SI-6969, mishandling of SoftReferences in method cache.

More interesting to test than it was to fix. The soft
reference is now dereferenced once, the locally stored
underlying value ascertained to be non-null, and the
remainder of the references to the value use the local var.

The enclosed test reliably NPEs without this patch.

2 files changed, 29 insertions, 0 deletions

diff --git a/test/files/run/t6969.check b/test/files/run/t6969.check
new file mode 100644
index 0000000000..78297812c9
--- /dev/null
+++ b/test/files/run/t6969.check
@@ -0,0 +1 @@
+All threads completed.
diff --git a/test/files/run/t6969.scala b/test/files/run/t6969.scala
new file mode 100644
index 0000000000..8cfc28c1e5
--- /dev/null
+++ b/test/files/run/t6969.scala
@@ -0,0 +1,28 @@
+object Test {
+  private type Clearable = { def clear(): Unit }
+  private def choke() = {
+    try new Array[Object]((Runtime.getRuntime().maxMemory min Int.MaxValue).toInt)
+    catch {
+      case _: OutOfMemoryError => // what do you mean, out of memory?
+      case t: Throwable        => println(t)
+    }
+  }
+  private def f(x: Clearable) = x.clear()
+  class Choker(id: Int) extends Thread {
+    private def g(iteration: Int) = {
+      val map = scala.collection.mutable.Map[Int, Int](1 -> 2)
+      try f(map) catch { case t: NullPointerException => println(s"Failed at $id/$iteration") ; throw t }
+      choke()
+    }
+    override def run() {
+      1 to 50 foreach g
+    }
+  }
+
+  def main(args: Array[String]): Unit = {
+    val threads = 1 to 3 map (id => new Choker(id))
+    threads foreach (_.start())
+    threads foreach (_.join())
+    println("All threads completed.")
+  }
+}