1 files changed, 103 insertions, 0 deletions
diff --git a/library/src/dotty/runtime/LazyVals.scala b/library/src/dotty/runtime/LazyVals.scala
new file mode 100644
index 000000000..4dea0d34d
--- /dev/null
+++ b/library/src/dotty/runtime/LazyVals.scala
@@ -0,0 +1,103 @@
+package dotty.runtime
+
+import scala.annotation.tailrec
+
+/**
+ * Helper methods used in thread-safe lazy vals.
+ */
+object LazyVals {
+  private val unsafe = scala.concurrent.util.Unsafe.instance
+
+  final val BITS_PER_LAZY_VAL = 2L
+  final val LAZY_VAL_MASK = 3L
+  final val debug = false
+
+  @inline def STATE(cur: Long, ord: Int) = {
+    val r = (cur >> (ord * BITS_PER_LAZY_VAL)) & LAZY_VAL_MASK
+    if (debug)
+      println(s"STATE($cur, $ord) = $r")
+    r
+  }
+  @inline def CAS(t: Object, offset: Long, e: Long, v: Int, ord: Int) = {
+    if (debug)
+      println(s"CAS($t, $offset, $e, $v, $ord)")
+    val mask = ~(LAZY_VAL_MASK << ord * BITS_PER_LAZY_VAL)
+    val n = (e & mask) | (v << (ord * BITS_PER_LAZY_VAL))
+    compareAndSet(t, offset, e, n)
+  }
+  @inline def setFlag(t: Object, offset: Long, v: Int, ord: Int) = {
+    if (debug)
+      println(s"setFlag($t, $offset, $v, $ord)")
+    var retry = true
+    while (retry) {
+      val cur = get(t, offset)
+      if (STATE(cur, ord) == 1) retry = CAS(t, offset, cur, v, ord)
+      else {
+        // cur == 2, somebody is waiting on monitor
+        if (CAS(t, offset, cur, v, ord)) {
+          val monitor = getMonitor(t, ord)
+          monitor.synchronized {
+            monitor.notifyAll()
+          }
+          retry = false
+        }
+      }
+    }
+  }
+  @inline def wait4Notification(t: Object, offset: Long, cur: Long, ord: Int) = {
+    if (debug)
+      println(s"wait4Notification($t, $offset, $cur, $ord)")
+    var retry = true
+    while (retry) {
+      val cur = get(t, offset)
+      val state = STATE(cur, ord)
+      if (state == 1) CAS(t, offset, cur, 2, ord)
+      else if (state == 2) {
+        val monitor = getMonitor(t, ord)
+        monitor.synchronized {
+          monitor.wait()
+        }
+      }
+      else retry = false
+    }
+  }
+
+  @inline def compareAndSet(t: Object, off: Long, e: Long, v: Long) = unsafe.compareAndSwapLong(t, off, e, v)
+  @inline def get(t: Object, off: Long) = {
+    if (debug)
+      println(s"get($t, $off)")
+    unsafe.getLongVolatile(t, off)
+  }
+
+  val processors: Int = java.lang.Runtime.getRuntime.availableProcessors()
+  val base: Int = 8 * processors * processors
+  val monitors: Array[Object] = (0 to base).map {
+    x => new Object()
+  }.toArray
+
+  @inline def getMonitor(obj: Object, fieldId: Int = 0) = {
+    var id = (
+      /*java.lang.System.identityHashCode(obj) + */ // should be here, but #548
+      fieldId) % base
+
+    if (id < 0) id += base
+    monitors(id)
+  }
+
+  @inline def getOffset(clz: Class[_], name: String) = {
+    val r = unsafe.objectFieldOffset(clz.getDeclaredField(name))
+    if (debug)
+      println(s"getOffset($clz, $name) = $r")
+    r
+  }
+
+  object Names {
+    final val state = "STATE"
+    final val cas = "CAS"
+    final val setFlag = "setFlag"
+    final val wait4Notification = "wait4Notification"
+    final val compareAndSet = "compareAndSet"
+    final val get = "get"
+    final val getOffset = "getOffset"
+  }
+}