LazyListIterableBase for Scala.js

Author: lrytz

library-js/src/scala/collection/immutable/LazyListIterableBase.scala

@@ -0,0 +1,54 @@
+/*
+ * Scala (https://www.scala-lang.org)
+ *
+ * Copyright EPFL and Lightbend, Inc. dba Akka
+ *
+ * Licensed under Apache License 2.0
+ * (http://www.apache.org/licenses/LICENSE-2.0).
+ *
+ * See the NOTICE file distributed with this work for
+ * additional information regarding copyright ownership.
+ */
+
+package scala.collection.immutable
+
+import scala.language.`2.13`
+import language.experimental.captureChecking
+
+/**
+ * Base class for [[LazyList]] to split out code that uses concurrency utilities that are not available on Scala.js.
+ */
+abstract class LazyListIterableBase[+A] private[immutable] (initialTail: (AnyRef | Null)^) extends Iterable[A] with Serializable {
+  /** See [[LazyList._head]] for the possible states of this field. */
+  @volatile private var _tail: AnyRef^{this} | Null /* () => LazyList[A] | Thread | InRace | LazyList[A] | Null */ =
+    caps.unsafe.unsafeAssumePure(initialTail)
+
+  private[immutable] def rawTail: AnyRef^{this} | Null = _tail
+
+  private[immutable] def setRawTail(value: AnyRef^): Unit = _tail = caps.unsafe.unsafeAssumePure(value)
+
+  private[immutable] def makeTailUpdater: LazyListIterableBase.TailUpdater = LazyListIterableBase.TailUpdater()
+}
+
+private[immutable] object LazyListIterableBase {
+  import caps.unsafe.unsafeAssumePure
+
+  final class TailUpdater {
+    @inline def compareAndSet(ll: LazyListIterableBase[?]^, expected: AnyRef^, value: AnyRef^): Boolean =
+      if (ll._tail eq expected) { ll._tail = unsafeAssumePure(value); true } else false
+    @inline def getAndSet(ll: LazyListIterableBase[?]^, value: (AnyRef | Null)^): (AnyRef | Null)^ = {
+      val old = ll._tail
+      ll._tail = value.asInstanceOf[AnyRef | Null]
+      old
+    }
+  }
+
+  def isCurrentThread(t: Thread^): Boolean = true
+
+  def InRace(t: Thread^): InRace = throw new Exception("unreachable")
+
+  final class InRace private[LazyListIterableBase] (val owner: Thread) {
+    def await(): Unit = ()
+    def countDown(): Unit = ()
+  }
+}