Fixed SI-6505. Respond to ask calls by immediate failure even after c…

…ompiler shutdown.

When the compiler is asked to shutdown, it may still have items on the working queue, and more can be added by clients in other thread that don't *know* the compiler is down yet. These requests were never serviced, leading to deadlocks or timeouts.

review by @odersky, @hubertp

src/compiler/scala/tools/nsc/interactive/CompilerControl.scala

@@ -13,6 +13,7 @@ import scala.tools.nsc.util.FailedInterrupt
 import scala.tools.nsc.util.EmptyAction
 import scala.tools.nsc.util.WorkScheduler
 import scala.reflect.internal.util.{SourceFile, Position}
+import scala.tools.nsc.util.InterruptReq
 
 /** Interface of interactive compiler to a client such as an IDE
  *  The model the presentation compiler consists of the following parts:
@@ -413,6 +414,16 @@ trait CompilerControl { self: Global =>
     override def doQuickly[A](op: () => A): A = {
       throw new FailedInterrupt(new Exception("Posted a work item to a compiler that's shutting down"))
     }
+
+    override def askDoQuickly[A](op: () => A): InterruptReq { type R = A } = {
+      val ir = new InterruptReq {
+        type R = A
+        val todo = () => throw new MissingResponse
+      }
+      ir.execute()
+      ir
+    }
+
   }
 
 }

src/compiler/scala/tools/nsc/util/InterruptReq.scala

@@ -47,7 +47,10 @@ abstract class InterruptReq {
   }
 
   def onComplete(k: Continuation) = synchronized {
-    waiting = k :: waiting
+    if (result.isDefined)
+      k(result.get)
+    else
+      waiting = k :: waiting
   }
 }
 

test/files/presentation/forgotten-ask.scala

@@ -0,0 +1,33 @@
+import scala.tools.nsc.interactive._
+import tests._
+
+/** Test that no ask calls are left unanswered after a compiler has shut down. */
+object Test extends InteractiveTest {
+  import compiler._
+
+  def askItem(): Response[Unit] = {
+    compiler.askForResponse { () =>
+      Thread.sleep(100)
+    }
+  }
+
+  final val Timeout = 5000 //ms
+
+  override def main(args: Array[String]) {
+    val item1 = askItem()
+
+    compiler.askShutdown()
+
+    Thread.sleep(1000) // wait a bit, the compiler is shutting down
+    val item2 = askItem()
+
+    item1.get(Timeout) match {
+      case None => println("TIMEOUT")
+      case _ =>
+    }
+    item2.get(Timeout) match {
+      case None => println("TIMEOUT")
+      case _ =>
+    }
+  }
+}