merge: Simplify usage of ComputeMetricExporter

This pull request addresses some issues with the current implementation of 
the `ComputeMetricExporter` class. 
In particular, the construction of `ComputeMetricExporter` does not require a `Clock` anymore.

- Ensure shutdown of exporter is called 
- Do not require clock for ComputeMetricExporter
- Do not recover guests in non-error state
- Write null values explicitly in Parquet exporter
- Report cause of compute exporter failure

**Breaking API Changes**

- `ComputeMetricExporter` is now an abstract class that can be extended to collect metrics
- `ParquetComputeMonitor` has been renamed to `ParquetComputeMetricExporter` and extends `ComputeMetricExporter`

3 files changed, 8 insertions, 8 deletions

diff --git a/opendc-compute/opendc-compute-workload/src/main/kotlin/org/opendc/compute/workload/export/parquet/ParquetExportMonitor.kt b/opendc-compute/opendc-compute-workload/src/main/kotlin/org/opendc/compute/workload/export/parquet/ParquetComputeMetricExporter.kt
index f41a2241..ad182d67 100644
--- a/opendc-compute/opendc-compute-workload/src/main/kotlin/org/opendc/compute/workload/export/parquet/ParquetExportMonitor.kt
+++ b/opendc-compute/opendc-compute-workload/src/main/kotlin/org/opendc/compute/workload/export/parquet/ParquetComputeMetricExporter.kt
@@ -22,6 +22,8 @@
 
 package org.opendc.compute.workload.export.parquet
 
+import io.opentelemetry.sdk.common.CompletableResultCode
+import org.opendc.telemetry.compute.ComputeMetricExporter
 import org.opendc.telemetry.compute.ComputeMonitor
 import org.opendc.telemetry.compute.table.HostData
 import org.opendc.telemetry.compute.table.ServerData
@@ -31,7 +33,7 @@ import java.io.File
 /**
  * A [ComputeMonitor] that logs the events to a Parquet file.
  */
-public class ParquetExportMonitor(base: File, partition: String, bufferSize: Int) : ComputeMonitor, AutoCloseable {
+public class ParquetComputeMetricExporter(base: File, partition: String, bufferSize: Int) : ComputeMetricExporter() {
     private val serverWriter = ParquetServerDataWriter(
         File(base, "server/$partition/data.parquet").also { it.parentFile.mkdirs() },
         bufferSize
@@ -59,9 +61,11 @@ public class ParquetExportMonitor(base: File, partition: String, bufferSize: Int
         serviceWriter.write(data)
     }
 
-    override fun close() {
+    override fun shutdown(): CompletableResultCode {
         hostWriter.close()
         serviceWriter.close()
         serverWriter.close()
+
+        return CompletableResultCode.ofSuccess()
     }
 }
diff --git a/opendc-compute/opendc-compute-workload/src/main/kotlin/org/opendc/compute/workload/export/parquet/ParquetHostDataWriter.kt b/opendc-compute/opendc-compute-workload/src/main/kotlin/org/opendc/compute/workload/export/parquet/ParquetHostDataWriter.kt
index 37066a0d..98a0739e 100644
--- a/opendc-compute/opendc-compute-workload/src/main/kotlin/org/opendc/compute/workload/export/parquet/ParquetHostDataWriter.kt
+++ b/opendc-compute/opendc-compute-workload/src/main/kotlin/org/opendc/compute/workload/export/parquet/ParquetHostDataWriter.kt
@@ -54,9 +54,7 @@ public class ParquetHostDataWriter(path: File, bufferSize: Int) :
         builder["uptime"] = data.uptime
         builder["downtime"] = data.downtime
         val bootTime = data.bootTime
-        if (bootTime != null) {
-            builder["boot_time"] = bootTime.toEpochMilli()
-        }
+        builder["boot_time"] = bootTime?.toEpochMilli()
 
         builder["cpu_count"] = data.host.cpuCount
         builder["cpu_limit"] = data.cpuLimit
diff --git a/opendc-compute/opendc-compute-workload/src/main/kotlin/org/opendc/compute/workload/export/parquet/ParquetServerDataWriter.kt b/opendc-compute/opendc-compute-workload/src/main/kotlin/org/opendc/compute/workload/export/parquet/ParquetServerDataWriter.kt
index bea23d32..0d11ec23 100644
--- a/opendc-compute/opendc-compute-workload/src/main/kotlin/org/opendc/compute/workload/export/parquet/ParquetServerDataWriter.kt
+++ b/opendc-compute/opendc-compute-workload/src/main/kotlin/org/opendc/compute/workload/export/parquet/ParquetServerDataWriter.kt
@@ -56,9 +56,7 @@ public class ParquetServerDataWriter(path: File, bufferSize: Int) :
         builder["uptime"] = data.uptime
         builder["downtime"] = data.downtime
         val bootTime = data.bootTime
-        if (bootTime != null) {
-            builder["boot_time"] = bootTime.toEpochMilli()
-        }
+        builder["boot_time"] = bootTime?.toEpochMilli()
         builder["scheduling_latency"] = data.schedulingLatency
 
         builder["cpu_count"] = data.server.cpuCount