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.

4 files changed, 20 insertions, 4 deletions

diff --git a/simulator/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/SimAbstractMachine.kt b/simulator/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/SimAbstractMachine.kt
index 1c0f94fd..2127b066 100644
--- a/simulator/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/SimAbstractMachine.kt
+++ b/simulator/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/SimAbstractMachine.kt
@@ -108,8 +108,11 @@ public abstract class SimAbstractMachine(private val clock: Clock) : SimMachine
                 .launchIn(this)
 
             launch {
-                source.consume(consumer)
-                job.cancel()
+                try {
+                    source.consume(consumer)
+                } finally {
+                    job.cancel()
+                }
             }
         }
     }
diff --git a/simulator/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/SimBareMetalMachine.kt b/simulator/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/SimBareMetalMachine.kt
index f86c4198..830ff70e 100644
--- a/simulator/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/SimBareMetalMachine.kt
+++ b/simulator/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/SimBareMetalMachine.kt
@@ -71,6 +71,7 @@ public class SimBareMetalMachine(
 
     override fun close() {
         super.close()
+
         scheduler.close()
         scope.cancel()
     }
diff --git a/simulator/opendc-simulator/opendc-simulator-resources/src/jmh/kotlin/org/opendc/simulator/resources/SimResourceBenchmarks.kt b/simulator/opendc-simulator/opendc-simulator-resources/src/jmh/kotlin/org/opendc/simulator/resources/SimResourceBenchmarks.kt
index 937b6966..f2eea97c 100644
--- a/simulator/opendc-simulator/opendc-simulator-resources/src/jmh/kotlin/org/opendc/simulator/resources/SimResourceBenchmarks.kt
+++ b/simulator/opendc-simulator/opendc-simulator-resources/src/jmh/kotlin/org/opendc/simulator/resources/SimResourceBenchmarks.kt
@@ -71,7 +71,7 @@ class SimResourceBenchmarks {
     fun benchmarkForwardOverhead(state: Workload) {
         return scope.runBlockingTest {
             val provider = SimResourceSource(4200.0, clock, scheduler)
-            val forwarder = SimResourceTransformer()
+            val forwarder = SimResourceForwarder()
             provider.startConsumer(forwarder)
             return@runBlockingTest forwarder.consume(state.consumers[0])
         }
diff --git a/simulator/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimAbstractResourceContext.kt b/simulator/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimAbstractResourceContext.kt
index 9705bd17..5c5ee038 100644
--- a/simulator/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimAbstractResourceContext.kt
+++ b/simulator/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimAbstractResourceContext.kt
@@ -54,8 +54,17 @@ public abstract class SimAbstractResourceContext(
     override val remainingWork: Double
         get() {
             val activeCommand = activeCommand ?: return 0.0
-            return computeRemainingWork(activeCommand, clock.millis())
+            val now = clock.millis()
+
+            return if (_remainingWorkFlush < now) {
+                _remainingWorkFlush = now
+                computeRemainingWork(activeCommand, now).also { _remainingWork = it }
+            } else {
+                _remainingWork
+            }
         }
+    private var _remainingWork: Double = 0.0
+    private var _remainingWorkFlush: Long = Long.MIN_VALUE
 
     /**
      * A flag to indicate the state of the context.
@@ -201,6 +210,9 @@ public abstract class SimAbstractResourceContext(
                     // Flush may not be called when the resource consumer has finished
                     throw IllegalStateException()
             }
+
+            // Flush remaining work cache
+            _remainingWorkFlush = Long.MIN_VALUE
         } catch (cause: Throwable) {
             doStop(cause)
         } finally {