simulator: Remove concept of resource lifecycle

This change removes the AutoCloseable interface from the
SimResourceProvider and removes the concept of a resource lifecycle.
Instead, resource providers are now either active (running a resource
consumer) or in-active (being idle), which simplifies implementation.

10 files changed, 87 insertions, 77 deletions

diff --git a/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimAbstractResourceAggregator.kt b/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimAbstractResourceAggregator.kt
index 5fe7d7bb..84217278 100644
--- a/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimAbstractResourceAggregator.kt
+++ b/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimAbstractResourceAggregator.kt
@@ -56,8 +56,6 @@ public abstract class SimAbstractResourceAggregator(
 
     /* SimResourceAggregator */
     override fun addInput(input: SimResourceProvider) {
-        check(state != SimResourceState.Stopped) { "Aggregator has been stopped" }
-
         val consumer = Consumer()
         _inputs.add(input)
         _inputConsumers.add(consumer)
@@ -70,8 +68,8 @@ public abstract class SimAbstractResourceAggregator(
     private val _inputConsumers = mutableListOf<Consumer>()
 
     /* SimResourceProvider */
-    override val state: SimResourceState
-        get() = _output.state
+    override val isActive: Boolean
+        get() = _output.isActive
 
     override val capacity: Double
         get() = _output.capacity
@@ -97,10 +95,6 @@ public abstract class SimAbstractResourceAggregator(
         _output.interrupt()
     }
 
-    override fun close() {
-        _output.close()
-    }
-
     private val _output = object : SimAbstractResourceProvider(interpreter, parent, initialCapacity = 0.0) {
         override fun createLogic(): SimResourceProviderLogic {
             return object : SimResourceProviderLogic {
diff --git a/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimAbstractResourceProvider.kt b/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimAbstractResourceProvider.kt
index de26f99e..c1b1450e 100644
--- a/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimAbstractResourceProvider.kt
+++ b/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimAbstractResourceProvider.kt
@@ -33,6 +33,12 @@ public abstract class SimAbstractResourceProvider(
     initialCapacity: Double
 ) : SimResourceProvider {
     /**
+     * A flag to indicate that the resource provider is active.
+     */
+    public override val isActive: Boolean
+        get() = ctx != null
+
+    /**
      * The capacity of the resource.
      */
     public override var capacity: Double = initialCapacity
@@ -67,12 +73,6 @@ public abstract class SimAbstractResourceProvider(
         private set
 
     /**
-     * The state of the resource provider.
-     */
-    final override var state: SimResourceState = SimResourceState.Pending
-        private set
-
-    /**
      * Construct the [SimResourceProviderLogic] instance for a new consumer.
      */
     protected abstract fun createLogic(): SimResourceProviderLogic
@@ -96,21 +96,15 @@ public abstract class SimAbstractResourceProvider(
     }
 
     final override fun startConsumer(consumer: SimResourceConsumer) {
-        check(state == SimResourceState.Pending) { "Resource is in invalid state" }
+        check(ctx == null) { "Resource is in invalid state" }
         val ctx = interpreter.newContext(consumer, createLogic(), parent)
 
         ctx.capacity = capacity
         this.ctx = ctx
-        this.state = SimResourceState.Active
 
         start(ctx)
     }
 
-    override fun close() {
-        cancel()
-        state = SimResourceState.Stopped
-    }
-
     final override fun interrupt() {
         ctx?.interrupt()
     }
@@ -121,10 +115,6 @@ public abstract class SimAbstractResourceProvider(
             this.ctx = null
             ctx.close()
         }
-
-        if (state != SimResourceState.Stopped) {
-            state = SimResourceState.Pending
-        }
     }
 
     override fun toString(): String = "SimAbstractResourceProvider[capacity=$capacity]"
diff --git a/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceCloseableProvider.kt b/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceCloseableProvider.kt
new file mode 100644
index 00000000..bce8274b
--- /dev/null
+++ b/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceCloseableProvider.kt
@@ -0,0 +1,37 @@
+/*
+ * 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.resources
+
+/**
+ * A [SimResourceProvider] that has a controllable and limited lifetime.
+ *
+ * This interface is used to signal that the resource provider may be closed and not reused after that point.
+ */
+public interface SimResourceCloseableProvider : SimResourceProvider, AutoCloseable {
+    /**
+     * End the lifetime of the resource provider.
+     *
+     * This operation cancels the existing resource consumer and prevents the resource provider from being reused.
+     */
+    public override fun close()
+}
diff --git a/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceDistributor.kt b/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceDistributor.kt
index e0333ff9..6bfbfc99 100644
--- a/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceDistributor.kt
+++ b/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceDistributor.kt
@@ -29,10 +29,10 @@ public interface SimResourceDistributor : SimResourceConsumer {
     /**
      * The output resource providers to which resource consumers can be attached.
      */
-    public val outputs: Set<SimResourceProvider>
+    public val outputs: Set<SimResourceCloseableProvider>
 
     /**
      * Create a new output for the distributor.
      */
-    public fun newOutput(): SimResourceProvider
+    public fun newOutput(): SimResourceCloseableProvider
 }
diff --git a/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceDistributorMaxMin.kt b/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceDistributorMaxMin.kt
index be9e89fb..f7c5c5d7 100644
--- a/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceDistributorMaxMin.kt
+++ b/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceDistributorMaxMin.kt
@@ -32,7 +32,7 @@ public class SimResourceDistributorMaxMin(
     private val interpreter: SimResourceInterpreter,
     private val parent: SimResourceSystem? = null
 ) : SimResourceDistributor {
-    override val outputs: Set<SimResourceProvider>
+    override val outputs: Set<SimResourceCloseableProvider>
         get() = _outputs
     private val _outputs = mutableSetOf<Output>()
 
@@ -57,7 +57,7 @@ public class SimResourceDistributorMaxMin(
     private var totalAllocatedSpeed = 0.0
 
     /* SimResourceDistributor */
-    override fun newOutput(): SimResourceProvider {
+    override fun newOutput(): SimResourceCloseableProvider {
         val provider = Output(ctx?.capacity ?: 0.0)
         _outputs.add(provider)
         return provider
@@ -178,7 +178,16 @@ public class SimResourceDistributorMaxMin(
     /**
      * An internal [SimResourceProvider] implementation for switch outputs.
      */
-    private inner class Output(capacity: Double) : SimAbstractResourceProvider(interpreter, parent, capacity), SimResourceProviderLogic, Comparable<Output> {
+    private inner class Output(capacity: Double) :
+        SimAbstractResourceProvider(interpreter, parent, capacity),
+        SimResourceCloseableProvider,
+        SimResourceProviderLogic,
+        Comparable<Output> {
+        /**
+         * A flag to indicate that the output is closed.
+         */
+        private var isClosed: Boolean = false
+
         /**
          * The current command that is processed by the resource.
          */
@@ -209,6 +218,8 @@ public class SimResourceDistributorMaxMin(
         override fun createLogic(): SimResourceProviderLogic = this
 
         override fun start(ctx: SimResourceControllableContext) {
+            check(!isClosed) { "Cannot re-use closed output" }
+
             activeOutputs += this
 
             interpreter.batch {
@@ -219,13 +230,9 @@ public class SimResourceDistributorMaxMin(
         }
 
         override fun close() {
-            val state = state
-
-            super.close()
-
-            if (state != SimResourceState.Stopped) {
-                _outputs.remove(this)
-            }
+            isClosed = true
+            cancel()
+            _outputs.remove(this)
         }
 
         /* SimResourceProviderLogic */
diff --git a/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceProvider.kt b/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceProvider.kt
index f709ca17..b68b7261 100644
--- a/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceProvider.kt
+++ b/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceProvider.kt
@@ -29,11 +29,11 @@ import kotlin.coroutines.resumeWithException
 /**
  * A [SimResourceProvider] provides a resource that can be consumed by a [SimResourceConsumer].
  */
-public interface SimResourceProvider : AutoCloseable {
+public interface SimResourceProvider {
     /**
-     * The state of the resource.
+     * A flag to indicate that the resource provider is currently being consumed by a [SimResourceConsumer].
      */
-    public val state: SimResourceState
+    public val isActive: Boolean
 
     /**
      * The resource capacity available at this instant.
@@ -71,13 +71,6 @@ public interface SimResourceProvider : AutoCloseable {
      * Cancel the current resource consumer. If there is no consumer active, this operation will be a no-op.
      */
     public fun cancel()
-
-    /**
-     * End the lifetime of the resource.
-     *
-     * This operation terminates the existing resource consumer.
-     */
-    public override fun close()
 }
 
 /**
diff --git a/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceSwitch.kt b/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceSwitch.kt
index e224285e..f6e7b22f 100644
--- a/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceSwitch.kt
+++ b/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceSwitch.kt
@@ -29,7 +29,7 @@ public interface SimResourceSwitch : AutoCloseable {
     /**
      * The output resource providers to which resource consumers can be attached.
      */
-    public val outputs: Set<SimResourceProvider>
+    public val outputs: Set<SimResourceCloseableProvider>
 
     /**
      * The input resources that will be switched between the output providers.
@@ -44,7 +44,7 @@ public interface SimResourceSwitch : AutoCloseable {
     /**
      * Create a new output on the switch.
      */
-    public fun newOutput(): SimResourceProvider
+    public fun newOutput(): SimResourceCloseableProvider
 
     /**
      * Add the specified [input] to the switch.
diff --git a/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceSwitchExclusive.kt b/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceSwitchExclusive.kt
index 2950af80..4ff741ed 100644
--- a/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceSwitchExclusive.kt
+++ b/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceSwitchExclusive.kt
@@ -35,7 +35,7 @@ public class SimResourceSwitchExclusive : SimResourceSwitch {
     private var isClosed: Boolean = false
 
     private val _outputs = mutableSetOf<Provider>()
-    override val outputs: Set<SimResourceProvider>
+    override val outputs: Set<SimResourceCloseableProvider>
         get() = _outputs
 
     private val availableResources = ArrayDeque<SimResourceTransformer>()
@@ -61,7 +61,7 @@ public class SimResourceSwitchExclusive : SimResourceSwitch {
         override fun toString(): String = "SimResourceCounters[demand=$demand,actual=$actual,overcommit=$overcommit]"
     }
 
-    override fun newOutput(): SimResourceProvider {
+    override fun newOutput(): SimResourceCloseableProvider {
         check(!isClosed) { "Switch has been closed" }
         check(availableResources.isNotEmpty()) { "No capacity to serve request" }
         val forwarder = availableResources.poll()
@@ -101,7 +101,7 @@ public class SimResourceSwitchExclusive : SimResourceSwitch {
         _inputs.forEach(SimResourceProvider::cancel)
     }
 
-    private inner class Provider(private val forwarder: SimResourceTransformer) : SimResourceProvider by forwarder {
+    private inner class Provider(private val forwarder: SimResourceTransformer) : SimResourceCloseableProvider, SimResourceProvider by forwarder {
         override fun close() {
             // We explicitly do not close the forwarder here in order to re-use it across output resources.
             _outputs -= this
diff --git a/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceSwitchMaxMin.kt b/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceSwitchMaxMin.kt
index 684a1b52..50d58798 100644
--- a/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceSwitchMaxMin.kt
+++ b/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceSwitchMaxMin.kt
@@ -33,7 +33,7 @@ public class SimResourceSwitchMaxMin(
     /**
      * The output resource providers to which resource consumers can be attached.
      */
-    override val outputs: Set<SimResourceProvider>
+    override val outputs: Set<SimResourceCloseableProvider>
         get() = distributor.outputs
 
     /**
@@ -70,7 +70,7 @@ public class SimResourceSwitchMaxMin(
     /**
      * Add an output to the switch.
      */
-    override fun newOutput(): SimResourceProvider {
+    override fun newOutput(): SimResourceCloseableProvider {
         check(!isClosed) { "Switch has been closed" }
 
         return distributor.newOutput()
@@ -88,7 +88,7 @@ public class SimResourceSwitchMaxMin(
     override fun close() {
         if (!isClosed) {
             isClosed = true
-            aggregator.close()
+            aggregator.cancel()
         }
     }
 }
diff --git a/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceTransformer.kt b/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceTransformer.kt
index fd3d1230..cec27e1c 100644
--- a/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceTransformer.kt
+++ b/opendc-simulator/opendc-simulator-resources/src/main/kotlin/org/opendc/simulator/resources/SimResourceTransformer.kt
@@ -33,7 +33,7 @@ import org.opendc.simulator.resources.impl.SimResourceCountersImpl
 public class SimResourceTransformer(
     private val isCoupled: Boolean = false,
     private val transform: (SimResourceContext, SimResourceCommand) -> SimResourceCommand
-) : SimResourceFlow {
+) : SimResourceFlow, AutoCloseable {
     /**
      * The [SimResourceContext] in which the forwarder runs.
      */
@@ -49,11 +49,8 @@ public class SimResourceTransformer(
      */
     private var hasDelegateStarted: Boolean = false
 
-    /**
-     * The state of the forwarder.
-     */
-    override var state: SimResourceState = SimResourceState.Pending
-        private set
+    override val isActive: Boolean
+        get() = delegate != null
 
     override val capacity: Double
         get() = ctx?.capacity ?: 0.0
@@ -69,9 +66,8 @@ public class SimResourceTransformer(
     private val _counters = SimResourceCountersImpl()
 
     override fun startConsumer(consumer: SimResourceConsumer) {
-        check(state == SimResourceState.Pending) { "Resource is in invalid state" }
+        check(delegate == null) { "Resource transformer already active" }
 
-        state = SimResourceState.Active
         delegate = consumer
 
         // Interrupt the provider to replace the consumer
@@ -86,19 +82,18 @@ public class SimResourceTransformer(
         val delegate = delegate
         val ctx = ctx
 
-        state = SimResourceState.Pending
-
-        if (delegate != null && ctx != null) {
+        if (delegate != null) {
             this.delegate = null
-            delegate.onEvent(ctx, SimResourceEvent.Exit)
+
+            if (ctx != null) {
+                delegate.onEvent(ctx, SimResourceEvent.Exit)
+            }
         }
     }
 
     override fun close() {
         val ctx = ctx
 
-        state = SimResourceState.Stopped
-
         if (ctx != null) {
             this.ctx = null
             ctx.interrupt()
@@ -114,9 +109,7 @@ public class SimResourceTransformer(
 
         updateCounters(ctx)
 
-        return if (state == SimResourceState.Stopped) {
-            SimResourceCommand.Exit
-        } else if (delegate != null) {
+        return if (delegate != null) {
             val command = transform(ctx, delegate.onNext(ctx))
 
             _work = if (command is SimResourceCommand.Consume) command.work else 0.0
@@ -128,7 +121,7 @@ public class SimResourceTransformer(
 
                 delegate.onEvent(ctx, SimResourceEvent.Exit)
 
-                if (isCoupled || state == SimResourceState.Stopped)
+                if (isCoupled)
                     SimResourceCommand.Exit
                 else
                     onNext(ctx)
@@ -184,10 +177,6 @@ public class SimResourceTransformer(
     private fun reset() {
         delegate = null
         hasDelegateStarted = false
-
-        if (state != SimResourceState.Stopped) {
-            state = SimResourceState.Pending
-        }
     }
 
     /**