simulator: Optimize bottlenecks in resource layer

This pull request addresses several bottlenecks that were present in the 
`opendc-simulator-resources` layer and  `TimerScheduler`.
These changes result into a 4x performance improvement for the energy experiments 
we are currently doing.

* The use of `StateFlow` has been removed where possible. Profiling shows that 
emitting changes to `StateFlow` becomes a bottleneck in a single-thread context.
* `SimSpeedConsumerAdapter` is an alternative for obtaining the changes in 
speed of a resource.

 **Breaking API Changes**
* `SimResourceSource` does not expose `speed` as `StateFlow` anymore. To monitor speed changes, use `SimSpeedConsumerAdapter`.
* Power draw in `SimBareMetalMachine` is not exposed as `StateFlow` anymore.

3 files changed, 19 insertions, 21 deletions

diff --git a/simulator/opendc-simulator/opendc-simulator-resources/src/test/kotlin/org/opendc/simulator/resources/SimResourceAggregatorMaxMinTest.kt b/simulator/opendc-simulator/opendc-simulator-resources/src/test/kotlin/org/opendc/simulator/resources/SimResourceAggregatorMaxMinTest.kt
index de864c1c..bf8c6d1f 100644
--- a/simulator/opendc-simulator/opendc-simulator-resources/src/test/kotlin/org/opendc/simulator/resources/SimResourceAggregatorMaxMinTest.kt
+++ b/simulator/opendc-simulator/opendc-simulator-resources/src/test/kotlin/org/opendc/simulator/resources/SimResourceAggregatorMaxMinTest.kt
@@ -26,12 +26,12 @@ import io.mockk.every
 import io.mockk.mockk
 import io.mockk.verify
 import kotlinx.coroutines.*
-import kotlinx.coroutines.flow.toList
 import kotlinx.coroutines.test.runBlockingTest
 import org.junit.jupiter.api.Assertions.assertEquals
 import org.junit.jupiter.api.Test
 import org.junit.jupiter.api.assertAll
 import org.junit.jupiter.api.assertThrows
+import org.opendc.simulator.resources.consumer.SimSpeedConsumerAdapter
 import org.opendc.simulator.resources.consumer.SimWorkConsumer
 import org.opendc.simulator.utils.DelayControllerClockAdapter
 import org.opendc.utils.TimerScheduler
@@ -47,15 +47,18 @@ internal class SimResourceAggregatorMaxMinTest {
         val scheduler = TimerScheduler<Any>(coroutineContext, clock)
 
         val aggregator = SimResourceAggregatorMaxMin(clock)
+        val forwarder = SimResourceForwarder()
         val sources = listOf(
-            SimResourceSource(1.0, clock, scheduler),
+            forwarder,
             SimResourceSource(1.0, clock, scheduler)
         )
         sources.forEach(aggregator::addInput)
 
         val consumer = SimWorkConsumer(1.0, 0.5)
         val usage = mutableListOf<Double>()
-        val job = launch { sources[0].speed.toList(usage) }
+        val source = SimResourceSource(1.0, clock, scheduler)
+        val adapter = SimSpeedConsumerAdapter(forwarder, usage::add)
+        source.startConsumer(adapter)
 
         try {
             aggregator.output.consume(consumer)
@@ -67,7 +70,6 @@ internal class SimResourceAggregatorMaxMinTest {
             )
         } finally {
             aggregator.output.close()
-            job.cancel()
         }
     }
 
@@ -85,18 +87,17 @@ internal class SimResourceAggregatorMaxMinTest {
 
         val consumer = SimWorkConsumer(2.0, 1.0)
         val usage = mutableListOf<Double>()
-        val job = launch { sources[0].speed.toList(usage) }
+        val adapter = SimSpeedConsumerAdapter(consumer, usage::add)
 
         try {
-            aggregator.output.consume(consumer)
+            aggregator.output.consume(adapter)
             yield()
             assertAll(
                 { assertEquals(1000, currentTime) },
-                { assertEquals(listOf(0.0, 1.0, 0.0), usage) }
+                { assertEquals(listOf(0.0, 2.0, 0.0), usage) }
             )
         } finally {
             aggregator.output.close()
-            job.cancel()
         }
     }
 
diff --git a/simulator/opendc-simulator/opendc-simulator-resources/src/test/kotlin/org/opendc/simulator/resources/SimResourceSourceTest.kt b/simulator/opendc-simulator/opendc-simulator-resources/src/test/kotlin/org/opendc/simulator/resources/SimResourceSourceTest.kt
index 58e19421..dbba6160 100644
--- a/simulator/opendc-simulator/opendc-simulator-resources/src/test/kotlin/org/opendc/simulator/resources/SimResourceSourceTest.kt
+++ b/simulator/opendc-simulator/opendc-simulator-resources/src/test/kotlin/org/opendc/simulator/resources/SimResourceSourceTest.kt
@@ -27,10 +27,10 @@ import io.mockk.mockk
 import io.mockk.spyk
 import io.mockk.verify
 import kotlinx.coroutines.*
-import kotlinx.coroutines.flow.toList
 import kotlinx.coroutines.test.runBlockingTest
 import org.junit.jupiter.api.*
 import org.junit.jupiter.api.Assertions.assertEquals
+import org.opendc.simulator.resources.consumer.SimSpeedConsumerAdapter
 import org.opendc.simulator.resources.consumer.SimWorkConsumer
 import org.opendc.simulator.utils.DelayControllerClockAdapter
 import org.opendc.utils.TimerScheduler
@@ -54,11 +54,10 @@ class SimResourceSourceTest {
 
         try {
             val res = mutableListOf<Double>()
-            val job = launch { provider.speed.toList(res) }
+            val adapter = SimSpeedConsumerAdapter(consumer, res::add)
 
-            provider.consume(consumer)
+            provider.consume(adapter)
 
-            job.cancel()
             assertEquals(listOf(0.0, capacity, 0.0), res) { "Speed is reported correctly" }
         } finally {
             scheduler.close()
@@ -102,11 +101,10 @@ class SimResourceSourceTest {
 
         try {
             val res = mutableListOf<Double>()
-            val job = launch { provider.speed.toList(res) }
+            val adapter = SimSpeedConsumerAdapter(consumer, res::add)
 
-            provider.consume(consumer)
+            provider.consume(adapter)
 
-            job.cancel()
             assertEquals(listOf(0.0, capacity, 0.0), res) { "Speed is reported correctly" }
         } finally {
             scheduler.close()
diff --git a/simulator/opendc-simulator/opendc-simulator-resources/src/test/kotlin/org/opendc/simulator/resources/SimResourceSwitchExclusiveTest.kt b/simulator/opendc-simulator/opendc-simulator-resources/src/test/kotlin/org/opendc/simulator/resources/SimResourceSwitchExclusiveTest.kt
index edd60502..9a40edc4 100644
--- a/simulator/opendc-simulator/opendc-simulator-resources/src/test/kotlin/org/opendc/simulator/resources/SimResourceSwitchExclusiveTest.kt
+++ b/simulator/opendc-simulator/opendc-simulator-resources/src/test/kotlin/org/opendc/simulator/resources/SimResourceSwitchExclusiveTest.kt
@@ -25,14 +25,13 @@ package org.opendc.simulator.resources
 import io.mockk.every
 import io.mockk.mockk
 import kotlinx.coroutines.ExperimentalCoroutinesApi
-import kotlinx.coroutines.flow.toList
-import kotlinx.coroutines.launch
 import kotlinx.coroutines.test.runBlockingTest
 import kotlinx.coroutines.yield
 import org.junit.jupiter.api.Assertions.assertEquals
 import org.junit.jupiter.api.Test
 import org.junit.jupiter.api.assertAll
 import org.junit.jupiter.api.assertThrows
+import org.opendc.simulator.resources.consumer.SimSpeedConsumerAdapter
 import org.opendc.simulator.resources.consumer.SimTraceConsumer
 import org.opendc.simulator.utils.DelayControllerClockAdapter
 import org.opendc.utils.TimerScheduler
@@ -65,17 +64,17 @@ internal class SimResourceSwitchExclusiveTest {
 
         val switch = SimResourceSwitchExclusive()
         val source = SimResourceSource(3200.0, clock, scheduler)
-
-        switch.addInput(source)
+        val forwarder = SimResourceForwarder()
+        val adapter = SimSpeedConsumerAdapter(forwarder, speed::add)
+        source.startConsumer(adapter)
+        switch.addInput(forwarder)
 
         val provider = switch.addOutput(3200.0)
-        val job = launch { source.speed.toList(speed) }
 
         try {
             provider.consume(workload)
             yield()
         } finally {
-            job.cancel()
             provider.close()
         }