Use nanoTime in FixedRateTask, see #2214

* Rewrote test to use latch and assert rate instead

akka-cluster/src/main/scala/akka/cluster/FixedRateTask.scala

@@ -29,11 +29,10 @@ private[akka] object FixedRateTask {
  */
 private[akka] class FixedRateTask(scheduler: Scheduler, initalDelay: Duration, delay: Duration, task: Runnable) extends Runnable {
 
-  private val delayMillis = delay.toMillis
-  private val minDelayMillis = 1L
+  private val delayNanos = delay.toNanos
   private val cancelled = new AtomicBoolean(false)
   private val counter = new AtomicLong(0L)
-  private val startTime = System.currentTimeMillis + initalDelay.toMillis
+  private val startTime = System.nanoTime + initalDelay.toNanos
   scheduler.scheduleOnce(initalDelay, this)
 
   def cancel(): Unit = cancelled.set(true)
@@ -41,11 +40,9 @@ private[akka] class FixedRateTask(scheduler: Scheduler, initalDelay: Duration, d
   override final def run(): Unit = if (!cancelled.get) try {
     task.run()
   } finally if (!cancelled.get) {
-    val nextTime = startTime + delayMillis * counter.incrementAndGet
-    val nextDelayMillis = nextTime - System.currentTimeMillis
-    val nextDelay = Duration(
-      (if (nextDelayMillis <= minDelayMillis) minDelayMillis else nextDelayMillis),
-      TimeUnit.MILLISECONDS)
+    val nextTime = startTime + delayNanos * counter.incrementAndGet
+    // it's ok to schedule with negative duration, will run asap
+    val nextDelay = Duration(nextTime - System.nanoTime, TimeUnit.NANOSECONDS)
     try {
       scheduler.scheduleOnce(nextDelay, this)
     } catch { case e: IllegalStateException ⇒ /* will happen when scheduler is closed, nothing wrong */ }

akka-cluster/src/test/scala/akka/cluster/FixedRateTaskSpec.scala

@@ -4,32 +4,39 @@
 
 package akka.cluster
 
-import java.util.concurrent.atomic.AtomicInteger
 import akka.testkit.AkkaSpec
 import akka.util.duration._
 import akka.testkit.TimingTest
+import akka.testkit.TestLatch
+import akka.dispatch.Await
 
 @org.junit.runner.RunWith(classOf[org.scalatest.junit.JUnitRunner])
 class FixedRateTaskSpec extends AkkaSpec {
 
   "Task scheduled at fixed rate" must {
     "adjust for scheduler inaccuracy" taggedAs TimingTest in {
-      val counter = new AtomicInteger
+      val startTime = System.nanoTime
+      val n = 33
+      val latch = new TestLatch(n)
       FixedRateTask(system.scheduler, 150.millis, 150.millis) {
-        counter.incrementAndGet()
+        latch.countDown()
       }
-      5000.millis.sleep()
-      counter.get must (be(33) or be(34))
+      Await.ready(latch, 6.seconds)
+      val rate = n * 1000.0 / (System.nanoTime - startTime).nanos.toMillis
+      rate must be(6.66 plusOrMinus (0.4))
     }
 
     "compensate for long running task" taggedAs TimingTest in {
-      val counter = new AtomicInteger
+      val startTime = System.nanoTime
+      val n = 22
+      val latch = new TestLatch(n)
       FixedRateTask(system.scheduler, 225.millis, 225.millis) {
-        counter.incrementAndGet()
         80.millis.sleep()
+        latch.countDown()
       }
-      5000.millis.sleep()
-      counter.get must (be(22) or be(23))
+      Await.ready(latch, 6.seconds)
+      val rate = n * 1000.0 / (System.nanoTime - startTime).nanos.toMillis
+      rate must be(4.4 plusOrMinus (0.3))
     }
   }
 }