Use `ThreadLocalRandom` in `TrieMap.size`.

2 files changed, 12 insertions, 5 deletions

diff --git a/src/library/scala/collection/concurrent/TrieMap.scala b/src/library/scala/collection/concurrent/TrieMap.scala
index 08e9125bd8..2d8217551a 100644
--- a/src/library/scala/collection/concurrent/TrieMap.scala
+++ b/src/library/scala/collection/concurrent/TrieMap.scala
@@ -473,7 +473,11 @@ extends CNodeBase[K, V] {
   private def computeSize(ct: TrieMap[K, V]): Int = {
     var i = 0
     var sz = 0
-    val offset = math.abs(util.Random.nextInt()) % array.length
+    val offset =
+      if (array.length > 0)
+        //util.Random.nextInt(array.length) /* <-- benchmarks show that this causes observable contention */
+        scala.concurrent.forkjoin.ThreadLocalRandom.current.nextInt(0, array.length)
+      else 0
     while (i < array.length) {
       val pos = (i + offset) % array.length
       array(pos) match {
diff --git a/test/benchmarking/ParCtrie-size.scala b/test/benchmarking/ParCtrie-size.scala
index 5a6191fb62..3f47dc23fd 100644
--- a/test/benchmarking/ParCtrie-size.scala
+++ b/test/benchmarking/ParCtrie-size.scala
@@ -2,16 +2,18 @@
 
 
 
-import collection.parallel.mutable.ParCtrie
+import collection.parallel.mutable.ParTrieMap
 
 
 
 object Size extends testing.Benchmark {
   val length = sys.props("length").toInt
   val par = sys.props("par").toInt
-  var parctrie = ParCtrie((0 until length) zip (0 until length): _*)
+  var parctrie = ParTrieMap((0 until length) zip (0 until length): _*)
   
-  collection.parallel.ForkJoinTasks.defaultForkJoinPool.setParallelism(par)
+  //collection.parallel.ForkJoinTasks.defaultForkJoinPool.setParallelism(par)
+  val ts = new collection.parallel.ForkJoinTaskSupport(new concurrent.forkjoin.ForkJoinPool(par))
+  parctrie.tasksupport = ts
   
   def run = {
     parctrie.size
@@ -21,7 +23,8 @@ object Size extends testing.Benchmark {
   
   override def tearDown() {
     iteration += 1
-    if (iteration % 4 == 0) parctrie = ParCtrie((0 until length) zip (0 until length): _*)
+    if (iteration % 4 == 0) parctrie = ParTrieMap((0 until length) zip (0 until length): _*)
+    parctrie.tasksupport = ts
   }
   
 }