merge: Migrate to flow-based simulation for low-level models

This pull request converts the `opendc-simulator-resources` module into a flow
simulator and adapts the existing low-level models (e.g., CPU, network, disk)
to this new flow simulator.

The flow simulator works differently from the uniform resource consumption
model, in that it models flow through a system of connections, as opposed to
resource consumptions. Concretely, this means that while in the uniform
resource consumption model, consumptions with the same usage are propagated to
the resources, in the flow simulator, only changes to the flow in the system
are propagated. 

Overall, this leads to less updates in the system and therefore higher
performance. The benchmarks shows that the new implementation obtains more than
double the performance of the old implementation. We have focused in the new
implementation on reducing the amount of work and memory
allocations/loads/stores per updates.

* Migrate from kotlinx-benchmark to jmh-gradle (for better profiling support)
* Use longer traces for benchmarks (to prevent measuring the benchmark
overhead)
* Use direct field access for perf-sensitive code
* Combine work and deadline to duration
* Add support for pushing flow from context (to eliminate the allocation for
every `SimResourceCommand`)
* Reduce memory allocations in SimResourceInterpreter, by revamping the way
timers are allocated.
* Simplify max-min aggregator implementation (by utilizing the new push
mechanism) 
* Invoke consumer callback on every invalidation (in order to propagate changes
downstream)
* Lazily push changes to resource context (by not updating the flow rate
immediately after a push, but only after an update)
* Remove onUpdate callback 
* Merge distributor and aggregator into switch 
* Separate push and pull flags 
* Remove failure callback from FlowSource 
* Create separate callbacks for remaining events 
* Make convergence callback optional
* Reduce field accesses in FlowConsumerContextImpl
* Optimize hot path in SimTraceWorkload
* Expose CPU time counters directly on hypervisor 
* Optimize telemetry collection

**Breaking API Changes**

* The entire `opendc-simulator-resources` module has been replaced by the
`opendc-simulator-flow` module.
* `SimHypervisor.Listener` has been removed in favour of a new interface that
exposes the performance counters of the hypervisor directly. To listen for
convergence, use `FlowConvergenceListener`.

8 files changed, 121 insertions, 143 deletions

diff --git a/opendc-simulator/opendc-simulator-power/build.gradle.kts b/opendc-simulator/opendc-simulator-power/build.gradle.kts
index f2a49964..5d8c8949 100644
--- a/opendc-simulator/opendc-simulator-power/build.gradle.kts
+++ b/opendc-simulator/opendc-simulator-power/build.gradle.kts
@@ -30,6 +30,8 @@ plugins {
 
 dependencies {
     api(platform(projects.opendcPlatform))
-    api(projects.opendcSimulator.opendcSimulatorResources)
+    api(projects.opendcSimulator.opendcSimulatorFlow)
     implementation(projects.opendcSimulator.opendcSimulatorCore)
+
+    testImplementation(libs.slf4j.simple)
 }
diff --git a/opendc-simulator/opendc-simulator-power/src/main/kotlin/org/opendc/simulator/power/SimPdu.kt b/opendc-simulator/opendc-simulator-power/src/main/kotlin/org/opendc/simulator/power/SimPdu.kt
index 3ce85d02..9f88fecc 100644
--- a/opendc-simulator/opendc-simulator-power/src/main/kotlin/org/opendc/simulator/power/SimPdu.kt
+++ b/opendc-simulator/opendc-simulator-power/src/main/kotlin/org/opendc/simulator/power/SimPdu.kt
@@ -22,52 +22,40 @@
 
 package org.opendc.simulator.power
 
-import org.opendc.simulator.resources.*
+import org.opendc.simulator.flow.*
+import org.opendc.simulator.flow.mux.FlowMultiplexer
+import org.opendc.simulator.flow.mux.MaxMinFlowMultiplexer
 
 /**
  * A model of a Power Distribution Unit (PDU).
  *
- * @param interpreter The underlying [SimResourceInterpreter] to drive the simulation under the hood.
+ * @param engine The underlying [FlowEngine] to drive the simulation under the hood.
  * @param idlePower The idle power consumption of the PDU independent of the load on the PDU.
  * @param lossCoefficient The coefficient for the power loss of the PDU proportional to the square load.
  */
 public class SimPdu(
-    interpreter: SimResourceInterpreter,
+    engine: FlowEngine,
     private val idlePower: Double = 0.0,
     private val lossCoefficient: Double = 0.0,
 ) : SimPowerInlet() {
     /**
-     * The [SimResourceDistributor] that distributes the electricity over the PDU outlets.
+     * The [FlowMultiplexer] that distributes the electricity over the PDU outlets.
      */
-    private val distributor = SimResourceDistributorMaxMin(interpreter)
+    private val mux = MaxMinFlowMultiplexer(engine)
 
     /**
-     * Create a new PDU outlet.
+     * The [FlowForwarder] that represents the input of the PDU.
      */
-    public fun newOutlet(): Outlet = Outlet(distributor.newOutput())
-
-    override fun createConsumer(): SimResourceConsumer = object : SimResourceConsumer by distributor {
-        override fun onNext(ctx: SimResourceContext): SimResourceCommand {
-            return when (val cmd = distributor.onNext(ctx)) {
-                is SimResourceCommand.Consume -> {
-                    val duration = cmd.work / cmd.limit
-                    val loss = computePowerLoss(cmd.limit)
-                    val newLimit = cmd.limit + loss
+    private val output = mux.newOutput()
 
-                    SimResourceCommand.Consume(duration * newLimit, newLimit, cmd.deadline)
-                }
-                is SimResourceCommand.Idle -> {
-                    val loss = computePowerLoss(0.0)
-                    if (loss > 0.0)
-                        SimResourceCommand.Consume(Double.POSITIVE_INFINITY, loss, cmd.deadline)
-                    else
-                        cmd
-                }
-                else -> cmd
-            }
-        }
+    /**
+     * Create a new PDU outlet.
+     */
+    public fun newOutlet(): Outlet = Outlet(mux, mux.newInput())
 
-        override fun toString(): String = "SimPdu.Consumer"
+    override fun createSource(): FlowSource = FlowMapper(output) { _, rate ->
+        val loss = computePowerLoss(rate)
+        rate + loss
     }
 
     override fun toString(): String = "SimPdu"
@@ -83,9 +71,9 @@ public class SimPdu(
     /**
      * A PDU outlet.
      */
-    public class Outlet(private val provider: SimResourceCloseableProvider) : SimPowerOutlet(), AutoCloseable {
+    public class Outlet(private val switch: FlowMultiplexer, private val provider: FlowConsumer) : SimPowerOutlet(), AutoCloseable {
         override fun onConnect(inlet: SimPowerInlet) {
-            provider.startConsumer(inlet.createConsumer())
+            provider.startConsumer(inlet.createSource())
         }
 
         override fun onDisconnect(inlet: SimPowerInlet) {
@@ -96,7 +84,7 @@ public class SimPdu(
          * Remove the outlet from the PDU.
          */
         override fun close() {
-            provider.close()
+            switch.removeInput(provider)
         }
 
         override fun toString(): String = "SimPdu.Outlet"
diff --git a/opendc-simulator/opendc-simulator-power/src/main/kotlin/org/opendc/simulator/power/SimPowerInlet.kt b/opendc-simulator/opendc-simulator-power/src/main/kotlin/org/opendc/simulator/power/SimPowerInlet.kt
index 0ac1f199..de587b7f 100644
--- a/opendc-simulator/opendc-simulator-power/src/main/kotlin/org/opendc/simulator/power/SimPowerInlet.kt
+++ b/opendc-simulator/opendc-simulator-power/src/main/kotlin/org/opendc/simulator/power/SimPowerInlet.kt
@@ -22,7 +22,7 @@
 
 package org.opendc.simulator.power
 
-import org.opendc.simulator.resources.SimResourceConsumer
+import org.opendc.simulator.flow.FlowSource
 
 /**
  * An abstract inlet that consumes electricity from a power outlet.
@@ -42,7 +42,7 @@ public abstract class SimPowerInlet {
     internal var _outlet: SimPowerOutlet? = null
 
     /**
-     * Create a [SimResourceConsumer] which represents the consumption of electricity from the power outlet.
+     * Create a [FlowSource] which represents the consumption of electricity from the power outlet.
      */
-    public abstract fun createConsumer(): SimResourceConsumer
+    public abstract fun createSource(): FlowSource
 }
diff --git a/opendc-simulator/opendc-simulator-power/src/main/kotlin/org/opendc/simulator/power/SimPowerSource.kt b/opendc-simulator/opendc-simulator-power/src/main/kotlin/org/opendc/simulator/power/SimPowerSource.kt
index 3ef8ccc6..07e9f52e 100644
--- a/opendc-simulator/opendc-simulator-power/src/main/kotlin/org/opendc/simulator/power/SimPowerSource.kt
+++ b/opendc-simulator/opendc-simulator-power/src/main/kotlin/org/opendc/simulator/power/SimPowerSource.kt
@@ -22,28 +22,28 @@
 
 package org.opendc.simulator.power
 
-import org.opendc.simulator.resources.SimResourceInterpreter
-import org.opendc.simulator.resources.SimResourceSource
+import org.opendc.simulator.flow.FlowEngine
+import org.opendc.simulator.flow.FlowSink
 
 /**
  * A [SimPowerOutlet] that represents a source of electricity.
  *
- * @param interpreter The underlying [SimResourceInterpreter] to drive the simulation under the hood.
+ * @param engine The underlying [FlowEngine] to drive the simulation under the hood.
  */
-public class SimPowerSource(interpreter: SimResourceInterpreter, public val capacity: Double) : SimPowerOutlet() {
+public class SimPowerSource(engine: FlowEngine, public val capacity: Double) : SimPowerOutlet() {
     /**
      * The resource source that drives this power source.
      */
-    private val source = SimResourceSource(capacity, interpreter)
+    private val source = FlowSink(engine, capacity)
 
     /**
      * The power draw at this instant.
      */
     public val powerDraw: Double
-        get() = source.speed
+        get() = source.rate
 
     override fun onConnect(inlet: SimPowerInlet) {
-        source.startConsumer(inlet.createConsumer())
+        source.startConsumer(inlet.createSource())
     }
 
     override fun onDisconnect(inlet: SimPowerInlet) {
diff --git a/opendc-simulator/opendc-simulator-power/src/main/kotlin/org/opendc/simulator/power/SimUps.kt b/opendc-simulator/opendc-simulator-power/src/main/kotlin/org/opendc/simulator/power/SimUps.kt
index f9431d21..46d659f8 100644
--- a/opendc-simulator/opendc-simulator-power/src/main/kotlin/org/opendc/simulator/power/SimUps.kt
+++ b/opendc-simulator/opendc-simulator-power/src/main/kotlin/org/opendc/simulator/power/SimUps.kt
@@ -22,63 +22,54 @@
 
 package org.opendc.simulator.power
 
-import org.opendc.simulator.resources.*
+import org.opendc.simulator.flow.*
+import org.opendc.simulator.flow.mux.MaxMinFlowMultiplexer
 
 /**
  * A model of an Uninterruptible Power Supply (UPS).
  *
  * This model aggregates multiple power sources into a single source in order to ensure that power is always available.
  *
- * @param interpreter The underlying [SimResourceInterpreter] to drive the simulation under the hood.
+ * @param engine The underlying [FlowEngine] to drive the simulation under the hood.
  * @param idlePower The idle power consumption of the UPS independent of the load.
  * @param lossCoefficient The coefficient for the power loss of the UPS proportional to the load.
  */
 public class SimUps(
-    interpreter: SimResourceInterpreter,
+    private val engine: FlowEngine,
     private val idlePower: Double = 0.0,
     private val lossCoefficient: Double = 0.0,
 ) : SimPowerOutlet() {
     /**
      * The resource aggregator used to combine the input sources.
      */
-    private val aggregator = SimResourceAggregatorMaxMin(interpreter)
+    private val mux = MaxMinFlowMultiplexer(engine)
+
+    /**
+     * The [FlowConsumer] that represents the output of the UPS.
+     */
+    private val provider = mux.newInput()
 
     /**
      * Create a new UPS outlet.
      */
     public fun newInlet(): SimPowerInlet {
-        val forward = SimResourceForwarder(isCoupled = true)
-        aggregator.addInput(forward)
+        val forward = FlowForwarder(engine, isCoupled = true)
+        forward.startConsumer(mux.newOutput())
         return Inlet(forward)
     }
 
     override fun onConnect(inlet: SimPowerInlet) {
-        val consumer = inlet.createConsumer()
-        aggregator.startConsumer(object : SimResourceConsumer by consumer {
-            override fun onNext(ctx: SimResourceContext): SimResourceCommand {
-                return when (val cmd = consumer.onNext(ctx)) {
-                    is SimResourceCommand.Consume -> {
-                        val duration = cmd.work / cmd.limit
-                        val loss = computePowerLoss(cmd.limit)
-                        val newLimit = cmd.limit + loss
+        val source = inlet.createSource()
+        val mapper = FlowMapper(source) { _, rate ->
+            val loss = computePowerLoss(rate)
+            rate + loss
+        }
 
-                        SimResourceCommand.Consume(duration * newLimit, newLimit, cmd.deadline)
-                    }
-                    is SimResourceCommand.Idle -> {
-                        val loss = computePowerLoss(0.0)
-                        if (loss > 0.0)
-                            SimResourceCommand.Consume(Double.POSITIVE_INFINITY, loss, cmd.deadline)
-                        else
-                            cmd
-                    }
-                    else -> cmd
-                }
-            }
-        })
+        provider.startConsumer(mapper)
     }
 
     override fun onDisconnect(inlet: SimPowerInlet) {
-        aggregator.cancel()
+        provider.cancel()
     }
 
     /**
@@ -92,8 +83,8 @@ public class SimUps(
     /**
      * A UPS inlet.
      */
-    public inner class Inlet(private val forwarder: SimResourceTransformer) : SimPowerInlet(), AutoCloseable {
-        override fun createConsumer(): SimResourceConsumer = forwarder
+    public inner class Inlet(private val forwarder: FlowForwarder) : SimPowerInlet(), AutoCloseable {
+        override fun createSource(): FlowSource = forwarder
 
         /**
          * Remove the inlet from the PSU.
diff --git a/opendc-simulator/opendc-simulator-power/src/test/kotlin/org/opendc/simulator/power/SimPduTest.kt b/opendc-simulator/opendc-simulator-power/src/test/kotlin/org/opendc/simulator/power/SimPduTest.kt
index 17a174b7..eb823eb1 100644
--- a/opendc-simulator/opendc-simulator-power/src/test/kotlin/org/opendc/simulator/power/SimPduTest.kt
+++ b/opendc-simulator/opendc-simulator-power/src/test/kotlin/org/opendc/simulator/power/SimPduTest.kt
@@ -28,10 +28,9 @@ import org.junit.jupiter.api.Assertions.assertEquals
 import org.junit.jupiter.api.Test
 import org.junit.jupiter.api.assertThrows
 import org.opendc.simulator.core.runBlockingSimulation
-import org.opendc.simulator.resources.SimResourceConsumer
-import org.opendc.simulator.resources.SimResourceEvent
-import org.opendc.simulator.resources.SimResourceInterpreter
-import org.opendc.simulator.resources.consumer.SimWorkConsumer
+import org.opendc.simulator.flow.FlowEngine
+import org.opendc.simulator.flow.FlowSource
+import org.opendc.simulator.flow.source.FixedFlowSource
 
 /**
  * Test suite for the [SimPdu] class.
@@ -39,9 +38,9 @@ import org.opendc.simulator.resources.consumer.SimWorkConsumer
 internal class SimPduTest {
     @Test
     fun testZeroOutlets() = runBlockingSimulation {
-        val interpreter = SimResourceInterpreter(coroutineContext, clock)
-        val source = SimPowerSource(interpreter, capacity = 100.0)
-        val pdu = SimPdu(interpreter)
+        val engine = FlowEngine(coroutineContext, clock)
+        val source = SimPowerSource(engine, capacity = 100.0)
+        val pdu = SimPdu(engine)
         source.connect(pdu)
 
         assertEquals(0.0, source.powerDraw)
@@ -49,9 +48,9 @@ internal class SimPduTest {
 
     @Test
     fun testSingleOutlet() = runBlockingSimulation {
-        val interpreter = SimResourceInterpreter(coroutineContext, clock)
-        val source = SimPowerSource(interpreter, capacity = 100.0)
-        val pdu = SimPdu(interpreter)
+        val engine = FlowEngine(coroutineContext, clock)
+        val source = SimPowerSource(engine, capacity = 100.0)
+        val pdu = SimPdu(engine)
         source.connect(pdu)
         pdu.newOutlet().connect(SimpleInlet())
 
@@ -60,9 +59,9 @@ internal class SimPduTest {
 
     @Test
     fun testDoubleOutlet() = runBlockingSimulation {
-        val interpreter = SimResourceInterpreter(coroutineContext, clock)
-        val source = SimPowerSource(interpreter, capacity = 100.0)
-        val pdu = SimPdu(interpreter)
+        val engine = FlowEngine(coroutineContext, clock)
+        val source = SimPowerSource(engine, capacity = 100.0)
+        val pdu = SimPdu(engine)
         source.connect(pdu)
 
         pdu.newOutlet().connect(SimpleInlet())
@@ -73,28 +72,28 @@ internal class SimPduTest {
 
     @Test
     fun testDisconnect() = runBlockingSimulation {
-        val interpreter = SimResourceInterpreter(coroutineContext, clock)
-        val source = SimPowerSource(interpreter, capacity = 100.0)
-        val pdu = SimPdu(interpreter)
+        val engine = FlowEngine(coroutineContext, clock)
+        val source = SimPowerSource(engine, capacity = 100.0)
+        val pdu = SimPdu(engine)
         source.connect(pdu)
-        val consumer = spyk(SimWorkConsumer(100.0, utilization = 1.0))
+        val consumer = spyk(FixedFlowSource(100.0, utilization = 1.0))
         val inlet = object : SimPowerInlet() {
-            override fun createConsumer(): SimResourceConsumer = consumer
+            override fun createSource(): FlowSource = consumer
         }
 
         val outlet = pdu.newOutlet()
         outlet.connect(inlet)
         outlet.disconnect()
 
-        verify { consumer.onEvent(any(), SimResourceEvent.Exit) }
+        verify { consumer.onStop(any(), any(), any()) }
     }
 
     @Test
     fun testLoss() = runBlockingSimulation {
-        val interpreter = SimResourceInterpreter(coroutineContext, clock)
-        val source = SimPowerSource(interpreter, capacity = 100.0)
+        val engine = FlowEngine(coroutineContext, clock)
+        val source = SimPowerSource(engine, capacity = 100.0)
         // https://download.schneider-electric.com/files?p_Doc_Ref=SPD_NRAN-66CK3D_EN
-        val pdu = SimPdu(interpreter, idlePower = 1.5, lossCoefficient = 0.015)
+        val pdu = SimPdu(engine, idlePower = 1.5, lossCoefficient = 0.015)
         source.connect(pdu)
         pdu.newOutlet().connect(SimpleInlet())
         assertEquals(89.0, source.powerDraw, 0.01)
@@ -102,9 +101,9 @@ internal class SimPduTest {
 
     @Test
     fun testOutletClose() = runBlockingSimulation {
-        val interpreter = SimResourceInterpreter(coroutineContext, clock)
-        val source = SimPowerSource(interpreter, capacity = 100.0)
-        val pdu = SimPdu(interpreter)
+        val engine = FlowEngine(coroutineContext, clock)
+        val source = SimPowerSource(engine, capacity = 100.0)
+        val pdu = SimPdu(engine)
         source.connect(pdu)
         val outlet = pdu.newOutlet()
         outlet.close()
@@ -115,6 +114,6 @@ internal class SimPduTest {
     }
 
     class SimpleInlet : SimPowerInlet() {
-        override fun createConsumer(): SimResourceConsumer = SimWorkConsumer(100.0, utilization = 0.5)
+        override fun createSource(): FlowSource = FixedFlowSource(100.0, utilization = 0.5)
     }
 }
diff --git a/opendc-simulator/opendc-simulator-power/src/test/kotlin/org/opendc/simulator/power/SimPowerSourceTest.kt b/opendc-simulator/opendc-simulator-power/src/test/kotlin/org/opendc/simulator/power/SimPowerSourceTest.kt
index f3829ba1..76142103 100644
--- a/opendc-simulator/opendc-simulator-power/src/test/kotlin/org/opendc/simulator/power/SimPowerSourceTest.kt
+++ b/opendc-simulator/opendc-simulator-power/src/test/kotlin/org/opendc/simulator/power/SimPowerSourceTest.kt
@@ -31,10 +31,9 @@ import org.junit.jupiter.api.Test
 import org.junit.jupiter.api.assertDoesNotThrow
 import org.junit.jupiter.api.assertThrows
 import org.opendc.simulator.core.runBlockingSimulation
-import org.opendc.simulator.resources.SimResourceConsumer
-import org.opendc.simulator.resources.SimResourceEvent
-import org.opendc.simulator.resources.SimResourceInterpreter
-import org.opendc.simulator.resources.consumer.SimWorkConsumer
+import org.opendc.simulator.flow.FlowEngine
+import org.opendc.simulator.flow.FlowSource
+import org.opendc.simulator.flow.source.FixedFlowSource
 
 /**
  * Test suite for the [SimPowerSource]
@@ -42,8 +41,8 @@ import org.opendc.simulator.resources.consumer.SimWorkConsumer
 internal class SimPowerSourceTest {
     @Test
     fun testInitialState() = runBlockingSimulation {
-        val interpreter = SimResourceInterpreter(coroutineContext, clock)
-        val source = SimPowerSource(interpreter, capacity = 100.0)
+        val engine = FlowEngine(coroutineContext, clock)
+        val source = SimPowerSource(engine, capacity = 100.0)
 
         assertFalse(source.isConnected)
         assertNull(source.inlet)
@@ -52,8 +51,8 @@ internal class SimPowerSourceTest {
 
     @Test
     fun testDisconnectIdempotent() = runBlockingSimulation {
-        val interpreter = SimResourceInterpreter(coroutineContext, clock)
-        val source = SimPowerSource(interpreter, capacity = 100.0)
+        val engine = FlowEngine(coroutineContext, clock)
+        val source = SimPowerSource(engine, capacity = 100.0)
 
         assertDoesNotThrow { source.disconnect() }
         assertFalse(source.isConnected)
@@ -61,8 +60,8 @@ internal class SimPowerSourceTest {
 
     @Test
     fun testConnect() = runBlockingSimulation {
-        val interpreter = SimResourceInterpreter(coroutineContext, clock)
-        val source = SimPowerSource(interpreter, capacity = 100.0)
+        val engine = FlowEngine(coroutineContext, clock)
+        val source = SimPowerSource(engine, capacity = 100.0)
         val inlet = SimpleInlet()
 
         source.connect(inlet)
@@ -76,27 +75,27 @@ internal class SimPowerSourceTest {
 
     @Test
     fun testDisconnect() = runBlockingSimulation {
-        val interpreter = SimResourceInterpreter(coroutineContext, clock)
-        val source = SimPowerSource(interpreter, capacity = 100.0)
-        val consumer = spyk(SimWorkConsumer(100.0, utilization = 1.0))
+        val engine = FlowEngine(coroutineContext, clock)
+        val source = SimPowerSource(engine, capacity = 100.0)
+        val consumer = spyk(FixedFlowSource(100.0, utilization = 1.0))
         val inlet = object : SimPowerInlet() {
-            override fun createConsumer(): SimResourceConsumer = consumer
+            override fun createSource(): FlowSource = consumer
         }
 
         source.connect(inlet)
         source.disconnect()
 
-        verify { consumer.onEvent(any(), SimResourceEvent.Exit) }
+        verify { consumer.onStop(any(), any(), any()) }
     }
 
     @Test
     fun testDisconnectAssertion() = runBlockingSimulation {
-        val interpreter = SimResourceInterpreter(coroutineContext, clock)
-        val source = SimPowerSource(interpreter, capacity = 100.0)
+        val engine = FlowEngine(coroutineContext, clock)
+        val source = SimPowerSource(engine, capacity = 100.0)
         val inlet = mockk<SimPowerInlet>(relaxUnitFun = true)
         every { inlet.isConnected } returns false
         every { inlet._outlet } returns null
-        every { inlet.createConsumer() } returns SimWorkConsumer(100.0, utilization = 1.0)
+        every { inlet.createSource() } returns FixedFlowSource(100.0, utilization = 1.0)
 
         source.connect(inlet)
 
@@ -107,8 +106,8 @@ internal class SimPowerSourceTest {
 
     @Test
     fun testOutletAlreadyConnected() = runBlockingSimulation {
-        val interpreter = SimResourceInterpreter(coroutineContext, clock)
-        val source = SimPowerSource(interpreter, capacity = 100.0)
+        val engine = FlowEngine(coroutineContext, clock)
+        val source = SimPowerSource(engine, capacity = 100.0)
         val inlet = SimpleInlet()
 
         source.connect(inlet)
@@ -121,8 +120,8 @@ internal class SimPowerSourceTest {
 
     @Test
     fun testInletAlreadyConnected() = runBlockingSimulation {
-        val interpreter = SimResourceInterpreter(coroutineContext, clock)
-        val source = SimPowerSource(interpreter, capacity = 100.0)
+        val engine = FlowEngine(coroutineContext, clock)
+        val source = SimPowerSource(engine, capacity = 100.0)
         val inlet = mockk<SimPowerInlet>(relaxUnitFun = true)
         every { inlet.isConnected } returns true
 
@@ -132,6 +131,6 @@ internal class SimPowerSourceTest {
     }
 
     class SimpleInlet : SimPowerInlet() {
-        override fun createConsumer(): SimResourceConsumer = SimWorkConsumer(100.0, utilization = 1.0)
+        override fun createSource(): FlowSource = FixedFlowSource(100.0, utilization = 1.0)
     }
 }
diff --git a/opendc-simulator/opendc-simulator-power/src/test/kotlin/org/opendc/simulator/power/SimUpsTest.kt b/opendc-simulator/opendc-simulator-power/src/test/kotlin/org/opendc/simulator/power/SimUpsTest.kt
index 8d5fa857..a764a368 100644
--- a/opendc-simulator/opendc-simulator-power/src/test/kotlin/org/opendc/simulator/power/SimUpsTest.kt
+++ b/opendc-simulator/opendc-simulator-power/src/test/kotlin/org/opendc/simulator/power/SimUpsTest.kt
@@ -28,10 +28,9 @@ import org.junit.jupiter.api.Assertions.assertAll
 import org.junit.jupiter.api.Assertions.assertEquals
 import org.junit.jupiter.api.Test
 import org.opendc.simulator.core.runBlockingSimulation
-import org.opendc.simulator.resources.SimResourceConsumer
-import org.opendc.simulator.resources.SimResourceEvent
-import org.opendc.simulator.resources.SimResourceInterpreter
-import org.opendc.simulator.resources.consumer.SimWorkConsumer
+import org.opendc.simulator.flow.FlowEngine
+import org.opendc.simulator.flow.FlowSource
+import org.opendc.simulator.flow.source.FixedFlowSource
 
 /**
  * Test suite for the [SimUps] class.
@@ -39,9 +38,9 @@ import org.opendc.simulator.resources.consumer.SimWorkConsumer
 internal class SimUpsTest {
     @Test
     fun testSingleInlet() = runBlockingSimulation {
-        val interpreter = SimResourceInterpreter(coroutineContext, clock)
-        val source = SimPowerSource(interpreter, capacity = 100.0)
-        val ups = SimUps(interpreter)
+        val engine = FlowEngine(coroutineContext, clock)
+        val source = SimPowerSource(engine, capacity = 100.0)
+        val ups = SimUps(engine)
         source.connect(ups.newInlet())
         ups.connect(SimpleInlet())
 
@@ -50,10 +49,10 @@ internal class SimUpsTest {
 
     @Test
     fun testDoubleInlet() = runBlockingSimulation {
-        val interpreter = SimResourceInterpreter(coroutineContext, clock)
-        val source1 = SimPowerSource(interpreter, capacity = 100.0)
-        val source2 = SimPowerSource(interpreter, capacity = 100.0)
-        val ups = SimUps(interpreter)
+        val engine = FlowEngine(coroutineContext, clock)
+        val source1 = SimPowerSource(engine, capacity = 100.0)
+        val source2 = SimPowerSource(engine, capacity = 100.0)
+        val ups = SimUps(engine)
         source1.connect(ups.newInlet())
         source2.connect(ups.newInlet())
 
@@ -67,10 +66,10 @@ internal class SimUpsTest {
 
     @Test
     fun testLoss() = runBlockingSimulation {
-        val interpreter = SimResourceInterpreter(coroutineContext, clock)
-        val source = SimPowerSource(interpreter, capacity = 100.0)
+        val engine = FlowEngine(coroutineContext, clock)
+        val source = SimPowerSource(engine, capacity = 100.0)
         // https://download.schneider-electric.com/files?p_Doc_Ref=SPD_NRAN-66CK3D_EN
-        val ups = SimUps(interpreter, idlePower = 4.0, lossCoefficient = 0.05)
+        val ups = SimUps(engine, idlePower = 4.0, lossCoefficient = 0.05)
         source.connect(ups.newInlet())
         ups.connect(SimpleInlet())
 
@@ -79,24 +78,24 @@ internal class SimUpsTest {
 
     @Test
     fun testDisconnect() = runBlockingSimulation {
-        val interpreter = SimResourceInterpreter(coroutineContext, clock)
-        val source1 = SimPowerSource(interpreter, capacity = 100.0)
-        val source2 = SimPowerSource(interpreter, capacity = 100.0)
-        val ups = SimUps(interpreter)
+        val engine = FlowEngine(coroutineContext, clock)
+        val source1 = SimPowerSource(engine, capacity = 100.0)
+        val source2 = SimPowerSource(engine, capacity = 100.0)
+        val ups = SimUps(engine)
         source1.connect(ups.newInlet())
         source2.connect(ups.newInlet())
-        val consumer = spyk(SimWorkConsumer(100.0, utilization = 1.0))
+        val consumer = spyk(FixedFlowSource(100.0, utilization = 1.0))
         val inlet = object : SimPowerInlet() {
-            override fun createConsumer(): SimResourceConsumer = consumer
+            override fun createSource(): FlowSource = consumer
         }
 
         ups.connect(inlet)
         ups.disconnect()
 
-        verify { consumer.onEvent(any(), SimResourceEvent.Exit) }
+        verify { consumer.onStop(any(), any(), any()) }
     }
 
     class SimpleInlet : SimPowerInlet() {
-        override fun createConsumer(): SimResourceConsumer = SimWorkConsumer(100.0, utilization = 0.5)
+        override fun createSource(): FlowSource = FixedFlowSource(100.0, utilization = 0.5)
     }
 }