Adds test and caps the timeout check period to 1s #24616

akka-stream-tests/src/test/scala/akka/stream/impl/TimeoutsSpec.scala

@@ -4,12 +4,15 @@
 
 package akka.stream.impl
 
-import java.util.concurrent.TimeoutException
+import java.util.concurrent.{ TimeUnit, TimeoutException }
+
 import akka.Done
 import akka.stream.scaladsl._
 import akka.stream.testkit.Utils._
 import akka.stream.testkit.{ StreamSpec, TestPublisher, TestSubscriber }
 import akka.stream._
+import org.scalatest.{ Matchers, WordSpecLike }
+
 import scala.concurrent.duration._
 import scala.concurrent.{ Await, Future }
 
@@ -354,3 +357,24 @@ class TimeoutsSpec extends StreamSpec {
   }
 
 }
+
+class TimeoutChecksSpec extends WordSpecLike with Matchers {
+
+  "Timeout check interval" must {
+    import scala.concurrent.duration.{ Duration, FiniteDuration }
+
+    "run twice for timeouts under 800ms" in {
+      Timers.timeoutCheckInterval(800.millis) should ===(100.millis)
+    }
+
+    "run every 8th of the value for timeouts for timeouts under 1s" in {
+      Timers.timeoutCheckInterval(999.millis).toNanos should ===(999.millis.toNanos / 8)
+    }
+
+    "run every 1s for timeouts over 1s" in {
+      Timers.timeoutCheckInterval(1001.millis) should ===(1.second)
+    }
+
+  }
+
+}

akka-stream/src/main/scala/akka/stream/impl/Timers.scala

@@ -25,11 +25,17 @@ import scala.concurrent.duration.{ Duration, FiniteDuration }
  *  - otherwise, these streams do not interfere with the element flow, ordinary completion or failure
  */
 @InternalApi private[akka] object Timers {
-  private def idleTimeoutCheckInterval(timeout: FiniteDuration): FiniteDuration = {
+
+  /**
+   * Given a timeout computes how often the check should be run without causing
+   * excessive load or loosing timeout precision.
+   */
+  private[akka] def timeoutCheckInterval(timeout: FiniteDuration): FiniteDuration = {
     import scala.concurrent.duration._
-    FiniteDuration(
-      math.min(math.max(timeout.toNanos / 8, 100.millis.toNanos), timeout.toNanos / 2),
-      TimeUnit.NANOSECONDS)
+    if (timeout > 1.second) 1.second
+    else {
+      FiniteDuration(math.min(math.max(timeout.toNanos / 8, 100.millis.toNanos), timeout.toNanos / 2), TimeUnit.NANOSECONDS)
+    }
   }
 
   final class Initial[T](val timeout: FiniteDuration) extends SimpleLinearGraphStage[T] {
@@ -100,7 +106,7 @@ import scala.concurrent.duration.{ Duration, FiniteDuration }
           if (nextDeadline - System.nanoTime < 0)
             failStage(new TimeoutException(s"No elements passed in the last $timeout."))
 
-        override def preStart(): Unit = schedulePeriodically(GraphStageLogicTimer, idleTimeoutCheckInterval(timeout))
+        override def preStart(): Unit = schedulePeriodically(GraphStageLogicTimer, timeoutCheckInterval(timeout))
       }
 
     override def toString = "IdleTimeout"
@@ -132,7 +138,7 @@ import scala.concurrent.duration.{ Duration, FiniteDuration }
           if (waitingDemand && (nextDeadline - System.nanoTime < 0))
             failStage(new TimeoutException(s"No demand signalled in the last $timeout."))
 
-        override def preStart(): Unit = schedulePeriodically(GraphStageLogicTimer, idleTimeoutCheckInterval(timeout))
+        override def preStart(): Unit = schedulePeriodically(GraphStageLogicTimer, timeoutCheckInterval(timeout))
       }
 
     override def toString = "BackpressureTimeout"
@@ -160,13 +166,14 @@ import scala.concurrent.duration.{ Duration, FiniteDuration }
         if (nextDeadline - System.nanoTime < 0)
           failStage(new TimeoutException(s"No elements passed in the last $timeout."))
 
-      override def preStart(): Unit = schedulePeriodically(GraphStageLogicTimer, idleTimeoutCheckInterval(timeout))
+      override def preStart(): Unit = schedulePeriodically(GraphStageLogicTimer, timeoutCheckInterval(timeout))
 
       class IdleBidiHandler[P](in: Inlet[P], out: Outlet[P]) extends InHandler with OutHandler {
         override def onPush(): Unit = {
           onActivity()
           push(out, grab(in))
         }
+
         override def onPull(): Unit = pull(in)
         override def onUpstreamFinish(): Unit = complete(out)
         override def onDownstreamFinish(): Unit = cancel(in)