Integrate OpenTelemetry into OpenDC

This pull request resolves issue #91 by adopting the industry-standard OpenTelemetry standard
for collecting traces and metrics in OpenDC simulations:

* Metrics will now be exposed through OpenTelemetry's metrics API
* `opendc-telemetry` provides complementary code to support
    gathering telemetry in OpenDC.

**Breaking API Changes**
* `opendc-tracer` has been removed.
* `EventFlow` and all usages of it have been removed.
* `opendc-experiments-sc18` has been removed for now, but a 
    suitable replacement will follow soon.

3 files changed, 94 insertions, 135 deletions

diff --git a/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/WorkflowEvent.kt b/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/WorkflowEvent.kt
deleted file mode 100644
index bb2ad6c6..00000000
--- a/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/WorkflowEvent.kt
+++ /dev/null
@@ -1,79 +0,0 @@
-/*
- * Copyright (c) 2021 AtLarge Research
- *
- * Permission is hereby granted, free of charge, to any person obtaining a copy
- * of this software and associated documentation files (the "Software"), to deal
- * in the Software without restriction, including without limitation the rights
- * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
- * copies of the Software, and to permit persons to whom the Software is
- * furnished to do so, subject to the following conditions:
- *
- * The above copyright notice and this permission notice shall be included in all
- * copies or substantial portions of the Software.
- *
- * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
- * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
- * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
- * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
- * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
- * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
- * SOFTWARE.
- */
-
-package org.opendc.workflow.service
-
-import org.opendc.trace.core.Event
-import org.opendc.workflow.api.Job
-import org.opendc.workflow.api.Task
-
-/**
- * An event emitted by the [WorkflowService].
- */
-public sealed class WorkflowEvent : Event() {
-    /**
-     * The [WorkflowService] that emitted the event.
-     */
-    public abstract val service: WorkflowService
-
-    /**
-     * This event is emitted when a job was submitted to the scheduler.
-     */
-    public data class JobSubmitted(
-        override val service: WorkflowService,
-        public val job: Job
-    ) : WorkflowEvent()
-
-    /**
-     * This event is emitted when a job has become active.
-     */
-    public data class JobStarted(
-        override val service: WorkflowService,
-        public val job: Job
-    ) : WorkflowEvent()
-
-    /**
-     * This event is emitted when a job has finished processing.
-     */
-    public data class JobFinished(
-        override val service: WorkflowService,
-        public val job: Job
-    ) : WorkflowEvent()
-
-    /**
-     * This event is emitted when a task of a job has started processing.
-     */
-    public data class TaskStarted(
-        override val service: WorkflowService,
-        public val job: Job,
-        public val task: Task
-    ) : WorkflowEvent()
-
-    /**
-     * This event is emitted when a task of a job has started processing.
-     */
-    public data class TaskFinished(
-        override val service: WorkflowService,
-        public val job: Job,
-        public val task: Task
-    ) : WorkflowEvent()
-}
diff --git a/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/WorkflowService.kt b/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/WorkflowService.kt
index 2f83e376..d3358ef1 100644
--- a/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/WorkflowService.kt
+++ b/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/WorkflowService.kt
@@ -22,9 +22,8 @@
 
 package org.opendc.workflow.service
 
-import kotlinx.coroutines.flow.Flow
+import io.opentelemetry.api.metrics.Meter
 import org.opendc.compute.api.ComputeClient
-import org.opendc.trace.core.EventTracer
 import org.opendc.workflow.api.Job
 import org.opendc.workflow.service.internal.WorkflowServiceImpl
 import org.opendc.workflow.service.scheduler.WorkflowSchedulerMode
@@ -42,14 +41,14 @@ import kotlin.coroutines.CoroutineContext
  */
 public interface WorkflowService : AutoCloseable {
     /**
-     * The events emitted by the workflow scheduler.
+     * Submit the specified [Job] to the workflow service for scheduling.
      */
-    public val events: Flow<WorkflowEvent>
+    public suspend fun submit(job: Job)
 
     /**
-     * Submit the specified [Job] to the workflow service for scheduling.
+     * Run the specified [Job] and suspend execution until the job is finished.
      */
-    public suspend fun submit(job: Job)
+    public suspend fun run(job: Job)
 
     /**
      * Terminate the lifecycle of the workflow service, stopping all running workflows.
@@ -63,6 +62,7 @@ public interface WorkflowService : AutoCloseable {
          * @param context The [CoroutineContext] to use in the service.
          * @param clock The clock instance to use.
          * @param tracer The event tracer to use.
+         * @param meter The meter to use.
          * @param compute The compute client to use.
          * @param mode The scheduling mode to use.
          * @param jobAdmissionPolicy The job admission policy to use.
@@ -73,7 +73,7 @@ public interface WorkflowService : AutoCloseable {
         public operator fun invoke(
             context: CoroutineContext,
             clock: Clock,
-            tracer: EventTracer,
+            meter: Meter,
             compute: ComputeClient,
             mode: WorkflowSchedulerMode,
             jobAdmissionPolicy: JobAdmissionPolicy,
@@ -84,7 +84,7 @@ public interface WorkflowService : AutoCloseable {
             return WorkflowServiceImpl(
                 context,
                 clock,
-                tracer,
+                meter,
                 compute,
                 mode,
                 jobAdmissionPolicy,
diff --git a/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/internal/WorkflowServiceImpl.kt b/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/internal/WorkflowServiceImpl.kt
index 85a88acd..32191b8f 100644
--- a/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/internal/WorkflowServiceImpl.kt
+++ b/simulator/opendc-workflow/opendc-workflow-service/src/main/kotlin/org/opendc/workflow/service/internal/WorkflowServiceImpl.kt
@@ -22,17 +22,11 @@
 
 package org.opendc.workflow.service.internal
 
-import kotlinx.coroutines.CoroutineScope
-import kotlinx.coroutines.ExperimentalCoroutinesApi
-import kotlinx.coroutines.cancel
-import kotlinx.coroutines.flow.Flow
+import io.opentelemetry.api.metrics.Meter
+import kotlinx.coroutines.*
 import kotlinx.coroutines.flow.map
-import kotlinx.coroutines.launch
 import mu.KotlinLogging
 import org.opendc.compute.api.*
-import org.opendc.trace.core.EventTracer
-import org.opendc.trace.core.consumeAsFlow
-import org.opendc.trace.core.enable
 import org.opendc.workflow.api.Job
 import org.opendc.workflow.api.WORKFLOW_TASK_CORES
 import org.opendc.workflow.service.*
@@ -43,7 +37,9 @@ import org.opendc.workflow.service.scheduler.task.TaskEligibilityPolicy
 import org.opendc.workflow.service.scheduler.task.TaskOrderPolicy
 import java.time.Clock
 import java.util.*
+import kotlin.coroutines.Continuation
 import kotlin.coroutines.CoroutineContext
+import kotlin.coroutines.resume
 
 /**
  * A [WorkflowService] that distributes work through a multi-stage process based on the Reference Architecture for
@@ -52,7 +48,7 @@ import kotlin.coroutines.CoroutineContext
 public class WorkflowServiceImpl(
     context: CoroutineContext,
     internal val clock: Clock,
-    internal val tracer: EventTracer,
+    private val meter: Meter,
     private val computeClient: ComputeClient,
     mode: WorkflowSchedulerMode,
     jobAdmissionPolicy: JobAdmissionPolicy,
@@ -63,7 +59,7 @@ public class WorkflowServiceImpl(
     /**
      * The [CoroutineScope] of the service bounded by the lifecycle of the service.
      */
-    internal val scope = CoroutineScope(context)
+    internal val scope = CoroutineScope(context + Job())
 
     /**
      * The logger instance to use.
@@ -106,6 +102,11 @@ public class WorkflowServiceImpl(
     internal val taskByServer = mutableMapOf<Server, TaskState>()
 
     /**
+     * The continuation of the jobs.
+     */
+    private val conts = mutableMapOf<Job, Continuation<Unit>>()
+
+    /**
      * The root listener of this scheduler.
      */
     private val rootListener = object : WorkflowSchedulerListener {
@@ -151,6 +152,54 @@ public class WorkflowServiceImpl(
         }
     }
 
+    /**
+     * The number of jobs that have been submitted to the service.
+     */
+    private val submittedJobs = meter.longCounterBuilder("jobs.submitted")
+        .setDescription("Number of submitted jobs")
+        .setUnit("1")
+        .build()
+
+    /**
+     * The number of jobs that are running.
+     */
+    private val runningJobs = meter.longUpDownCounterBuilder("jobs.active")
+        .setDescription("Number of jobs running")
+        .setUnit("1")
+        .build()
+
+    /**
+     * The number of jobs that have finished running.
+     */
+    private val finishedJobs = meter.longCounterBuilder("jobs.finished")
+        .setDescription("Number of jobs that finished running")
+        .setUnit("1")
+        .build()
+
+    /**
+     * The number of tasks that have been submitted to the service.
+     */
+    private val submittedTasks = meter.longCounterBuilder("tasks.submitted")
+        .setDescription("Number of submitted tasks")
+        .setUnit("1")
+        .build()
+
+    /**
+     * The number of jobs that are running.
+     */
+    private val runningTasks = meter.longUpDownCounterBuilder("tasks.active")
+        .setDescription("Number of tasks running")
+        .setUnit("1")
+        .build()
+
+    /**
+     * The number of jobs that have finished running.
+     */
+    private val finishedTasks = meter.longCounterBuilder("tasks.finished")
+        .setDescription("Number of tasks that finished running")
+        .setUnit("1")
+        .build()
+
     private val mode: WorkflowSchedulerMode.Logic
     private val jobAdmissionPolicy: JobAdmissionPolicy.Logic
     private val taskEligibilityPolicy: TaskEligibilityPolicy.Logic
@@ -167,16 +216,7 @@ public class WorkflowServiceImpl(
         }
     }
 
-    override val events: Flow<WorkflowEvent> = tracer.openRecording().let {
-        it.enable<WorkflowEvent.JobSubmitted>()
-        it.enable<WorkflowEvent.JobStarted>()
-        it.enable<WorkflowEvent.JobFinished>()
-        it.enable<WorkflowEvent.TaskStarted>()
-        it.enable<WorkflowEvent.TaskFinished>()
-        it.consumeAsFlow().map { event -> event as WorkflowEvent }
-    }
-
-    override suspend fun submit(job: Job) {
+    override suspend fun run(job: Job) {
         // J1 Incoming Jobs
         val jobInstance = JobState(job, clock.millis())
         val instances = job.tasks.associateWith {
@@ -193,14 +233,24 @@ public class WorkflowServiceImpl(
             if (instance.isRoot) {
                 instance.state = TaskStatus.READY
             }
+
+            submittedTasks.add(1)
         }
 
-        instances.values.toCollection(jobInstance.tasks)
-        incomingJobs += jobInstance
-        rootListener.jobSubmitted(jobInstance)
-        tracer.commit(WorkflowEvent.JobSubmitted(this, jobInstance.job))
+        return suspendCancellableCoroutine { cont ->
+            instances.values.toCollection(jobInstance.tasks)
+            incomingJobs += jobInstance
+            rootListener.jobSubmitted(jobInstance)
+            conts[job] = cont
+
+            submittedJobs.add(1)
+
+            requestCycle()
+        }
+    }
 
-        requestCycle()
+    override suspend fun submit(job: Job) {
+        scope.launch { run(job) }
     }
 
     override fun close() {
@@ -231,12 +281,8 @@ public class WorkflowServiceImpl(
             iterator.remove()
             jobQueue.add(jobInstance)
             activeJobs += jobInstance
-            tracer.commit(
-                WorkflowEvent.JobStarted(
-                    this,
-                    jobInstance.job
-                )
-            )
+
+            runningJobs.add(1)
             rootListener.jobStarted(jobInstance)
         }
 
@@ -311,18 +357,11 @@ public class WorkflowServiceImpl(
 
     public override fun onStateChanged(server: Server, newState: ServerState) {
         when (newState) {
-            ServerState.PROVISIONING -> {
-            }
+            ServerState.PROVISIONING -> {}
             ServerState.RUNNING -> {
                 val task = taskByServer.getValue(server)
                 task.startedAt = clock.millis()
-                tracer.commit(
-                    WorkflowEvent.TaskStarted(
-                        this@WorkflowServiceImpl,
-                        task.job.job,
-                        task.task
-                    )
-                )
+                runningTasks.add(1)
                 rootListener.taskStarted(task)
             }
             ServerState.TERMINATED, ServerState.ERROR -> {
@@ -338,13 +377,9 @@ public class WorkflowServiceImpl(
                 task.finishedAt = clock.millis()
                 job.tasks.remove(task)
                 activeTasks -= task
-                tracer.commit(
-                    WorkflowEvent.TaskFinished(
-                        this@WorkflowServiceImpl,
-                        task.job.job,
-                        task.task
-                    )
-                )
+
+                runningTasks.add(-1)
+                finishedTasks.add(1)
                 rootListener.taskFinished(task)
 
                 // Add job roots to the scheduling queue
@@ -371,8 +406,11 @@ public class WorkflowServiceImpl(
 
     private fun finishJob(job: JobState) {
         activeJobs -= job
-        tracer.commit(WorkflowEvent.JobFinished(this, job.job))
+        runningJobs.add(-1)
+        finishedJobs.add(1)
         rootListener.jobFinished(job)
+
+        conts.remove(job.job)?.resume(Unit)
     }
 
     public fun addListener(listener: WorkflowSchedulerListener) {