merge: Increase minimum Java version to 17 (#115)

This pull request increases the minimum version of Java required by OpenDC to 17.
This new version of Java introduces several new features compared to our old minimum 
version (11), which we attempt to apply in this conversion.

## Implementation Notes :hammer_and_pick:

* Increase minimum Java version to Java 17 
* Use RandomGenerator as randomness source 
* Add common dispatcher interface 
* Add compatibility with Kotlin coroutines
* Use InstantSource as time source
* Re-implement SimulationScheduler as Dispatcher 
* Replace use of CoroutineContext by Dispatcher 

## External Dependencies :four_leaf_clover:

* Java 17

## Breaking API Changes :warning:

* The use of `CoroutineContext` and `Clock` as parameters of classes has been replaced 
  by the `Dispatcher` interface.
* The use of `Clock` has been replaced by `InstantSource` which does not carry time
   zone info.
* The use of `Random` and `SplittableRandom` as parameter type has been replaced 
   by `RandomGenerator`

7 files changed, 36 insertions, 15 deletions

diff --git a/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/SimHost.kt b/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/SimHost.kt
index 5eccc6ec..a44ccc27 100644
--- a/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/SimHost.kt
+++ b/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/SimHost.kt
@@ -45,9 +45,9 @@ import org.opendc.simulator.compute.model.ProcessingNode
 import org.opendc.simulator.compute.model.ProcessingUnit
 import org.opendc.simulator.compute.workload.SimWorkload
 import org.opendc.simulator.compute.workload.SimWorkloads
-import java.time.Clock
 import java.time.Duration
 import java.time.Instant
+import java.time.InstantSource
 import java.util.UUID
 import java.util.function.Supplier
 
@@ -68,7 +68,7 @@ public class SimHost(
     override val uid: UUID,
     override val name: String,
     override val meta: Map<String, Any>,
-    private val clock: Clock,
+    private val clock: InstantSource,
     private val machine: SimBareMetalMachine,
     private val hypervisor: SimHypervisor,
     private val mapper: SimWorkloadMapper = DefaultWorkloadMapper,
diff --git a/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/failure/HostFault.kt b/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/failure/HostFault.kt
index 258ccc89..d34f70d7 100644
--- a/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/failure/HostFault.kt
+++ b/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/failure/HostFault.kt
@@ -23,7 +23,7 @@
 package org.opendc.compute.simulator.failure
 
 import org.opendc.compute.simulator.SimHost
-import java.time.Clock
+import java.time.InstantSource
 
 /**
  * Interface responsible for applying the fault to a host.
@@ -32,5 +32,5 @@ public interface HostFault {
     /**
      * Apply the fault to the specified [victims].
      */
-    public suspend fun apply(clock: Clock, victims: List<SimHost>)
+    public suspend fun apply(clock: InstantSource, victims: List<SimHost>)
 }
diff --git a/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/failure/HostFaultInjector.kt b/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/failure/HostFaultInjector.kt
index 5eff439f..afbb99d2 100644
--- a/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/failure/HostFaultInjector.kt
+++ b/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/failure/HostFaultInjector.kt
@@ -26,6 +26,7 @@ import org.apache.commons.math3.distribution.RealDistribution
 import org.opendc.compute.simulator.SimHost
 import org.opendc.compute.simulator.internal.HostFaultInjectorImpl
 import java.time.Clock
+import java.time.InstantSource
 import kotlin.coroutines.CoroutineContext
 
 /**
@@ -55,7 +56,7 @@ public interface HostFaultInjector : AutoCloseable {
          */
         public operator fun invoke(
             context: CoroutineContext,
-            clock: Clock,
+            clock: InstantSource,
             hosts: Set<SimHost>,
             iat: RealDistribution,
             selector: VictimSelector,
diff --git a/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/failure/StartStopHostFault.kt b/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/failure/StartStopHostFault.kt
index fc7cebfc..8bd25391 100644
--- a/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/failure/StartStopHostFault.kt
+++ b/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/failure/StartStopHostFault.kt
@@ -25,14 +25,14 @@ package org.opendc.compute.simulator.failure
 import kotlinx.coroutines.delay
 import org.apache.commons.math3.distribution.RealDistribution
 import org.opendc.compute.simulator.SimHost
-import java.time.Clock
+import java.time.InstantSource
 import kotlin.math.roundToLong
 
 /**
  * A type of [HostFault] where the hosts are stopped and recover after some random amount of time.
  */
 public class StartStopHostFault(private val duration: RealDistribution) : HostFault {
-    override suspend fun apply(clock: Clock, victims: List<SimHost>) {
+    override suspend fun apply(clock: InstantSource, victims: List<SimHost>) {
         for (host in victims) {
             host.fail()
         }
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/main/kotlin/org/opendc/compute/simulator/internal/Guest.kt b/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/internal/Guest.kt
index ca947625..02766cb1 100644
--- a/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/internal/Guest.kt
+++ b/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/internal/Guest.kt
@@ -32,15 +32,15 @@ import org.opendc.compute.simulator.SimWorkloadMapper
 import org.opendc.simulator.compute.SimMachineContext
 import org.opendc.simulator.compute.kernel.SimHypervisor
 import org.opendc.simulator.compute.kernel.SimVirtualMachine
-import java.time.Clock
 import java.time.Duration
 import java.time.Instant
+import java.time.InstantSource
 
 /**
  * A virtual machine instance that is managed by a [SimHost].
  */
 internal class Guest(
-    private val clock: Clock,
+    private val clock: InstantSource,
     val host: SimHost,
     private val hypervisor: SimHypervisor,
     private val mapper: SimWorkloadMapper,
diff --git a/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/internal/HostFaultInjectorImpl.kt b/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/internal/HostFaultInjectorImpl.kt
index f03bffe9..afc0b0d4 100644
--- a/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/internal/HostFaultInjectorImpl.kt
+++ b/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/internal/HostFaultInjectorImpl.kt
@@ -32,7 +32,7 @@ import org.opendc.compute.simulator.SimHost
 import org.opendc.compute.simulator.failure.HostFault
 import org.opendc.compute.simulator.failure.HostFaultInjector
 import org.opendc.compute.simulator.failure.VictimSelector
-import java.time.Clock
+import java.time.InstantSource
 import kotlin.coroutines.CoroutineContext
 import kotlin.math.roundToLong
 
@@ -40,7 +40,7 @@ import kotlin.math.roundToLong
  * Internal implementation of the [HostFaultInjector] interface.
  *
  * @param context The scope to run the fault injector in.
- * @param clock The [Clock] to keep track of simulation time.
+ * @param clock The [InstantSource] to keep track of simulation time.
  * @param hosts The set of hosts to inject faults into.
  * @param iat The inter-arrival time distribution of the failures (in hours).
  * @param selector The [VictimSelector] to select the host victims.
@@ -48,7 +48,7 @@ import kotlin.math.roundToLong
  */
 internal class HostFaultInjectorImpl(
     private val context: CoroutineContext,
-    private val clock: Clock,
+    private val clock: InstantSource,
     private val hosts: Set<SimHost>,
     private val iat: RealDistribution,
     private val selector: VictimSelector,