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* The use of `CoroutineContext` and `Clock` as parameters of classes has been replaced 
  by the `Dispatcher` interface.
* The use of `Clock` has been replaced by `InstantSource` which does not carry time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* The use of `Random` and `SplittableRandom` as parameter type has been replaced 
   by `RandomGenerator`

4 files changed, 14 insertions, 19 deletions

diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/ComputeService.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/ComputeService.kt
index 85222c10..9d7dcba6 100644
--- a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/ComputeService.kt
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/ComputeService.kt
@@ -22,15 +22,14 @@
 
 package org.opendc.compute.service
 
+import org.opendc.common.Dispatcher
 import org.opendc.compute.api.ComputeClient
 import org.opendc.compute.api.Server
 import org.opendc.compute.service.driver.Host
 import org.opendc.compute.service.internal.ComputeServiceImpl
 import org.opendc.compute.service.scheduler.ComputeScheduler
 import org.opendc.compute.service.telemetry.SchedulerStats
-import java.time.Clock
 import java.time.Duration
-import kotlin.coroutines.CoroutineContext
 
 /**
  * The [ComputeService] hosts the API implementation of the OpenDC Compute service.
@@ -80,18 +79,16 @@ public interface ComputeService : AutoCloseable {
         /**
          * Construct a new [ComputeService] implementation.
          *
-         * @param context The [CoroutineContext] to use in the service.
-         * @param clock The clock instance to use.
+         * @param dispatcher The [Dispatcher] for scheduling future events.
          * @param scheduler The scheduler implementation to use.
          * @param schedulingQuantum The interval between scheduling cycles.
          */
         public operator fun invoke(
-            context: CoroutineContext,
-            clock: Clock,
+            dispatcher: Dispatcher,
             scheduler: ComputeScheduler,
             schedulingQuantum: Duration = Duration.ofMinutes(5)
         ): ComputeService {
-            return ComputeServiceImpl(context, clock, scheduler, schedulingQuantum)
+            return ComputeServiceImpl(dispatcher, scheduler, schedulingQuantum)
         }
     }
 }
diff --git a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/internal/ComputeServiceImpl.kt b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/internal/ComputeServiceImpl.kt
index b377c3e3..77932545 100644
--- a/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/internal/ComputeServiceImpl.kt
+++ b/opendc-compute/opendc-compute-service/src/main/kotlin/org/opendc/compute/service/internal/ComputeServiceImpl.kt
@@ -23,6 +23,7 @@
 package org.opendc.compute.service.internal
 
 import mu.KotlinLogging
+import org.opendc.common.Dispatcher
 import org.opendc.common.util.Pacer
 import org.opendc.compute.api.ComputeClient
 import org.opendc.compute.api.Flavor
@@ -35,27 +36,23 @@ import org.opendc.compute.service.driver.HostListener
 import org.opendc.compute.service.driver.HostState
 import org.opendc.compute.service.scheduler.ComputeScheduler
 import org.opendc.compute.service.telemetry.SchedulerStats
-import java.time.Clock
 import java.time.Duration
 import java.time.Instant
 import java.util.ArrayDeque
 import java.util.Deque
 import java.util.Random
 import java.util.UUID
-import kotlin.coroutines.CoroutineContext
 import kotlin.math.max
 
 /**
  * Internal implementation of the OpenDC Compute service.
  *
- * @param coroutineContext The [CoroutineContext] to use in the service.
- * @param clock The clock instance to use.
+ * @param dispatcher The [Dispatcher] for scheduling future events.
  * @param scheduler The scheduler implementation to use.
  * @param schedulingQuantum The interval between scheduling cycles.
  */
 internal class ComputeServiceImpl(
-    coroutineContext: CoroutineContext,
-    private val clock: Clock,
+    private val dispatcher: Dispatcher,
     private val scheduler: ComputeScheduler,
     schedulingQuantum: Duration
 ) : ComputeService, HostListener {
@@ -108,6 +105,7 @@ internal class ComputeServiceImpl(
     override val hosts: Set<Host>
         get() = hostToView.keys
 
+    private val clock = dispatcher.timeSource
     private var maxCores = 0
     private var maxMemory = 0L
     private var _attemptsSuccess = 0L
@@ -120,7 +118,7 @@ internal class ComputeServiceImpl(
     /**
      * The [Pacer] to use for scheduling the scheduler cycles.
      */
-    private val pacer = Pacer(coroutineContext, clock, schedulingQuantum.toMillis()) { doSchedule() }
+    private val pacer = Pacer(dispatcher, schedulingQuantum.toMillis()) { doSchedule() }
 
     override fun newClient(): ComputeClient {
         check(!isClosed) { "Service is already closed" }
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-service/src/test/kotlin/org/opendc/compute/service/ComputeServiceTest.kt b/opendc-compute/opendc-compute-service/src/test/kotlin/org/opendc/compute/service/ComputeServiceTest.kt
index c18709f3..b5685aba 100644
--- a/opendc-compute/opendc-compute-service/src/test/kotlin/org/opendc/compute/service/ComputeServiceTest.kt
+++ b/opendc-compute/opendc-compute-service/src/test/kotlin/org/opendc/compute/service/ComputeServiceTest.kt
@@ -62,12 +62,11 @@ internal class ComputeServiceTest {
     @BeforeEach
     fun setUp() {
         scope = SimulationCoroutineScope()
-        val clock = scope.clock
         val computeScheduler = FilterScheduler(
             filters = listOf(ComputeFilter(), VCpuFilter(allocationRatio = 1.0), RamFilter(allocationRatio = 1.0)),
             weighers = listOf(RamWeigher())
         )
-        service = ComputeService(scope.coroutineContext, clock, computeScheduler)
+        service = ComputeService(scope.dispatcher, computeScheduler)
     }
 
     @Test