merge: Address technical debt in codebase

This pull request removes some of the existing technical debt in the OpenDC codebase.

Close #51

## Implementation Notes :hammer_and_pick:

* Add Pacer to pace scheduling cycles.
* Rename utils module to common module
* Optimize TimerScheduler
* Remove opendc-platform module
* Disallow duplicate UIDs for SimHost

## Breaking API Changes :warning:

* TimerScheduler does not implement `AutoCloseable` anymore.

4 files changed, 7 insertions, 36 deletions

diff --git a/opendc-workflow/opendc-workflow-api/build.gradle.kts b/opendc-workflow/opendc-workflow-api/build.gradle.kts
index 36239d05..03569d8c 100644
--- a/opendc-workflow/opendc-workflow-api/build.gradle.kts
+++ b/opendc-workflow/opendc-workflow-api/build.gradle.kts
@@ -28,7 +28,6 @@ plugins {
 }
 
 dependencies {
-    api(platform(projects.opendcPlatform))
     api(projects.opendcCompute.opendcComputeApi)
     implementation(libs.kotlin.logging)
 }
diff --git a/opendc-workflow/opendc-workflow-service/build.gradle.kts b/opendc-workflow/opendc-workflow-service/build.gradle.kts
index 4d8b7d7f..17df33e3 100644
--- a/opendc-workflow/opendc-workflow-service/build.gradle.kts
+++ b/opendc-workflow/opendc-workflow-service/build.gradle.kts
@@ -30,11 +30,10 @@ plugins {
 }
 
 dependencies {
-    api(platform(projects.opendcPlatform))
     api(projects.opendcWorkflow.opendcWorkflowApi)
     api(projects.opendcCompute.opendcComputeApi)
     api(projects.opendcTelemetry.opendcTelemetryApi)
-    implementation(projects.opendcUtils)
+    implementation(projects.opendcCommon)
     implementation(libs.kotlin.logging)
 
     testImplementation(projects.opendcWorkflow.opendcWorkflowWorkload)
diff --git a/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/internal/WorkflowServiceImpl.kt b/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/internal/WorkflowServiceImpl.kt
index 7b6d8651..cdaec021 100644
--- a/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/internal/WorkflowServiceImpl.kt
+++ b/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/internal/WorkflowServiceImpl.kt
@@ -25,8 +25,8 @@ package org.opendc.workflow.service.internal
 import io.opentelemetry.api.metrics.Meter
 import io.opentelemetry.api.metrics.MeterProvider
 import kotlinx.coroutines.*
+import org.opendc.common.util.Pacer
 import org.opendc.compute.api.*
-import org.opendc.utils.TimerScheduler
 import org.opendc.workflow.api.Job
 import org.opendc.workflow.api.WORKFLOW_TASK_CORES
 import org.opendc.workflow.service.*
@@ -187,9 +187,9 @@ public class WorkflowServiceImpl(
         .build()
 
     /**
-     * The [TimerScheduler] to use for scheduling the scheduler cycles.
+     * The [Pacer] to use for scheduling the scheduler cycles.
      */
-    private val timerScheduler: TimerScheduler<Unit> = TimerScheduler(scope.coroutineContext, clock)
+    private val pacer = Pacer(scope.coroutineContext, clock, schedulingQuantum.toMillis()) { doSchedule() }
 
     private val jobAdmissionPolicy: JobAdmissionPolicy.Logic
     private val taskEligibilityPolicy: TaskEligibilityPolicy.Logic
@@ -230,7 +230,7 @@ public class WorkflowServiceImpl(
         rootListener.jobSubmitted(jobInstance)
         submittedJobs.add(1)
 
-        requestSchedulingCycle()
+        pacer.enqueue()
     }
 
     override fun close() {
@@ -252,31 +252,6 @@ public class WorkflowServiceImpl(
     }
 
     /**
-     * Indicate that a new scheduling cycle is needed due to a change to the service's state.
-     */
-    private fun requestSchedulingCycle() {
-        // Bail out in case we have already requested a new cycle or the queue is empty.
-        if (timerScheduler.isTimerActive(Unit)) {
-            return
-        }
-
-        val quantum = schedulingQuantum.toMillis()
-        if (quantum == 0L) {
-            doSchedule()
-            return
-        }
-
-        // We assume that the provisioner runs at a fixed slot every time quantum (e.g t=0, t=60, t=120).
-        // This is important because the slices of the VMs need to be aligned.
-        // We calculate here the delay until the next scheduling slot.
-        val delay = quantum - (clock.millis() % quantum)
-
-        timerScheduler.startSingleTimer(Unit, delay) {
-            doSchedule()
-        }
-    }
-
-    /**
      * Perform a scheduling cycle immediately.
      */
     private fun doSchedule() {
@@ -409,10 +384,9 @@ public class WorkflowServiceImpl(
                     finishJob(job)
                 }
 
-                requestSchedulingCycle()
-            }
-            ServerState.DELETED -> {
+                pacer.enqueue()
             }
+            ServerState.DELETED -> {}
             else -> throw IllegalStateException()
         }
     }
diff --git a/opendc-workflow/opendc-workflow-workload/build.gradle.kts b/opendc-workflow/opendc-workflow-workload/build.gradle.kts
index dfb77a39..a9d497af 100644
--- a/opendc-workflow/opendc-workflow-workload/build.gradle.kts
+++ b/opendc-workflow/opendc-workflow-workload/build.gradle.kts
@@ -29,7 +29,6 @@ plugins {
 }
 
 dependencies {
-    api(platform(projects.opendcPlatform))
     api(projects.opendcWorkflow.opendcWorkflowService)
 
     implementation(projects.opendcSimulator.opendcSimulatorCompute)