Merge pull request #56 from isaacl/addThreadLocalSecure

Add TestableRandom and ThreadLocalSecureRandom

lila/src/main/scala/Random.scala

@@ -1,29 +1,44 @@
 package scalalib
 
 object ThreadLocalRandom extends RandomApi:
-  protected[scalalib] def impl = java.util.concurrent.ThreadLocalRandom.current()
+  protected def impl = java.util.concurrent.ThreadLocalRandom.current()
 
+/** Thread-safe, but the underlying impl, [[java.security.SecureRandom]], uses synchronized methods, which has
+  * degraded performance under high contention. See [[ThreadLocalSecureRandom]].
+  */
 object SecureRandom extends RandomApi:
   protected val impl = java.security.SecureRandom.getInstanceStrong()
 
-private abstract class RandomApi:
+/** An alternative to [[SecureRandom]] which offers improved performance under high contention.
+  */
+object ThreadLocalSecureRandom extends RandomApi:
+  private val store = new java.lang.ThreadLocal[java.util.Random]:
+    override def initialValue = java.security.SecureRandom.getInstanceStrong()
+  protected def impl = store.get
+
+/** A deterministic random number generator for testing purposes.
+  */
+final class TestableRandom(seed: Long) extends RandomApi:
+  protected val impl = new java.util.Random(seed)
+
+sealed abstract class RandomApi:
   protected def impl: java.util.Random
 
-  def nextBoolean()     = impl.nextBoolean
-  def nextDouble()      = impl.nextDouble
-  def nextFloat()       = impl.nextFloat
-  def nextGaussian()    = impl.nextGaussian
-  def nextInt()         = impl.nextInt
-  def nextInt(n: Int)   = impl.nextInt(n)
-  def nextLong()        = impl.nextLong
-  def nextLong(l: Long) = impl.nextLong(l)
+  final def nextBoolean()     = impl.nextBoolean
+  final def nextDouble()      = impl.nextDouble
+  final def nextFloat()       = impl.nextFloat
+  final def nextGaussian()    = impl.nextGaussian
+  final def nextInt()         = impl.nextInt
+  final def nextInt(n: Int)   = impl.nextInt(n)
+  final def nextLong()        = impl.nextLong
+  final def nextLong(l: Long) = impl.nextLong(l)
 
-  def nextBytes(len: Int): Array[Byte] =
+  final def nextBytes(len: Int): Array[Byte] =
     val bytes = new Array[Byte](len)
     impl.nextBytes(bytes)
     bytes
 
-  def nextString(len: Int): String =
+  final def nextString(len: Int): String =
     val randomImpl = impl
     val chars      = RandomApi.chars
     val arr        = new Array[Char](len)
@@ -34,17 +49,17 @@ private abstract class RandomApi:
       i += 1
     String.valueOf(arr)
 
-  def shuffle[T, C](xs: IterableOnce[T])(using scala.collection.BuildFrom[xs.type, T, C]): C =
+  final def shuffle[T, C](xs: IterableOnce[T])(using scala.collection.BuildFrom[xs.type, T, C]): C =
     scala.util.Random(impl).shuffle(xs)
 
-  def oneOf[A](seq: scala.collection.IndexedSeq[A]): Option[A] =
+  final def oneOf[A](seq: scala.collection.IndexedSeq[A]): Option[A] =
     val len = seq.length
     if len > 0 then Some(seq(impl.nextInt(len))) else None
 
   // odds(1) = 100% true
   // odds(2) = 50% true
   // odds(3) = 33% true
-  def odds(n: Int): Boolean = impl.nextFloat() * n < 1
+  final def odds(n: Int): Boolean = impl.nextFloat() * n < 1f
 
 private object RandomApi:
   // private vals are accessed directly as a static field.