Do not interrupt LARS at shutdown or tasks might fail. See #3005

akka-actor-tests/src/test/scala/akka/actor/SchedulerSpec.scala

@@ -7,7 +7,7 @@ package akka.actor
 import language.postfixOps
 import java.io.Closeable
 import java.util.concurrent._
-import java.util.concurrent.atomic.AtomicInteger
+import atomic.{ AtomicReference, AtomicInteger }
 import scala.concurrent.{ future, Await, ExecutionContext }
 import scala.concurrent.duration._
 import scala.concurrent.forkjoin.ThreadLocalRandom
@@ -475,7 +475,7 @@ class LightArrayRevolverSchedulerSpec extends AkkaSpec(SchedulerSpec.testConfRev
 
   def withScheduler(start: Long = 0L, config: Config = ConfigFactory.empty)(thunk: (Scheduler with Closeable, Driver) ⇒ Unit): Unit = {
     import akka.actor.{ LightArrayRevolverScheduler ⇒ LARS }
-    val lbq = new LinkedBlockingQueue[Long]
+    val lbq = new AtomicReference[LinkedBlockingQueue[Long]](new LinkedBlockingQueue[Long])
     val prb = TestProbe()
     val tf = system.asInstanceOf[ActorSystemImpl].threadFactory
     val sched =
@@ -487,14 +487,30 @@ class LightArrayRevolverSchedulerSpec extends AkkaSpec(SchedulerSpec.testConfRev
         override protected def waitNanos(ns: Long): Unit = {
           // println(s"waiting $ns")
           prb.ref ! ns
-          try time += lbq.take()
+          try time += (lbq.get match {
+            case q: LinkedBlockingQueue[Long] ⇒ q.take()
+            case _ ⇒
+              val start = System.nanoTime()
+              super.waitNanos(ns)
+              System.nanoTime() - start
+          })
           catch {
             case _: InterruptedException ⇒ Thread.currentThread.interrupt()
           }
         }
+        override def close(): Unit = {
+          lbq.getAndSet(null) match {
+            case q: LinkedBlockingQueue[Long] ⇒ q.offer(0L)
+            case _                            ⇒
+          }
+          super.close()
+        }
       }
     val driver = new Driver {
-      def wakeUp(d: FiniteDuration) { lbq.offer(d.toNanos) }
+      def wakeUp(d: FiniteDuration) = lbq.get match {
+        case q: LinkedBlockingQueue[Long] ⇒ q.offer(d.toNanos)
+        case _                            ⇒
+      }
       def expectWait(): FiniteDuration = probe.expectMsgType[Long].nanos
       def probe = prb
       def step = sched.TickDuration

akka-actor/src/main/resources/reference.conf

@@ -363,6 +363,9 @@ akka {
     # If you are scheduling a lot of tasks you should consider increasing the
     # ticks per wheel.
     # For more information see: http://www.jboss.org/netty/
+    # Note that it might take up to 1 tick to stop the Timer, so setting the
+    # tick-duration to a high value will make shutting down the actor system
+    # take longer.
     tick-duration = 100ms
     
     # The timer uses a circular wheel of buckets to store the timer tasks.

akka-actor/src/main/scala/akka/actor/Scheduler.scala

@@ -342,7 +342,10 @@ class LightArrayRevolverScheduler(config: Config,
   private val stopped = new AtomicReference[Promise[immutable.Seq[TimerTask]]]
   def stop(): Future[immutable.Seq[TimerTask]] =
     if (stopped.compareAndSet(null, Promise())) {
-      timerThread.interrupt()
+      // Interrupting the timer thread to make it shut down faster is not good since
+      // it could be in the middle of executing the scheduled tasks, which might not
+      // respond well to being interrupted.
+      // Instead we just wait one more tick for it to finish.
       stopped.get.future
     } else Future.successful(Nil)