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* The use of `CoroutineContext` and `Clock` as parameters of classes has been replaced 
  by the `Dispatcher` interface.
* The use of `Clock` has been replaced by `InstantSource` which does not carry time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* The use of `Random` and `SplittableRandom` as parameter type has been replaced 
   by `RandomGenerator`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, 22 insertions, 31 deletions

diff --git a/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/FaaSService.kt b/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/FaaSService.kt
index 7b40d867..96619cdb 100644
--- a/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/FaaSService.kt
+++ b/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/FaaSService.kt
@@ -22,6 +22,7 @@
 
 package org.opendc.faas.service
 
+import org.opendc.common.Dispatcher
 import org.opendc.faas.api.FaaSClient
 import org.opendc.faas.api.FaaSFunction
 import org.opendc.faas.service.autoscaler.FunctionTerminationPolicy
@@ -30,9 +31,7 @@ import org.opendc.faas.service.internal.FaaSServiceImpl
 import org.opendc.faas.service.router.RoutingPolicy
 import org.opendc.faas.service.telemetry.FunctionStats
 import org.opendc.faas.service.telemetry.SchedulerStats
-import java.time.Clock
 import java.time.Duration
-import kotlin.coroutines.CoroutineContext
 
 /**
  * The [FaaSService] hosts the service implementation of the OpenDC FaaS platform.
@@ -62,22 +61,20 @@ public interface FaaSService : AutoCloseable {
         /**
          * Construct a new [FaaSService] implementation.
          *
-         * @param context The [CoroutineContext] to use in the service.
-         * @param clock The clock instance to use.
+         * @param dispatcher The [Dispatcher] used for scheduling events.
          * @param deployer the [FunctionDeployer] to use for deploying function instances.
          * @param routingPolicy The policy to route function invocations.
          * @param terminationPolicy The policy for terminating function instances.
          * @param quantum The scheduling quantum of the service (100 ms default)
          */
         public operator fun invoke(
-            context: CoroutineContext,
-            clock: Clock,
+            dispatcher: Dispatcher,
             deployer: FunctionDeployer,
             routingPolicy: RoutingPolicy,
             terminationPolicy: FunctionTerminationPolicy,
             quantum: Duration = Duration.ofMillis(100)
         ): FaaSService {
-            return FaaSServiceImpl(context, clock, deployer, routingPolicy, terminationPolicy, quantum)
+            return FaaSServiceImpl(dispatcher, deployer, routingPolicy, terminationPolicy, quantum)
         }
     }
 }
diff --git a/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/autoscaler/FunctionTerminationPolicyFixed.kt b/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/autoscaler/FunctionTerminationPolicyFixed.kt
index d579ad0c..a2c371e1 100644
--- a/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/autoscaler/FunctionTerminationPolicyFixed.kt
+++ b/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/autoscaler/FunctionTerminationPolicyFixed.kt
@@ -22,12 +22,11 @@
 
 package org.opendc.faas.service.autoscaler
 
+import org.opendc.common.Dispatcher
 import org.opendc.common.util.TimerScheduler
 import org.opendc.faas.service.deployer.FunctionInstance
 import org.opendc.faas.service.deployer.FunctionInstanceState
-import java.time.Clock
 import java.time.Duration
-import kotlin.coroutines.CoroutineContext
 
 /**
  * A [FunctionTerminationPolicy] that terminates idle function instances after a fixed keep-alive time.
@@ -35,14 +34,13 @@ import kotlin.coroutines.CoroutineContext
  * @param timeout The idle timeout after which the function instance is terminated.
  */
 public class FunctionTerminationPolicyFixed(
-    context: CoroutineContext,
-    clock: Clock,
+    dispatcher: Dispatcher,
     public val timeout: Duration
 ) : FunctionTerminationPolicy {
     /**
      * The [TimerScheduler] used to schedule the function terminations.
      */
-    private val scheduler = TimerScheduler<FunctionInstance>(context, clock)
+    private val scheduler = TimerScheduler<FunctionInstance>(dispatcher)
 
     override fun enqueue(instance: FunctionInstance) {
         // Cancel the existing timeout timer
@@ -61,6 +59,6 @@ public class FunctionTerminationPolicyFixed(
      * Schedule termination for the specified [instance].
      */
     private fun schedule(instance: FunctionInstance) {
-        scheduler.startSingleTimer(instance, delay = timeout.toMillis()) { instance.close() }
+        scheduler.startSingleTimer(instance, timeout.toMillis()) { instance.close() }
     }
 }
diff --git a/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/internal/FaaSServiceImpl.kt b/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/internal/FaaSServiceImpl.kt
index 901213af..b1e6b3f5 100644
--- a/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/internal/FaaSServiceImpl.kt
+++ b/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/internal/FaaSServiceImpl.kt
@@ -22,13 +22,11 @@
 
 package org.opendc.faas.service.internal
 
-import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.InternalCoroutinesApi
-import kotlinx.coroutines.Job
-import kotlinx.coroutines.cancel
 import kotlinx.coroutines.intrinsics.startCoroutineCancellable
 import kotlinx.coroutines.suspendCancellableCoroutine
 import mu.KotlinLogging
+import org.opendc.common.Dispatcher
 import org.opendc.common.util.Pacer
 import org.opendc.faas.api.FaaSClient
 import org.opendc.faas.api.FaaSFunction
@@ -43,13 +41,12 @@ import org.opendc.faas.service.router.RoutingPolicy
 import org.opendc.faas.service.telemetry.FunctionStats
 import org.opendc.faas.service.telemetry.SchedulerStats
 import java.lang.IllegalStateException
-import java.time.Clock
 import java.time.Duration
+import java.time.InstantSource
 import java.util.ArrayDeque
 import java.util.Random
 import java.util.UUID
 import kotlin.coroutines.Continuation
-import kotlin.coroutines.CoroutineContext
 import kotlin.coroutines.resumeWithException
 
 /**
@@ -60,19 +57,13 @@ import kotlin.coroutines.resumeWithException
  * this component queues the events to await the deployment of new instances.
  */
 internal class FaaSServiceImpl(
-    context: CoroutineContext,
-    private val clock: Clock,
+    dispatcher: Dispatcher,
     private val deployer: FunctionDeployer,
     private val routingPolicy: RoutingPolicy,
     private val terminationPolicy: FunctionTerminationPolicy,
     quantum: Duration
 ) : FaaSService, FunctionInstanceListener {
     /**
-     * The [CoroutineScope] of the service bounded by the lifecycle of the service.
-     */
-    private val scope = CoroutineScope(context + Job())
-
-    /**
      * The logger instance of this server.
      */
     private val logger = KotlinLogging.logger {}
@@ -80,7 +71,12 @@ internal class FaaSServiceImpl(
     /**
      * The [Pacer] to use for scheduling the scheduler cycles.
      */
-    private val pacer = Pacer(scope.coroutineContext, clock, quantum = quantum.toMillis()) { doSchedule() }
+    private val pacer = Pacer(dispatcher, quantum.toMillis()) { doSchedule() }
+
+    /**
+     * The [InstantSource] instance representing the clock.
+     */
+    private val clock = dispatcher.timeSource
 
     /**
      * The [Random] instance used to generate unique identifiers for the objects.
@@ -266,8 +262,6 @@ internal class FaaSServiceImpl(
     }
 
     override fun close() {
-        scope.cancel()
-
         // Stop all function instances
         for ((_, function) in functions) {
             function.close()
diff --git a/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/router/RandomRoutingPolicy.kt b/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/router/RandomRoutingPolicy.kt
index 5bd9d4d3..22bf7266 100644
--- a/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/router/RandomRoutingPolicy.kt
+++ b/opendc-faas/opendc-faas-service/src/main/kotlin/org/opendc/faas/service/router/RandomRoutingPolicy.kt
@@ -24,13 +24,15 @@ package org.opendc.faas.service.router
 
 import org.opendc.faas.service.FunctionObject
 import org.opendc.faas.service.deployer.FunctionInstance
-import kotlin.random.Random
+import java.util.SplittableRandom
+import java.util.random.RandomGenerator
 
 /**
  * A [RoutingPolicy] that selects a random function instance.
  */
-public class RandomRoutingPolicy(private val random: Random = Random(0)) : RoutingPolicy {
+public class RandomRoutingPolicy(private val random: RandomGenerator = SplittableRandom(0)) : RoutingPolicy {
     override fun select(instances: List<FunctionInstance>, function: FunctionObject): FunctionInstance {
-        return instances.random(random)
+        val idx = random.nextInt(instances.size)
+        return instances.elementAt(idx)
     }
 }