Fixes memory leak when using reflection

References to Threads would be retained long after their termination if
reflection is used in them. This led to a steady, long memory leak in
applications using reflection in thread pools.

1 files changed, 29 insertions, 0 deletions

diff --git a/test/files/run/t8946.scala b/test/files/run/t8946.scala
new file mode 100644
index 0000000000..a248a20501
--- /dev/null
+++ b/test/files/run/t8946.scala
@@ -0,0 +1,29 @@
+// Tests to assert that references to threads are not strongly held when scala-reflection is used inside of them.
+object Test {
+  import scala.ref.WeakReference
+
+  def forceGc() = {
+    var obj = new Object
+    val ref = new WeakReference(obj)
+    obj = null;
+    while(ref.get.nonEmpty)
+      Array.ofDim[Byte](16 * 1024 * 1024)
+  }
+
+  def main(args: Array[String]): Unit = {
+    val threads = for (i <- (1 to 16)) yield {
+      val t = new Thread {
+        override def run(): Unit = {
+          import reflect.runtime.universe._
+          typeOf[List[String]] <:< typeOf[Seq[_]]
+        }
+      }
+      t.start()
+      t.join()
+      WeakReference(t)
+    }
+    forceGc()
+    val nonGCdThreads = threads.filter(_.get.nonEmpty).length
+    assert(nonGCdThreads == 0, s"${nonGCdThreads} threads were retained; expected 0.")
+  }
+}