refactor: Use RandomGenerator as randomness source

This change updates the modules of OpenDC to always accept
the `RandomGenerator` interface as source of randomness. This interface
is implemented by the slower `java.util.Random` class, but also by the
faster `java.util.SplittableRandom` class

3 files changed, 28 insertions, 7 deletions

diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/FilterScheduler.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/FilterScheduler.kt
index 233f5ef6..0840ba7e 100644
--- a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/FilterScheduler.kt
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/scheduler/FilterScheduler.kt
@@ -26,7 +26,8 @@ import org.opendc.compute.api.Server
 import org.opendc.compute.service.internal.HostView
 import org.opendc.compute.service.scheduler.filters.HostFilter
 import org.opendc.compute.service.scheduler.weights.HostWeigher
-import java.util.Random
+import java.util.SplittableRandom
+import java.util.random.RandomGenerator
 import kotlin.math.min
 
 /**
@@ -39,13 +40,13 @@ import kotlin.math.min
  * @param filters The list of filters to apply when searching for an appropriate host.
  * @param weighers The list of weighers to apply when searching for an appropriate host.
  * @param subsetSize The size of the subset of best hosts from which a target is randomly chosen.
- * @param random A [Random] instance for selecting
+ * @param random A [RandomGenerator] instance for selecting
  */
 public class FilterScheduler(
     private val filters: List<HostFilter>,
     private val weighers: List<HostWeigher>,
     private val subsetSize: Int = 1,
-    private val random: Random = Random(0)
+    private val random: RandomGenerator = SplittableRandom(0)
 ) : ComputeScheduler {
     /**
      * The pool of hosts available to the scheduler.
diff --git a/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/failure/StochasticVictimSelector.kt b/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/failure/StochasticVictimSelector.kt
index b6d466bd..4aba0e91 100644
--- a/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/failure/StochasticVictimSelector.kt
+++ b/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/failure/StochasticVictimSelector.kt
@@ -24,7 +24,9 @@ package org.opendc.compute.simulator.failure
 
 import org.apache.commons.math3.distribution.RealDistribution
 import org.opendc.compute.simulator.SimHost
-import java.util.Random
+import java.util.ArrayList
+import java.util.SplittableRandom
+import java.util.random.RandomGenerator
 import kotlin.math.roundToInt
 
 /**
@@ -32,12 +34,30 @@ import kotlin.math.roundToInt
  */
 public class StochasticVictimSelector(
     private val size: RealDistribution,
-    private val random: Random = Random(0)
+    private val random: RandomGenerator = SplittableRandom(0)
 ) : VictimSelector {
 
     override fun select(hosts: Set<SimHost>): List<SimHost> {
         val n = size.sample().roundToInt()
-        return hosts.shuffled(random).take(n)
+        val result = ArrayList<SimHost>(n)
+
+        val random = random
+        var samplesNeeded = n
+        var remainingHosts = hosts.size
+        val iterator = hosts.iterator()
+
+        while (iterator.hasNext() && samplesNeeded > 0) {
+            val host = iterator.next()
+
+            if (random.nextInt(remainingHosts) < samplesNeeded) {
+                result.add(host)
+                samplesNeeded--
+            }
+
+            remainingHosts--
+        }
+
+        return result
     }
 
     override fun toString(): String = "StochasticVictimSelector[$size]"
diff --git a/opendc-compute/opendc-compute-simulator/src/test/kotlin/org/opendc/compute/simulator/failure/HostFaultInjectorTest.kt b/opendc-compute/opendc-compute-simulator/src/test/kotlin/org/opendc/compute/simulator/failure/HostFaultInjectorTest.kt
index 90f534e6..a65c37cf 100644
--- a/opendc-compute/opendc-compute-simulator/src/test/kotlin/org/opendc/compute/simulator/failure/HostFaultInjectorTest.kt
+++ b/opendc-compute/opendc-compute-simulator/src/test/kotlin/org/opendc/compute/simulator/failure/HostFaultInjectorTest.kt
@@ -38,7 +38,7 @@ import kotlin.math.ln
 /**
  * Test suite for [HostFaultInjector] class.
  */
-internal class HostFaultInjectorTest {
+class HostFaultInjectorTest {
     /**
      * Simple test case to test that nothing happens when the injector is not started.
      */