Merge pull request scala#10793 from EnzeXing/Predef-Vector-cycle

Fixing initialization cycle between object `Predef` and `Vector`

Author: lrytz

src/library/scala/collection/immutable/Vector.scala

@@ -81,8 +81,9 @@ object Vector extends StrictOptimizedSeqFactory[Vector] {
   }
 
   private val defaultApplyPreferredMaxLength: Int =
-    try System.getProperty("scala.collection.immutable.Vector.defaultApplyPreferredMaxLength",
-      "250").toInt
+    // explicit StringOps to avoid initialization cycle with Predef (scala/bug#13009)
+    try new StringOps(System.getProperty("scala.collection.immutable.Vector.defaultApplyPreferredMaxLength",
+      "250")).toInt
     catch {
       case _: SecurityException => 250
     }

test/files/run/deadlock.scala

@@ -0,0 +1,18 @@
+object Test extends App {
+  val createPredef = new Runnable {
+    def run = {
+      val _ = Predef;
+    }
+  }
+  val createVector = new Runnable {
+    def run = {
+      val _ = scala.collection.immutable.Vector;
+    }
+  }
+  val t1 = new Thread(createPredef)
+  val t2 = new Thread(createVector)
+  t1.start()
+  t2.start()
+  t1.join()
+  t2.join()
+}