New version of Lazy Vals implementation

Author: szymon-rd

bench-run/src/main/scala/dotty/tools/benchmarks/lazyvals/ContendedInitialization.scala

@@ -0,0 +1,49 @@
+package dotty.tools.benchmarks.lazyvals
+
+import org.openjdk.jmh.annotations._
+import LazyVals.LazyHolder
+import org.openjdk.jmh.infra.Blackhole
+import java.util.concurrent.TimeUnit
+import java.util.concurrent.{Executors, ExecutorService}
+
+@BenchmarkMode(Array(Mode.AverageTime))
+@Fork(2)
+@Threads(1)
+@Warmup(iterations = 5)
+@Measurement(iterations = 5)
+@OutputTimeUnit(TimeUnit.MILLISECONDS)
+@State(Scope.Benchmark)
+class ContendedInitialization {
+
+  @Param(Array("2000000", "5000000"))
+  var size: Int = _
+
+  @Param(Array("2", "4", "8"))
+  var nThreads: Int = _
+
+  var executor: ExecutorService = _
+
+  @Setup
+  def prepare: Unit = {
+    executor = Executors.newFixedThreadPool(nThreads)
+  }
+
+  @TearDown
+  def cleanup: Unit = {
+    executor.shutdown()
+    executor = null
+  }
+
+  @Benchmark
+  def measureContended(bh: Blackhole): Unit = {
+    val array = Array.fill(size)(new LazyHolder)
+    val task: Runnable = () =>
+    for (elem <- array) bh.consume(elem.value)
+
+    val futures =
+    for (_ <- 0 until nThreads) yield
+      executor.submit(task)
+
+    futures.foreach(_.get())
+  }
+}

bench-run/src/main/scala/dotty/tools/benchmarks/lazyvals/InitializedAccess.scala

@@ -0,0 +1,29 @@
+package dotty.tools.benchmarks.lazyvals
+
+import org.openjdk.jmh.annotations._
+import LazyVals.LazyHolder
+import org.openjdk.jmh.infra.Blackhole
+import java.util.concurrent.TimeUnit
+
+@BenchmarkMode(Array(Mode.AverageTime))
+@Fork(2)
+@Threads(1)
+@Warmup(iterations = 5)
+@Measurement(iterations = 5)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@State(Scope.Benchmark)
+class InitializedAccess {
+
+    var holder: LazyHolder = _
+
+    @Setup
+    def prepare: Unit = {
+      holder = new LazyHolder
+      holder.value
+    }
+
+    @Benchmark
+    def measureInitialized(bh: Blackhole) = {
+        bh.consume(holder.value)
+    }
+}

bench-run/src/main/scala/dotty/tools/benchmarks/lazyvals/LazyVals.scala

@@ -0,0 +1,7 @@
+package dotty.tools.benchmarks.lazyvals
+
+object LazyVals {
+    class LazyHolder {
+        lazy val value = 1
+    }
+}

bench-run/src/main/scala/dotty/tools/benchmarks/lazyvals/UninitializedAccess copy.scala

@@ -0,0 +1,29 @@
+package dotty.tools.benchmarks.lazyvals
+
+import org.openjdk.jmh.annotations._
+import LazyVals.LazyHolder
+import org.openjdk.jmh.infra.Blackhole
+import java.util.concurrent.TimeUnit
+
+@BenchmarkMode(Array(Mode.AverageTime))
+@Fork(2)
+@Threads(1)
+@Warmup(iterations = 5)
+@Measurement(iterations = 5)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@State(Scope.Benchmark)
+class UninitializedAccess {
+
+    var holder: LazyHolder = _
+
+    @Setup
+    def prepare: Unit = {
+      holder = new LazyHolder
+    }
+
+    @Benchmark
+    def measureInitialized(bh: Blackhole) = {
+      bh.consume(holder)
+      bh.consume(holder.value)
+    }
+}

community-build/community-projects/scala-parallel-collections

@@ -7,6 +7,7 @@ import Types._, Contexts._, Flags._
 import Symbols._, Annotations._, Trees._, Symbols._, Constants.Constant
 import Decorators._
 import dotty.tools.dotc.transform.SymUtils._
+import transform.LazyVals
 
 /** A map that applies three functions and a substitution together to a tree and
  *  makes sure they are coordinated so that the result is well-typed. The functions are

compiler/src/dotty/tools/dotc/ast/TreeTypeMap.scala

@@ -241,6 +241,7 @@ private sealed trait XSettings:
   val XcheckMacros: Setting[Boolean] = BooleanSetting("-Xcheck-macros", "Check some invariants of macro generated code while expanding macros", aliases = List("--Xcheck-macros"))
   val XmainClass: Setting[String] = StringSetting("-Xmain-class", "path", "Class for manifest's Main-Class entry (only useful with -d <jar>)", "")
   val XimplicitSearchLimit: Setting[Int] = IntSetting("-Ximplicit-search-limit", "Maximal number of expressions to be generated in an implicit search", 50000)
+  val XlegacyLazyVals: Setting[Boolean] = BooleanSetting("-Xlegacy-lazy-values", "Use legacy lazy vals implementations")
 
   val XmixinForceForwarders = ChoiceSetting(
     name    = "-Xmixin-force-forwarders",