dotty.tools.dotc.transform.LazyVals.scala Maven / Gradle / Ivy
package dotty.tools.dotc
package transform
import dotty.tools.dotc.core.Annotations.Annotation
import scala.collection.mutable
import core._
import Contexts._
import Symbols._
import Decorators._
import NameOps._
import NameKinds._
import StdNames.nme
import rewrite.Rewrites.patch
import util.Positions.Position
import dotty.tools.dotc.transform.MegaPhase._
import dotty.tools.dotc.ast.Trees._
import dotty.tools.dotc.ast.{untpd, tpd}
import dotty.tools.dotc.core.Constants.Constant
import dotty.tools.dotc.core.Types.{ExprType, NoType, MethodType}
import dotty.tools.dotc.core.Names.Name
import SymUtils._
import scala.collection.mutable.ListBuffer
import dotty.tools.dotc.core.Denotations.SingleDenotation
import dotty.tools.dotc.core.SymDenotations.SymDenotation
import dotty.tools.dotc.core.DenotTransformers.{SymTransformer, IdentityDenotTransformer, DenotTransformer}
import Erasure.Boxing.adaptToType
import java.util.IdentityHashMap
class LazyVals extends MiniPhase with IdentityDenotTransformer {
import LazyVals._
import tpd._
/** this map contains mutable state of transformation: OffsetDefs to be appended to companion object definitions,
* and number of bits currently used */
class OffsetInfo(var defs: List[Tree], var ord:Int)
val appendOffsetDefs = mutable.Map.empty[Symbol, OffsetInfo]
override def phaseName: String = "lazyVals"
/** List of names of phases that should have finished processing of tree
* before this phase starts processing same tree */
override def runsAfter = Set(Mixin.name, CollectNullableFields.name)
override def changesMembers = true // the phase adds lazy val accessors
def transformer = new LazyVals
val containerFlags = Flags.Synthetic | Flags.Mutable | Flags.Lazy
val initFlags = Flags.Synthetic | Flags.Method
val containerFlagsMask = Flags.Method | Flags.Lazy | Flags.Accessor | Flags.Module
/** A map of lazy values to the fields they should null after initialization. */
private[this] var lazyValNullables: IdentityHashMap[Symbol, mutable.ListBuffer[Symbol]] = _
private def nullableFor(sym: Symbol)(implicit ctx: Context) = {
// optimisation: value only used once, we can remove the value from the map
val nullables = lazyValNullables.remove(sym)
if (nullables == null) Nil
else nullables.toList
}
override def prepareForUnit(tree: Tree)(implicit ctx: Context) = {
if (lazyValNullables == null)
lazyValNullables = ctx.collectNullableFieldsPhase.asInstanceOf[CollectNullableFields].lazyValNullables
ctx
}
override def transformDefDef(tree: tpd.DefDef)(implicit ctx: Context): tpd.Tree =
transformLazyVal(tree)
override def transformValDef(tree: tpd.ValDef)(implicit ctx: Context): tpd.Tree = {
transformLazyVal(tree)
}
def transformLazyVal(tree: ValOrDefDef)(implicit ctx: Context): Tree = {
val sym = tree.symbol
if (!(sym is Flags.Lazy) ||
sym.owner.is(Flags.Trait) || // val is accessor, lazy field will be implemented in subclass
(sym.isStatic && sym.is(Flags.Module, butNot = Flags.Method))) // static module vals are implemented in the JVM by lazy loading
tree
else {
val isField = sym.owner.isClass
if (isField) {
if (sym.isVolatile ||
(sym.is(Flags.Module)/* || ctx.scala2Mode*/) &&
// TODO assume @volatile once LazyVals uses static helper constructs instead of
// ones in the companion object.
!sym.is(Flags.Synthetic))
// module class is user-defined.
// Should be threadsafe, to mimic safety guaranteed by global object
transformMemberDefVolatile(tree)
else if (sym.is(Flags.Module)) // synthetic module
transformSyntheticModule(tree)
else
transformMemberDefNonVolatile(tree)
}
else transformLocalDef(tree)
}
}
/** Append offset fields to companion objects
*/
override def transformTemplate(template: tpd.Template)(implicit ctx: Context): tpd.Tree = {
val cls = ctx.owner.asClass
appendOffsetDefs.get(cls) match {
case None => template
case Some(data) =>
data.defs.foreach(_.symbol.addAnnotation(Annotation(defn.ScalaStaticAnnot)))
cpy.Template(template)(body = addInFront(data.defs, template.body))
}
}
private def addInFront(prefix: List[Tree], stats: List[Tree]) = stats match {
case first :: rest if isSuperConstrCall(first) => first :: prefix ::: rest
case _ => prefix ::: stats
}
/** Make an eager val that would implement synthetic module.
* Eager val ensures thread safety and has less code generated.
*
*/
def transformSyntheticModule(tree: ValOrDefDef)(implicit ctx: Context) = {
val sym = tree.symbol
val holderSymbol = ctx.newSymbol(sym.owner, LazyLocalName.fresh(sym.asTerm.name),
Flags.Synthetic, sym.info.widen.resultType).enteredAfter(this)
val field = ValDef(holderSymbol, tree.rhs.changeOwnerAfter(sym, holderSymbol, this))
val getter = DefDef(sym.asTerm, ref(holderSymbol))
Thicket(field, getter)
}
/** Replace a local lazy val inside a method,
* with a LazyHolder from
* dotty.runtime(eg dotty.runtime.LazyInt)
*/
def transformLocalDef(x: ValOrDefDef)(implicit ctx: Context) = {
val valueInitter = x.rhs
val xname = x.name.asTermName
val holderName = LazyLocalName.fresh(xname)
val initName = LazyLocalInitName.fresh(xname)
val tpe = x.tpe.widen.resultType.widen
val holderType =
if (tpe isRef defn.IntClass) "LazyInt"
else if (tpe isRef defn.LongClass) "LazyLong"
else if (tpe isRef defn.BooleanClass) "LazyBoolean"
else if (tpe isRef defn.FloatClass) "LazyFloat"
else if (tpe isRef defn.DoubleClass) "LazyDouble"
else if (tpe isRef defn.ByteClass) "LazyByte"
else if (tpe isRef defn.CharClass) "LazyChar"
else if (tpe isRef defn.ShortClass) "LazyShort"
else "LazyRef"
val holderImpl = ctx.requiredClass("dotty.runtime." + holderType)
val holderSymbol = ctx.newSymbol(x.symbol.owner, holderName, containerFlags, holderImpl.typeRef, coord = x.pos)
val initSymbol = ctx.newSymbol(x.symbol.owner, initName, initFlags, MethodType(Nil, tpe), coord = x.pos)
val result = ref(holderSymbol).select(lazyNme.value).withPos(x.pos)
val flag = ref(holderSymbol).select(lazyNme.initialized)
val initer = valueInitter.changeOwnerAfter(x.symbol, initSymbol, this)
val initBody =
adaptToType(
ref(holderSymbol).select(defn.Object_synchronized).appliedTo(
adaptToType(mkNonThreadSafeDef(result, flag, initer, nullables = Nil), defn.ObjectType)),
tpe)
val initTree = DefDef(initSymbol, initBody)
val holderTree = ValDef(holderSymbol, New(holderImpl.typeRef, List()))
val methodBody = tpd.If(flag.ensureApplied,
result.ensureApplied,
ref(initSymbol).ensureApplied).ensureConforms(tpe)
val methodTree = DefDef(x.symbol.asTerm, methodBody)
ctx.debuglog(s"found a lazy val ${x.show},\nrewrote with ${holderTree.show}")
Thicket(holderTree, initTree, methodTree)
}
override def transformStats(trees: List[tpd.Tree])(implicit ctx: Context): List[tpd.Tree] = {
// backend requires field usage to be after field definition
// need to bring containers to start of method
val (holders, stats) =
trees.partition {
_.symbol.flags.&~(Flags.Touched) == containerFlags
// Filtering out Flags.Touched is not required currently, as there are no LazyTypes involved here
// but just to be more safe
}
holders:::stats
}
private def nullOut(nullables: List[Symbol])(implicit ctx: Context): List[Tree] = {
val nullConst = Literal(Constants.Constant(null))
nullables.map { field =>
assert(field.isField)
field.setFlag(Flags.Mutable)
ref(field).becomes(nullConst)
}
}
/** Create non-threadsafe lazy accessor equivalent to such code
* ```
* def methodSymbol() = {
* if (flag) target
* else {
* target = rhs
* flag = true
* nullable = null
* target
* }
* }
* }
* ```
*/
def mkNonThreadSafeDef(target: Tree, flag: Tree, rhs: Tree, nullables: List[Symbol])(implicit ctx: Context) = {
val setFlag = flag.becomes(Literal(Constants.Constant(true)))
val setNullables = nullOut(nullables)
val setTargetAndNullable = if (isWildcardArg(rhs)) setNullables else target.becomes(rhs) :: setNullables
val init = Block(setFlag :: setTargetAndNullable, target.ensureApplied)
If(flag.ensureApplied, target.ensureApplied, init)
}
/** Create non-threadsafe lazy accessor for not-nullable types equivalent to such code
* ```
* def methodSymbol() = {
* if (target eq null) {
* target = rhs
* nullable = null
* target
* } else target
* }
* ```
*/
def mkDefNonThreadSafeNonNullable(target: Symbol, rhs: Tree, nullables: List[Symbol])(implicit ctx: Context) = {
val cond = ref(target).select(nme.eq).appliedTo(Literal(Constant(null)))
val exp = ref(target)
val setTarget = exp.becomes(rhs)
val setNullables = nullOut(nullables)
val init = Block(setTarget :: setNullables, exp)
If(cond, init, exp)
}
def transformMemberDefNonVolatile(x: ValOrDefDef)(implicit ctx: Context) = {
val claz = x.symbol.owner.asClass
val tpe = x.tpe.widen.resultType.widen
assert(!(x.symbol is Flags.Mutable))
val containerName = LazyLocalName.fresh(x.name.asTermName)
val containerSymbol = ctx.newSymbol(claz, containerName,
x.symbol.flags &~ containerFlagsMask | containerFlags | Flags.Private,
tpe, coord = x.symbol.coord
).enteredAfter(this)
val containerTree = ValDef(containerSymbol, defaultValue(tpe))
if (x.tpe.isNotNull && tpe <:< defn.ObjectType) { // can use 'null' value instead of flag
val slowPath = DefDef(x.symbol.asTerm, mkDefNonThreadSafeNonNullable(containerSymbol, x.rhs, nullableFor(x.symbol)))
Thicket(containerTree, slowPath)
}
else {
val flagName = LazyBitMapName.fresh(x.name.asTermName)
val flagSymbol = ctx.newSymbol(x.symbol.owner, flagName, containerFlags | Flags.Private, defn.BooleanType).enteredAfter(this)
val flag = ValDef(flagSymbol, Literal(Constants.Constant(false)))
val slowPath = DefDef(x.symbol.asTerm, mkNonThreadSafeDef(ref(containerSymbol), ref(flagSymbol), x.rhs, nullableFor(x.symbol)))
Thicket(containerTree, flag, slowPath)
}
}
/** Create a threadsafe lazy accessor equivalent to such code
* ```
* def methodSymbol(): Int = {
* val result: Int = 0
* val retry: Boolean = true
* var flag: Long = 0L
* while retry do {
* flag = dotty.runtime.LazyVals.get(this, $claz.$OFFSET)
* dotty.runtime.LazyVals.STATE(flag, 0) match {
* case 0 =>
* if dotty.runtime.LazyVals.CAS(this, $claz.$OFFSET, flag, 1, $ord) {
* try {result = rhs} catch {
* case x: Throwable =>
* dotty.runtime.LazyVals.setFlag(this, $claz.$OFFSET, 0, $ord)
* throw x
* }
* $target = result
* dotty.runtime.LazyVals.setFlag(this, $claz.$OFFSET, 3, $ord)
* retry = false
* }
* case 1 =>
* dotty.runtime.LazyVals.wait4Notification(this, $claz.$OFFSET, flag, $ord)
* case 2 =>
* dotty.runtime.LazyVals.wait4Notification(this, $claz.$OFFSET, flag, $ord)
* case 3 =>
* retry = false
* result = $target
* }
* }
* nullable = null
* result
* }
* ```
*/
def mkThreadSafeDef(methodSymbol: TermSymbol,
claz: ClassSymbol,
ord: Int,
target: Symbol,
rhs: Tree,
tp: Types.Type,
offset: Tree,
getFlag: Tree,
stateMask: Tree,
casFlag: Tree,
setFlagState: Tree,
waitOnLock: Tree,
nullables: List[Symbol])(implicit ctx: Context) = {
val initState = Literal(Constants.Constant(0))
val computeState = Literal(Constants.Constant(1))
val notifyState = Literal(Constants.Constant(2))
val computedState = Literal(Constants.Constant(3))
val flagSymbol = ctx.newSymbol(methodSymbol, lazyNme.flag, containerFlags, defn.LongType)
val flagDef = ValDef(flagSymbol, Literal(Constant(0L)))
val thiz = This(claz)(ctx.fresh.setOwner(claz))
val resultSymbol = ctx.newSymbol(methodSymbol, lazyNme.result, containerFlags, tp)
val resultDef = ValDef(resultSymbol, defaultValue(tp))
val retrySymbol = ctx.newSymbol(methodSymbol, lazyNme.retry, containerFlags, defn.BooleanType)
val retryDef = ValDef(retrySymbol, Literal(Constants.Constant(true)))
val whileCond = ref(retrySymbol)
val compute = {
val handlerSymbol = ctx.newSymbol(methodSymbol, nme.ANON_FUN, Flags.Synthetic,
MethodType(List(nme.x_1), List(defn.ThrowableType), defn.IntType))
val caseSymbol = ctx.newSymbol(methodSymbol, nme.DEFAULT_EXCEPTION_NAME, Flags.Synthetic, defn.ThrowableType)
val triggerRetry = setFlagState.appliedTo(thiz, offset, initState, Literal(Constant(ord)))
val complete = setFlagState.appliedTo(thiz, offset, computedState, Literal(Constant(ord)))
val handler = CaseDef(Bind(caseSymbol, ref(caseSymbol)), EmptyTree,
Block(List(triggerRetry), Throw(ref(caseSymbol))
))
val compute = ref(resultSymbol).becomes(rhs)
val tr = Try(compute, List(handler), EmptyTree)
val assign = ref(target).becomes(ref(resultSymbol))
val noRetry = ref(retrySymbol).becomes(Literal(Constants.Constant(false)))
val body = If(casFlag.appliedTo(thiz, offset, ref(flagSymbol), computeState, Literal(Constant(ord))),
Block(tr :: assign :: complete :: noRetry :: Nil, Literal(Constant(()))),
Literal(Constant(())))
CaseDef(initState, EmptyTree, body)
}
val waitFirst = {
val wait = waitOnLock.appliedTo(thiz, offset, ref(flagSymbol), Literal(Constant(ord)))
CaseDef(computeState, EmptyTree, wait)
}
val waitSecond = {
val wait = waitOnLock.appliedTo(thiz, offset, ref(flagSymbol), Literal(Constant(ord)))
CaseDef(notifyState, EmptyTree, wait)
}
val computed = {
val noRetry = ref(retrySymbol).becomes(Literal(Constants.Constant(false)))
val result = ref(resultSymbol).becomes(ref(target))
val body = Block(noRetry :: result :: Nil, Literal(Constant(())))
CaseDef(computedState, EmptyTree, body)
}
val default = CaseDef(Underscore(defn.LongType), EmptyTree, Literal(Constant(())))
val cases = Match(stateMask.appliedTo(ref(flagSymbol), Literal(Constant(ord))),
List(compute, waitFirst, waitSecond, computed, default)) //todo: annotate with @switch
val whileBody = List(ref(flagSymbol).becomes(getFlag.appliedTo(thiz, offset)), cases)
val cycle = WhileDo(methodSymbol, whileCond, whileBody)
val setNullables = nullOut(nullables)
DefDef(methodSymbol, Block(resultDef :: retryDef :: flagDef :: cycle :: setNullables, ref(resultSymbol)))
}
def transformMemberDefVolatile(x: ValOrDefDef)(implicit ctx: Context) = {
assert(!(x.symbol is Flags.Mutable))
val tpe = x.tpe.widen.resultType.widen
val claz = x.symbol.owner.asClass
val thizClass = Literal(Constant(claz.info))
val helperModule = ctx.requiredModule("dotty.runtime.LazyVals")
val getOffset = Select(ref(helperModule), lazyNme.RLazyVals.getOffset)
var offsetSymbol: TermSymbol = null
var flag: Tree = EmptyTree
var ord = 0
def offsetName(id: Int) = (StdNames.nme.LAZY_FIELD_OFFSET + (if(x.symbol.owner.is(Flags.Module)) "_m_" else "") + id.toString).toTermName
// compute or create appropriate offsetSymol, bitmap and bits used by current ValDef
appendOffsetDefs.get(claz) match {
case Some(info) =>
val flagsPerLong = (64 / dotty.runtime.LazyVals.BITS_PER_LAZY_VAL).toInt
info.ord += 1
ord = info.ord % flagsPerLong
val id = info.ord / flagsPerLong
val offsetById = offsetName(id)
if (ord != 0) { // there are unused bits in already existing flag
offsetSymbol = claz.info.decl(offsetById)
.suchThat(sym => (sym is Flags.Synthetic) && sym.isTerm)
.symbol.asTerm
} else { // need to create a new flag
offsetSymbol = ctx.newSymbol(claz, offsetById, Flags.Synthetic, defn.LongType).enteredAfter(this)
offsetSymbol.addAnnotation(Annotation(defn.ScalaStaticAnnot))
val flagName = (StdNames.nme.BITMAP_PREFIX + id.toString).toTermName
val flagSymbol = ctx.newSymbol(claz, flagName, containerFlags, defn.LongType).enteredAfter(this)
flag = ValDef(flagSymbol, Literal(Constants.Constant(0L)))
val offsetTree = ValDef(offsetSymbol, getOffset.appliedTo(thizClass, Literal(Constant(flagName.toString))))
info.defs = offsetTree :: info.defs
}
case None =>
offsetSymbol = ctx.newSymbol(claz, offsetName(0), Flags.Synthetic, defn.LongType).enteredAfter(this)
offsetSymbol.addAnnotation(Annotation(defn.ScalaStaticAnnot))
val flagName = (StdNames.nme.BITMAP_PREFIX + "0").toTermName
val flagSymbol = ctx.newSymbol(claz, flagName, containerFlags, defn.LongType).enteredAfter(this)
flag = ValDef(flagSymbol, Literal(Constants.Constant(0L)))
val offsetTree = ValDef(offsetSymbol, getOffset.appliedTo(thizClass, Literal(Constant(flagName.toString))))
appendOffsetDefs += (claz -> new OffsetInfo(List(offsetTree), ord))
}
val containerName = LazyLocalName.fresh(x.name.asTermName)
val containerSymbol = ctx.newSymbol(claz, containerName, x.symbol.flags &~ containerFlagsMask | containerFlags, tpe, coord = x.symbol.coord).enteredAfter(this)
val containerTree = ValDef(containerSymbol, defaultValue(tpe))
val offset = ref(offsetSymbol)
val getFlag = Select(ref(helperModule), lazyNme.RLazyVals.get)
val setFlag = Select(ref(helperModule), lazyNme.RLazyVals.setFlag)
val wait = Select(ref(helperModule), lazyNme.RLazyVals.wait4Notification)
val state = Select(ref(helperModule), lazyNme.RLazyVals.state)
val cas = Select(ref(helperModule), lazyNme.RLazyVals.cas)
val nullables = nullableFor(x.symbol)
val accessor = mkThreadSafeDef(x.symbol.asTerm, claz, ord, containerSymbol, x.rhs, tpe, offset, getFlag, state, cas, setFlag, wait, nullables)
if (flag eq EmptyTree)
Thicket(containerTree, accessor)
else Thicket(containerTree, flag, accessor)
}
}
object LazyVals {
object lazyNme {
object RLazyVals {
import dotty.runtime.LazyVals._
val get = Names.get.toTermName
val setFlag = Names.setFlag.toTermName
val wait4Notification = Names.wait4Notification.toTermName
val state = Names.state.toTermName
val cas = Names.cas.toTermName
val getOffset = Names.getOffset.toTermName
}
val flag = "flag".toTermName
val result = "result".toTermName
val value = "value".toTermName
val initialized = "initialized".toTermName
val retry = "retry".toTermName
}
}
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