleSymbol with SynchronizedTermSymbol
+
   trait SynchronizedTypeSymbol extends TypeSymbol with SynchronizedSymbol {
-    override def name_=(x: Name) = gilSynchronized { super.name_=(x) }
-    override def rawname = gilSynchronized { super.rawname }
-    override def typeConstructor: Type = gilSynchronized { super.typeConstructor }
-    override def tpe_* : Type = gilSynchronized { super.tpe_* }
-    override def tpeHK : Type = gilSynchronized { super.tpeHK }
+    // unlike with typeConstructor, a lock is necessary here, because tpe calculation relies on
+    // temporarily assigning NoType to tpeCache to detect cyclic reference errors
+    private lazy val tpeLock = new Object
+    override def tpe_* : Type = gilSynchronizedIfNotInited { tpeLock.synchronized { super.tpe_* } }
   }
 
-  trait SynchronizedClassSymbol extends ClassSymbol with SynchronizedTypeSymbol {
-    override def associatedFile = gilSynchronized { super.associatedFile }
-    override def associatedFile_=(f: AbstractFile) = gilSynchronized { super.associatedFile_=(f) }
-    override def thisSym: Symbol = gilSynchronized { super.thisSym }
-    override def thisType: Type = gilSynchronized { super.thisType }
-    override def typeOfThis: Type = gilSynchronized { super.typeOfThis }
-    override def typeOfThis_=(tp: Type) = gilSynchronized { super.typeOfThis_=(tp) }
-    override def children = gilSynchronized { super.children }
-    override def addChild(sym: Symbol) = gilSynchronized { super.addChild(sym) }
-  }
+  trait SynchronizedClassSymbol extends ClassSymbol with SynchronizedTypeSymbol
 
-  trait SynchronizedModuleClassSymbol extends ModuleClassSymbol with SynchronizedClassSymbol {
-    override def sourceModule = gilSynchronized { super.sourceModule }
-    override def implicitMembers: Scope = gilSynchronized { super.implicitMembers }
-  }
+  trait SynchronizedModuleClassSymbol extends ModuleClassSymbol with SynchronizedClassSymbol
 }