fixed overflow in exponential backoff RetryStrategy

Author: Roman Janusz

commons-core/src/main/scala/com/avsystem/commons/concurrent/RetryStrategy.scala

@@ -1,7 +1,7 @@
 package com.avsystem.commons
 package concurrent
 
-import scala.concurrent.duration.{Duration, FiniteDuration}
+import scala.concurrent.duration._
 
 /**
   * A `RetryStrategy` is conceptually a lazy sequence of delays, possibly infinite.
@@ -84,10 +84,10 @@ object RetryStrategy {
     apply(Opt((delay, continually(delay))))
 
   def exponentially(firstDelay: FiniteDuration, factor: Double = 2): RetryStrategy = apply {
-    val nextStrat = firstDelay * factor match {
-      case fd: FiniteDuration => exponentially(fd, factor)
-      case _ => never
-    }
+    val nextNanos = firstDelay.toNanos * factor
+    val nextStrat =
+      if (nextNanos > Long.MaxValue) continually(Long.MaxValue.nanos)
+      else exponentially(nextNanos.nanos, factor)
     Opt((firstDelay, nextStrat))
   }
 }

commons-core/src/test/scala/com/avsystem/commons/concurrent/ExponentialBackoffTest.scala

@@ -13,11 +13,18 @@ import scala.concurrent.duration._
 class ExponentialBackoffTest extends AnyFunSuite with Matchers {
   test("simple") {
     import RetryStrategy._
-    val eb = immediately.andThen(exponentially(1.second)).maxDelay(20.seconds).maxRetries(8)
+    val eb = immediately.andThen(exponentially(1.second)).maxDelay(20.seconds).maxRetries(64)
 
     val allDelays = Iterator.iterateUntilEmpty(eb.nextRetry)(_._2.nextRetry).map(_._1).toList
     allDelays shouldBe List(
-      Duration.Zero, 1.second, 2.seconds, 4.seconds, 8.seconds, 16.seconds, 20.seconds, 20.seconds
+      Duration.Zero, 1.second, 2.seconds, 4.seconds, 8.seconds, 16.seconds, 20.seconds, 20.seconds,
+      20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds,
+      20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds,
+      20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds,
+      20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds,
+      20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds,
+      20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds,
+      20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds, 20.seconds,
     )
   }
 }