refactor(simulator): Migrate to flow-based simulation

This change renames the `opendc-simulator-resources` module into the
`opendc-simulator-flow` module to indicate that the core simulation
model of OpenDC is based around modelling and simulating flows.

Previously, the distinction between resource consumer and provider, and
input and output caused some confusion. By switching to a flow-based
model, this distinction is now clear (as in, the water flows from source
to consumer/sink).

6 files changed, 975 insertions, 0 deletions

diff --git a/opendc-simulator/opendc-simulator-flow/src/test/kotlin/org/opendc/simulator/flow/FlowConsumerContextTest.kt b/opendc-simulator/opendc-simulator-flow/src/test/kotlin/org/opendc/simulator/flow/FlowConsumerContextTest.kt
new file mode 100644
index 00000000..061ebea6
--- /dev/null
+++ b/opendc-simulator/opendc-simulator-flow/src/test/kotlin/org/opendc/simulator/flow/FlowConsumerContextTest.kt
@@ -0,0 +1,152 @@
+/*
+ * 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.simulator.flow
+
+import io.mockk.*
+import kotlinx.coroutines.*
+import org.junit.jupiter.api.*
+import org.opendc.simulator.core.runBlockingSimulation
+import org.opendc.simulator.flow.internal.FlowConsumerContextImpl
+import org.opendc.simulator.flow.internal.FlowEngineImpl
+import org.opendc.simulator.flow.source.FixedFlowSource
+
+/**
+ * A test suite for the [FlowConsumerContextImpl] class.
+ */
+class FlowConsumerContextTest {
+    @Test
+    fun testFlushWithoutCommand() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val consumer = object : FlowSource {
+            override fun onPull(conn: FlowConnection, now: Long, delta: Long): Long {
+                return if (now == 0L) {
+                    conn.push(1.0)
+                    1000
+                } else {
+                    conn.close()
+                    Long.MAX_VALUE
+                }
+            }
+        }
+
+        val logic = object : FlowConsumerLogic {}
+        val context = FlowConsumerContextImpl(engine, consumer, logic)
+
+        engine.scheduleSync(engine.clock.millis(), context)
+    }
+
+    @Test
+    fun testIntermediateFlush() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val consumer = FixedFlowSource(1.0, 1.0)
+
+        val logic = spyk(object : FlowConsumerLogic {})
+        val context = FlowConsumerContextImpl(engine, consumer, logic)
+        context.capacity = 1.0
+
+        context.start()
+        delay(1) // Delay 1 ms to prevent hitting the fast path
+        engine.scheduleSync(engine.clock.millis(), context)
+
+        verify(exactly = 2) { logic.onPush(any(), any(), any(), any()) }
+    }
+
+    @Test
+    fun testDoubleStart() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val consumer = object : FlowSource {
+            override fun onPull(conn: FlowConnection, now: Long, delta: Long): Long {
+                return if (now == 0L) {
+                    conn.push(0.0)
+                    1000
+                } else {
+                    conn.close()
+                    Long.MAX_VALUE
+                }
+            }
+        }
+
+        val logic = object : FlowConsumerLogic {}
+        val context = FlowConsumerContextImpl(engine, consumer, logic)
+
+        context.start()
+
+        assertThrows<IllegalStateException> {
+            context.start()
+        }
+    }
+
+    @Test
+    fun testIdempotentCapacityChange() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val consumer = spyk(object : FlowSource {
+            override fun onPull(conn: FlowConnection, now: Long, delta: Long): Long {
+                return if (now == 0L) {
+                    conn.push(1.0)
+                    1000
+                } else {
+                    conn.close()
+                    Long.MAX_VALUE
+                }
+            }
+        })
+
+        val logic = object : FlowConsumerLogic {}
+        val context = FlowConsumerContextImpl(engine, consumer, logic)
+        context.capacity = 4200.0
+        context.start()
+        context.capacity = 4200.0
+
+        verify(exactly = 0) { consumer.onEvent(any(), any(), FlowEvent.Capacity) }
+    }
+
+    @Test
+    fun testFailureNoInfiniteLoop() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+
+        val consumer = spyk(object : FlowSource {
+            override fun onPull(conn: FlowConnection, now: Long, delta: Long): Long {
+                conn.close()
+                return Long.MAX_VALUE
+            }
+
+            override fun onEvent(conn: FlowConnection, now: Long, event: FlowEvent) {
+                if (event == FlowEvent.Exit) throw IllegalStateException("onEvent")
+            }
+
+            override fun onFailure(conn: FlowConnection, cause: Throwable) {
+                throw IllegalStateException("onFailure")
+            }
+        })
+
+        val logic = object : FlowConsumerLogic {}
+
+        val context = FlowConsumerContextImpl(engine, consumer, logic)
+
+        context.start()
+
+        delay(1)
+
+        verify(exactly = 1) { consumer.onFailure(any(), any()) }
+    }
+}
diff --git a/opendc-simulator/opendc-simulator-flow/src/test/kotlin/org/opendc/simulator/flow/FlowForwarderTest.kt b/opendc-simulator/opendc-simulator-flow/src/test/kotlin/org/opendc/simulator/flow/FlowForwarderTest.kt
new file mode 100644
index 00000000..cbc48a4e
--- /dev/null
+++ b/opendc-simulator/opendc-simulator-flow/src/test/kotlin/org/opendc/simulator/flow/FlowForwarderTest.kt
@@ -0,0 +1,222 @@
+/*
+ * 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.simulator.flow
+
+import io.mockk.spyk
+import io.mockk.verify
+import kotlinx.coroutines.*
+import org.junit.jupiter.api.Assertions.*
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertThrows
+import org.opendc.simulator.core.runBlockingSimulation
+import org.opendc.simulator.flow.internal.FlowEngineImpl
+import org.opendc.simulator.flow.source.FixedFlowSource
+
+/**
+ * A test suite for the [FlowForwarder] class.
+ */
+internal class FlowForwarderTest {
+    @Test
+    fun testCancelImmediately() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val forwarder = FlowForwarder(engine)
+        val source = FlowSink(engine, 2000.0)
+
+        launch { source.consume(forwarder) }
+
+        forwarder.consume(object : FlowSource {
+            override fun onPull(conn: FlowConnection, now: Long, delta: Long): Long {
+                conn.close()
+                return Long.MAX_VALUE
+            }
+        })
+
+        forwarder.close()
+        source.cancel()
+    }
+
+    @Test
+    fun testCancel() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val forwarder = FlowForwarder(engine)
+        val source = FlowSink(engine, 2000.0)
+
+        launch { source.consume(forwarder) }
+
+        forwarder.consume(object : FlowSource {
+            var isFirst = true
+
+            override fun onPull(conn: FlowConnection, now: Long, delta: Long): Long {
+                return if (isFirst) {
+                    isFirst = false
+                    conn.push(1.0)
+                    10 * 1000
+                } else {
+                    conn.close()
+                    Long.MAX_VALUE
+                }
+            }
+        })
+
+        forwarder.close()
+        source.cancel()
+    }
+
+    @Test
+    fun testState() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val forwarder = FlowForwarder(engine)
+        val consumer = object : FlowSource {
+            override fun onPull(conn: FlowConnection, now: Long, delta: Long): Long {
+                conn.close()
+                return Long.MAX_VALUE
+            }
+        }
+
+        assertFalse(forwarder.isActive)
+
+        forwarder.startConsumer(consumer)
+        assertTrue(forwarder.isActive)
+
+        assertThrows<IllegalStateException> { forwarder.startConsumer(consumer) }
+
+        forwarder.cancel()
+        assertFalse(forwarder.isActive)
+
+        forwarder.close()
+        assertFalse(forwarder.isActive)
+    }
+
+    @Test
+    fun testCancelPendingDelegate() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val forwarder = FlowForwarder(engine)
+
+        val consumer = spyk(object : FlowSource {
+            override fun onPull(conn: FlowConnection, now: Long, delta: Long): Long {
+                conn.close()
+                return Long.MAX_VALUE
+            }
+        })
+
+        forwarder.startConsumer(consumer)
+        forwarder.cancel()
+
+        verify(exactly = 0) { consumer.onEvent(any(), any(), FlowEvent.Exit) }
+    }
+
+    @Test
+    fun testCancelStartedDelegate() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val forwarder = FlowForwarder(engine)
+        val source = FlowSink(engine, 2000.0)
+
+        val consumer = spyk(FixedFlowSource(2000.0, 1.0))
+
+        source.startConsumer(forwarder)
+        yield()
+        forwarder.startConsumer(consumer)
+        yield()
+        forwarder.cancel()
+
+        verify(exactly = 1) { consumer.onEvent(any(), any(), FlowEvent.Start) }
+        verify(exactly = 1) { consumer.onEvent(any(), any(), FlowEvent.Exit) }
+    }
+
+    @Test
+    fun testCancelPropagation() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val forwarder = FlowForwarder(engine)
+        val source = FlowSink(engine, 2000.0)
+
+        val consumer = spyk(FixedFlowSource(2000.0, 1.0))
+
+        source.startConsumer(forwarder)
+        yield()
+        forwarder.startConsumer(consumer)
+        yield()
+        source.cancel()
+
+        verify(exactly = 1) { consumer.onEvent(any(), any(), FlowEvent.Start) }
+        verify(exactly = 1) { consumer.onEvent(any(), any(), FlowEvent.Exit) }
+    }
+
+    @Test
+    fun testExitPropagation() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val forwarder = FlowForwarder(engine, isCoupled = true)
+        val source = FlowSink(engine, 2000.0)
+
+        val consumer = object : FlowSource {
+            override fun onPull(conn: FlowConnection, now: Long, delta: Long): Long {
+                conn.close()
+                return Long.MAX_VALUE
+            }
+        }
+
+        source.startConsumer(forwarder)
+        forwarder.consume(consumer)
+        yield()
+
+        assertFalse(forwarder.isActive)
+    }
+
+    @Test
+    fun testAdjustCapacity() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val forwarder = FlowForwarder(engine)
+        val source = FlowSink(engine, 1.0)
+
+        val consumer = spyk(FixedFlowSource(2.0, 1.0))
+        source.startConsumer(forwarder)
+
+        coroutineScope {
+            launch { forwarder.consume(consumer) }
+            delay(1000)
+            source.capacity = 0.5
+        }
+
+        assertEquals(3000, clock.millis())
+        verify(exactly = 1) { consumer.onEvent(any(), any(), FlowEvent.Capacity) }
+    }
+
+    @Test
+    fun testCounters() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val forwarder = FlowForwarder(engine)
+        val source = FlowSink(engine, 1.0)
+
+        val consumer = FixedFlowSource(2.0, 1.0)
+        source.startConsumer(forwarder)
+
+        forwarder.consume(consumer)
+
+        yield()
+
+        assertEquals(2.0, source.counters.actual)
+        assertEquals(source.counters.actual, forwarder.counters.actual) { "Actual work" }
+        assertEquals(source.counters.demand, forwarder.counters.demand) { "Work demand" }
+        assertEquals(source.counters.overcommit, forwarder.counters.overcommit) { "Overcommitted work" }
+        assertEquals(2000, clock.millis())
+    }
+}
diff --git a/opendc-simulator/opendc-simulator-flow/src/test/kotlin/org/opendc/simulator/flow/FlowSinkTest.kt b/opendc-simulator/opendc-simulator-flow/src/test/kotlin/org/opendc/simulator/flow/FlowSinkTest.kt
new file mode 100644
index 00000000..010a985e
--- /dev/null
+++ b/opendc-simulator/opendc-simulator-flow/src/test/kotlin/org/opendc/simulator/flow/FlowSinkTest.kt
@@ -0,0 +1,240 @@
+/*
+ * 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.simulator.flow
+
+import io.mockk.every
+import io.mockk.mockk
+import io.mockk.spyk
+import io.mockk.verify
+import kotlinx.coroutines.*
+import org.junit.jupiter.api.*
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.opendc.simulator.core.runBlockingSimulation
+import org.opendc.simulator.flow.internal.FlowEngineImpl
+import org.opendc.simulator.flow.source.FixedFlowSource
+import org.opendc.simulator.flow.source.FlowSourceRateAdapter
+
+/**
+ * A test suite for the [FlowSink] class.
+ */
+internal class FlowSinkTest {
+    @Test
+    fun testSpeed() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val capacity = 4200.0
+        val provider = FlowSink(engine, capacity)
+
+        val consumer = FixedFlowSource(4200.0, 1.0)
+
+        val res = mutableListOf<Double>()
+        val adapter = FlowSourceRateAdapter(consumer, res::add)
+
+        provider.consume(adapter)
+
+        assertEquals(listOf(0.0, capacity, 0.0), res) { "Speed is reported correctly" }
+    }
+
+    @Test
+    fun testAdjustCapacity() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val provider = FlowSink(engine, 1.0)
+
+        val consumer = spyk(FixedFlowSource(2.0, 1.0))
+
+        coroutineScope {
+            launch { provider.consume(consumer) }
+            delay(1000)
+            provider.capacity = 0.5
+        }
+        assertEquals(3000, clock.millis())
+        verify(exactly = 1) { consumer.onEvent(any(), any(), FlowEvent.Capacity) }
+    }
+
+    @Test
+    fun testSpeedLimit() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val capacity = 4200.0
+        val provider = FlowSink(engine, capacity)
+
+        val consumer = FixedFlowSource(capacity, 2.0)
+
+        val res = mutableListOf<Double>()
+        val adapter = FlowSourceRateAdapter(consumer, res::add)
+
+        provider.consume(adapter)
+
+        assertEquals(listOf(0.0, capacity, 0.0), res) { "Speed is reported correctly" }
+    }
+
+    /**
+     * Test to see whether no infinite recursion occurs when interrupting during [FlowSource.onStart] or
+     * [FlowSource.onPull].
+     */
+    @Test
+    fun testIntermediateInterrupt() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val capacity = 4200.0
+        val provider = FlowSink(engine, capacity)
+
+        val consumer = object : FlowSource {
+            override fun onPull(conn: FlowConnection, now: Long, delta: Long): Long {
+                conn.close()
+                return Long.MAX_VALUE
+            }
+
+            override fun onEvent(conn: FlowConnection, now: Long, event: FlowEvent) {
+                conn.pull()
+            }
+        }
+
+        provider.consume(consumer)
+    }
+
+    @Test
+    fun testInterrupt() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val capacity = 4200.0
+        val provider = FlowSink(engine, capacity)
+        lateinit var resCtx: FlowConnection
+
+        val consumer = object : FlowSource {
+            var isFirst = true
+
+            override fun onEvent(conn: FlowConnection, now: Long, event: FlowEvent) {
+                when (event) {
+                    FlowEvent.Start -> resCtx = conn
+                    else -> {}
+                }
+            }
+
+            override fun onPull(conn: FlowConnection, now: Long, delta: Long): Long {
+                return if (isFirst) {
+                    isFirst = false
+                    conn.push(1.0)
+                    4000
+                } else {
+                    conn.close()
+                    Long.MAX_VALUE
+                }
+            }
+        }
+
+        launch {
+            yield()
+            resCtx.pull()
+        }
+        provider.consume(consumer)
+
+        assertEquals(0, clock.millis())
+    }
+
+    @Test
+    fun testFailure() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val capacity = 4200.0
+        val provider = FlowSink(engine, capacity)
+
+        val consumer = mockk<FlowSource>(relaxUnitFun = true)
+        every { consumer.onEvent(any(), any(), eq(FlowEvent.Start)) }
+            .throws(IllegalStateException())
+
+        assertThrows<IllegalStateException> {
+            provider.consume(consumer)
+        }
+    }
+
+    @Test
+    fun testExceptionPropagationOnNext() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val capacity = 4200.0
+        val provider = FlowSink(engine, capacity)
+
+        val consumer = object : FlowSource {
+            var isFirst = true
+
+            override fun onPull(conn: FlowConnection, now: Long, delta: Long): Long {
+                return if (isFirst) {
+                    isFirst = false
+                    conn.push(1.0)
+                    1000
+                } else {
+                    throw IllegalStateException()
+                }
+            }
+        }
+
+        assertThrows<IllegalStateException> {
+            provider.consume(consumer)
+        }
+    }
+
+    @Test
+    fun testConcurrentConsumption() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val capacity = 4200.0
+        val provider = FlowSink(engine, capacity)
+
+        val consumer = FixedFlowSource(capacity, 1.0)
+
+        assertThrows<IllegalStateException> {
+            coroutineScope {
+                launch { provider.consume(consumer) }
+                provider.consume(consumer)
+            }
+        }
+    }
+
+    @Test
+    fun testCancelDuringConsumption() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+        val capacity = 4200.0
+        val provider = FlowSink(engine, capacity)
+
+        val consumer = FixedFlowSource(capacity, 1.0)
+
+        launch { provider.consume(consumer) }
+        delay(500)
+        provider.cancel()
+
+        yield()
+
+        assertEquals(500, clock.millis())
+    }
+
+    @Test
+    fun testInfiniteSleep() {
+        assertThrows<IllegalStateException> {
+            runBlockingSimulation {
+                val engine = FlowEngineImpl(coroutineContext, clock)
+                val capacity = 4200.0
+                val provider = FlowSink(engine, capacity)
+
+                val consumer = object : FlowSource {
+                    override fun onPull(conn: FlowConnection, now: Long, delta: Long): Long = Long.MAX_VALUE
+                }
+
+                provider.consume(consumer)
+            }
+        }
+    }
+}
diff --git a/opendc-simulator/opendc-simulator-flow/src/test/kotlin/org/opendc/simulator/flow/mux/SimResourceSwitchExclusiveTest.kt b/opendc-simulator/opendc-simulator-flow/src/test/kotlin/org/opendc/simulator/flow/mux/SimResourceSwitchExclusiveTest.kt
new file mode 100644
index 00000000..b503087e
--- /dev/null
+++ b/opendc-simulator/opendc-simulator-flow/src/test/kotlin/org/opendc/simulator/flow/mux/SimResourceSwitchExclusiveTest.kt
@@ -0,0 +1,157 @@
+/*
+ * 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.simulator.flow.mux
+
+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.core.runBlockingSimulation
+import org.opendc.simulator.flow.*
+import org.opendc.simulator.flow.internal.FlowEngineImpl
+import org.opendc.simulator.flow.source.FixedFlowSource
+import org.opendc.simulator.flow.source.FlowSourceRateAdapter
+import org.opendc.simulator.flow.source.TraceFlowSource
+
+/**
+ * Test suite for the [ForwardingFlowMultiplexer] class.
+ */
+internal class SimResourceSwitchExclusiveTest {
+    /**
+     * Test a trace workload.
+     */
+    @Test
+    fun testTrace() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+
+        val speed = mutableListOf<Double>()
+
+        val duration = 5 * 60L
+        val workload =
+            TraceFlowSource(
+                sequenceOf(
+                    TraceFlowSource.Fragment(duration * 1000, 28.0),
+                    TraceFlowSource.Fragment(duration * 1000, 3500.0),
+                    TraceFlowSource.Fragment(duration * 1000, 0.0),
+                    TraceFlowSource.Fragment(duration * 1000, 183.0)
+                ),
+            )
+
+        val switch = ForwardingFlowMultiplexer(engine)
+        val source = FlowSink(engine, 3200.0)
+        val forwarder = FlowForwarder(engine)
+        val adapter = FlowSourceRateAdapter(forwarder, speed::add)
+        source.startConsumer(adapter)
+        switch.addOutput(forwarder)
+
+        val provider = switch.newInput()
+        provider.consume(workload)
+        yield()
+
+        assertAll(
+            { assertEquals(listOf(0.0, 28.0, 3200.0, 0.0, 183.0, 0.0), speed) { "Correct speed" } },
+            { assertEquals(5 * 60L * 4000, clock.millis()) { "Took enough time" } }
+        )
+    }
+
+    /**
+     * Test runtime workload on hypervisor.
+     */
+    @Test
+    fun testRuntimeWorkload() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+
+        val duration = 5 * 60L * 1000
+        val workload = FixedFlowSource(duration * 3.2, 1.0)
+
+        val switch = ForwardingFlowMultiplexer(engine)
+        val source = FlowSink(engine, 3200.0)
+
+        switch.addOutput(source)
+
+        val provider = switch.newInput()
+        provider.consume(workload)
+        yield()
+
+        assertEquals(duration, clock.millis()) { "Took enough time" }
+    }
+
+    /**
+     * Test two workloads running sequentially.
+     */
+    @Test
+    fun testTwoWorkloads() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+
+        val duration = 5 * 60L * 1000
+        val workload = object : FlowSource {
+            var isFirst = true
+
+            override fun onEvent(conn: FlowConnection, now: Long, event: FlowEvent) {
+                when (event) {
+                    FlowEvent.Start -> isFirst = true
+                    else -> {}
+                }
+            }
+
+            override fun onPull(conn: FlowConnection, now: Long, delta: Long): Long {
+                return if (isFirst) {
+                    isFirst = false
+                    conn.push(1.0)
+                    duration
+                } else {
+                    conn.close()
+                    Long.MAX_VALUE
+                }
+            }
+        }
+
+        val switch = ForwardingFlowMultiplexer(engine)
+        val source = FlowSink(engine, 3200.0)
+
+        switch.addOutput(source)
+
+        val provider = switch.newInput()
+        provider.consume(workload)
+        yield()
+        provider.consume(workload)
+        assertEquals(duration * 2, clock.millis()) { "Took enough time" }
+    }
+
+    /**
+     * Test concurrent workloads on the machine.
+     */
+    @Test
+    fun testConcurrentWorkloadFails() = runBlockingSimulation {
+        val engine = FlowEngineImpl(coroutineContext, clock)
+
+        val switch = ForwardingFlowMultiplexer(engine)
+        val source = FlowSink(engine, 3200.0)
+
+        switch.addOutput(source)
+
+        switch.newInput()
+        assertThrows<IllegalStateException> { switch.newInput() }
+    }
+}
diff --git a/opendc-simulator/opendc-simulator-flow/src/test/kotlin/org/opendc/simulator/flow/mux/SimResourceSwitchMaxMinTest.kt b/opendc-simulator/opendc-simulator-flow/src/test/kotlin/org/opendc/simulator/flow/mux/SimResourceSwitchMaxMinTest.kt
new file mode 100644
index 00000000..089a8d78
--- /dev/null
+++ b/opendc-simulator/opendc-simulator-flow/src/test/kotlin/org/opendc/simulator/flow/mux/SimResourceSwitchMaxMinTest.kt
@@ -0,0 +1,147 @@
+/*
+ * 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.simulator.flow.mux
+
+import kotlinx.coroutines.coroutineScope
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.yield
+import org.junit.jupiter.api.*
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.opendc.simulator.core.runBlockingSimulation
+import org.opendc.simulator.flow.FlowSink
+import org.opendc.simulator.flow.consume
+import org.opendc.simulator.flow.internal.FlowEngineImpl
+import org.opendc.simulator.flow.source.FixedFlowSource
+import org.opendc.simulator.flow.source.TraceFlowSource
+
+/**
+ * Test suite for the [FlowMultiplexer] implementations
+ */
+internal class SimResourceSwitchMaxMinTest {
+    @Test
+    fun testSmoke() = runBlockingSimulation {
+        val scheduler = FlowEngineImpl(coroutineContext, clock)
+        val switch = MaxMinFlowMultiplexer(scheduler)
+
+        val sources = List(2) { FlowSink(scheduler, 2000.0) }
+        sources.forEach { switch.addOutput(it) }
+
+        val provider = switch.newInput()
+        val consumer = FixedFlowSource(2000.0, 1.0)
+
+        try {
+            provider.consume(consumer)
+            yield()
+        } finally {
+            switch.clear()
+        }
+    }
+
+    /**
+     * Test overcommitting of resources via the hypervisor with a single VM.
+     */
+    @Test
+    fun testOvercommittedSingle() = runBlockingSimulation {
+        val scheduler = FlowEngineImpl(coroutineContext, clock)
+
+        val duration = 5 * 60L
+        val workload =
+            TraceFlowSource(
+                sequenceOf(
+                    TraceFlowSource.Fragment(duration * 1000, 28.0),
+                    TraceFlowSource.Fragment(duration * 1000, 3500.0),
+                    TraceFlowSource.Fragment(duration * 1000, 0.0),
+                    TraceFlowSource.Fragment(duration * 1000, 183.0)
+                ),
+            )
+
+        val switch = MaxMinFlowMultiplexer(scheduler)
+        val provider = switch.newInput()
+
+        try {
+            switch.addOutput(FlowSink(scheduler, 3200.0))
+            provider.consume(workload)
+            yield()
+        } finally {
+            switch.clear()
+        }
+
+        assertAll(
+            { assertEquals(1113300.0, switch.counters.demand, "Requested work does not match") },
+            { assertEquals(1023300.0, switch.counters.actual, "Actual work does not match") },
+            { assertEquals(90000.0, switch.counters.overcommit, "Overcommitted work does not match") },
+            { assertEquals(1200000, clock.millis()) }
+        )
+    }
+
+    /**
+     * Test overcommitting of resources via the hypervisor with two VMs.
+     */
+    @Test
+    fun testOvercommittedDual() = runBlockingSimulation {
+        val scheduler = FlowEngineImpl(coroutineContext, clock)
+
+        val duration = 5 * 60L
+        val workloadA =
+            TraceFlowSource(
+                sequenceOf(
+                    TraceFlowSource.Fragment(duration * 1000, 28.0),
+                    TraceFlowSource.Fragment(duration * 1000, 3500.0),
+                    TraceFlowSource.Fragment(duration * 1000, 0.0),
+                    TraceFlowSource.Fragment(duration * 1000, 183.0)
+                ),
+            )
+        val workloadB =
+            TraceFlowSource(
+                sequenceOf(
+                    TraceFlowSource.Fragment(duration * 1000, 28.0),
+                    TraceFlowSource.Fragment(duration * 1000, 3100.0),
+                    TraceFlowSource.Fragment(duration * 1000, 0.0),
+                    TraceFlowSource.Fragment(duration * 1000, 73.0)
+                )
+            )
+
+        val switch = MaxMinFlowMultiplexer(scheduler)
+        val providerA = switch.newInput()
+        val providerB = switch.newInput()
+
+        try {
+            switch.addOutput(FlowSink(scheduler, 3200.0))
+
+            coroutineScope {
+                launch { providerA.consume(workloadA) }
+                providerB.consume(workloadB)
+            }
+
+            yield()
+        } finally {
+            switch.clear()
+        }
+        assertAll(
+            { assertEquals(2073600.0, switch.counters.demand, "Requested work does not match") },
+            { assertEquals(1053600.0, switch.counters.actual, "Granted work does not match") },
+            { assertEquals(1020000.0, switch.counters.overcommit, "Overcommitted work does not match") },
+            { assertEquals(1200000, clock.millis()) }
+        )
+    }
+}
diff --git a/opendc-simulator/opendc-simulator-flow/src/test/kotlin/org/opendc/simulator/flow/source/FixedFlowSourceTest.kt b/opendc-simulator/opendc-simulator-flow/src/test/kotlin/org/opendc/simulator/flow/source/FixedFlowSourceTest.kt
new file mode 100644
index 00000000..8396d346
--- /dev/null
+++ b/opendc-simulator/opendc-simulator-flow/src/test/kotlin/org/opendc/simulator/flow/source/FixedFlowSourceTest.kt
@@ -0,0 +1,57 @@
+/*
+ * 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.simulator.flow.source
+
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Test
+import org.opendc.simulator.core.runBlockingSimulation
+import org.opendc.simulator.flow.FlowSink
+import org.opendc.simulator.flow.consume
+import org.opendc.simulator.flow.internal.FlowEngineImpl
+
+/**
+ * A test suite for the [FixedFlowSource] class.
+ */
+internal class FixedFlowSourceTest {
+    @Test
+    fun testSmoke() = runBlockingSimulation {
+        val scheduler = FlowEngineImpl(coroutineContext, clock)
+        val provider = FlowSink(scheduler, 1.0)
+
+        val consumer = FixedFlowSource(1.0, 1.0)
+
+        provider.consume(consumer)
+        assertEquals(1000, clock.millis())
+    }
+
+    @Test
+    fun testUtilization() = runBlockingSimulation {
+        val scheduler = FlowEngineImpl(coroutineContext, clock)
+        val provider = FlowSink(scheduler, 1.0)
+
+        val consumer = FixedFlowSource(1.0, 0.5)
+
+        provider.consume(consumer)
+        assertEquals(2000, clock.millis())
+    }
+}