feat(sim/compute): Add support for snapshotting workloads

This change updates the interface of `SimWorkload` to support
snapshotting workloads. We introduce a new method `snapshot()` to this
interface which returns a new `SimWorkload` that can be started at a
later point in time and on another `SimMachine`, which continues
progress from the moment the workload was snapshotted.

8 files changed, 120 insertions, 9 deletions

diff --git a/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/SimAbstractMachine.java b/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/SimAbstractMachine.java
index 40c219ed..f684c54d 100644
--- a/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/SimAbstractMachine.java
+++ b/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/SimAbstractMachine.java
@@ -131,6 +131,11 @@ public abstract class SimAbstractMachine implements SimMachine {
         }
 
         @Override
+        public SimWorkload snapshot() {
+            return workload.snapshot();
+        }
+
+        @Override
         public void reset() {
             final FlowGraph graph = getMemory().getInput().getGraph();
 
diff --git a/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/SimMachineContext.java b/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/SimMachineContext.java
index 0f7d4c8b..bce5c0a8 100644
--- a/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/SimMachineContext.java
+++ b/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/SimMachineContext.java
@@ -69,6 +69,13 @@ public interface SimMachineContext {
     List<? extends SimStorageInterface> getStorageInterfaces();
 
     /**
+     * Create a snapshot of the {@link SimWorkload} running on this machine.
+     *
+     * @throws UnsupportedOperationException if the workload does not support snapshotting.
+     */
+    SimWorkload snapshot();
+
+    /**
      * Reset all resources of the machine.
      */
     void reset();
diff --git a/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/kernel/SimHypervisor.java b/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/kernel/SimHypervisor.java
index f03a0c20..4ebcba71 100644
--- a/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/kernel/SimHypervisor.java
+++ b/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/kernel/SimHypervisor.java
@@ -240,6 +240,11 @@ public final class SimHypervisor implements SimWorkload {
         }
     }
 
+    @Override
+    public SimWorkload snapshot() {
+        throw new UnsupportedOperationException("Unable to snapshot hypervisor");
+    }
+
     /**
      * The context which carries the state when the hypervisor is running on a machine.
      */
diff --git a/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/workload/SimChainWorkload.java b/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/workload/SimChainWorkload.java
index f838328b..7480b3c0 100644
--- a/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/workload/SimChainWorkload.java
+++ b/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/workload/SimChainWorkload.java
@@ -44,9 +44,20 @@ final class SimChainWorkload implements SimWorkload {
      * Construct a {@link SimChainWorkload} instance.
      *
      * @param workloads The workloads to chain.
+     * @param activeWorkloadIndex The index of the active workload.
      */
-    SimChainWorkload(SimWorkload... workloads) {
+    SimChainWorkload(SimWorkload[] workloads, int activeWorkloadIndex) {
         this.workloads = workloads;
+        this.activeWorkloadIndex = activeWorkloadIndex;
+    }
+
+    /**
+     * Construct a {@link SimChainWorkload} instance.
+     *
+     * @param workloads The workloads to chain.
+     */
+    SimChainWorkload(SimWorkload... workloads) {
+        this(workloads, 0);
     }
 
     @Override
@@ -79,6 +90,19 @@ final class SimChainWorkload implements SimWorkload {
         tryThrow(context.doStop(workloads[activeWorkloadIndex]));
     }
 
+    @Override
+    public SimChainWorkload snapshot() {
+        final int activeWorkloadIndex = this.activeWorkloadIndex;
+        final SimWorkload[] workloads = this.workloads;
+        final SimWorkload[] newWorkloads = new SimWorkload[workloads.length - activeWorkloadIndex];
+
+        for (int i = 0; i < newWorkloads.length; i++) {
+            newWorkloads[i] = workloads[activeWorkloadIndex + i].snapshot();
+        }
+
+        return new SimChainWorkload(newWorkloads, 0);
+    }
+
     /**
      * A {@link SimMachineContext} that intercepts the shutdown calls.
      */
@@ -120,6 +144,12 @@ final class SimChainWorkload implements SimWorkload {
         }
 
         @Override
+        public SimWorkload snapshot() {
+            final SimWorkload workload = workloads[activeWorkloadIndex];
+            return workload.snapshot();
+        }
+
+        @Override
         public void reset() {
             ctx.reset();
         }
diff --git a/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/workload/SimFlopsWorkload.java b/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/workload/SimFlopsWorkload.java
index f3efbebb..839856bb 100644
--- a/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/workload/SimFlopsWorkload.java
+++ b/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/workload/SimFlopsWorkload.java
@@ -60,6 +60,7 @@ public class SimFlopsWorkload implements SimWorkload, FlowStageLogic {
 
         this.flops = flops;
         this.utilization = utilization;
+        this.remainingAmount = flops;
     }
 
     @Override
@@ -98,8 +99,13 @@ public class SimFlopsWorkload implements SimWorkload, FlowStageLogic {
     }
 
     @Override
-    public String toString() {
-        return "SimFlopsWorkload[FLOPs=" + flops + ",utilization=" + utilization + "]";
+    public SimFlopsWorkload snapshot() {
+        final FlowStage stage = this.stage;
+        if (stage != null) {
+            stage.sync();
+        }
+
+        return new SimFlopsWorkload((long) remainingAmount, utilization);
     }
 
     @Override
@@ -138,4 +144,9 @@ public class SimFlopsWorkload implements SimWorkload, FlowStageLogic {
 
         return now + duration;
     }
+
+    @Override
+    public String toString() {
+        return "SimFlopsWorkload[FLOPs=" + flops + ",utilization=" + utilization + "]";
+    }
 }
diff --git a/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/workload/SimRuntimeWorkload.java b/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/workload/SimRuntimeWorkload.java
index 194efafd..9c9f4788 100644
--- a/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/workload/SimRuntimeWorkload.java
+++ b/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/workload/SimRuntimeWorkload.java
@@ -59,6 +59,7 @@ public class SimRuntimeWorkload implements SimWorkload, FlowStageLogic {
 
         this.duration = duration;
         this.utilization = utilization;
+        this.remainingDuration = duration;
     }
 
     @Override
@@ -98,6 +99,16 @@ public class SimRuntimeWorkload implements SimWorkload, FlowStageLogic {
     }
 
     @Override
+    public SimRuntimeWorkload snapshot() {
+        final FlowStage stage = this.stage;
+        if (stage != null) {
+            stage.sync();
+        }
+
+        return new SimRuntimeWorkload(remainingDuration, utilization);
+    }
+
+    @Override
     public long onUpdate(FlowStage ctx, long now) {
         long lastUpdate = this.lastUpdate;
         this.lastUpdate = now;
diff --git a/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/workload/SimTrace.java b/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/workload/SimTrace.java
index 12a567ff..1d8667d5 100644
--- a/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/workload/SimTrace.java
+++ b/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/workload/SimTrace.java
@@ -71,7 +71,7 @@ public final class SimTrace {
      * @param offset The offset for the timestamps.
      */
     public SimWorkload createWorkload(long offset) {
-        return new Workload(offset, usageCol, deadlineCol, coresCol, size);
+        return new Workload(offset, usageCol, deadlineCol, coresCol, size, 0);
     }
 
     /**
@@ -211,22 +211,24 @@ public final class SimTrace {
         private final long[] deadlineCol;
         private final int[] coresCol;
         private final int size;
+        private final int index;
 
-        private Workload(long offset, double[] usageCol, long[] deadlineCol, int[] coresCol, int size) {
+        private Workload(long offset, double[] usageCol, long[] deadlineCol, int[] coresCol, int size, int index) {
             this.offset = offset;
             this.usageCol = usageCol;
             this.deadlineCol = deadlineCol;
             this.coresCol = coresCol;
             this.size = size;
+            this.index = index;
         }
 
         @Override
         public void onStart(SimMachineContext ctx) {
             final WorkloadStageLogic logic;
             if (ctx.getCpus().size() == 1) {
-                logic = new SingleWorkloadLogic(ctx, offset, usageCol, deadlineCol, size);
+                logic = new SingleWorkloadLogic(ctx, offset, usageCol, deadlineCol, size, index);
             } else {
-                logic = new MultiWorkloadLogic(ctx, offset, usageCol, deadlineCol, coresCol, size);
+                logic = new MultiWorkloadLogic(ctx, offset, usageCol, deadlineCol, coresCol, size, index);
             }
             this.logic = logic;
         }
@@ -240,6 +242,18 @@ public final class SimTrace {
                 logic.getStage().close();
             }
         }
+
+        @Override
+        public SimWorkload snapshot() {
+            final WorkloadStageLogic logic = this.logic;
+            int index = this.index;
+
+            if (logic != null) {
+                index = logic.getIndex();
+            }
+
+            return new Workload(offset, usageCol, deadlineCol, coresCol, size, index);
+        }
     }
 
     /**
@@ -250,6 +264,11 @@ public final class SimTrace {
          * Return the {@link FlowStage} belonging to this instance.
          */
         FlowStage getStage();
+
+        /**
+         * Return the current index of the workload.
+         */
+        int getIndex();
     }
 
     /**
@@ -268,12 +287,13 @@ public final class SimTrace {
         private final SimMachineContext ctx;
 
         private SingleWorkloadLogic(
-                SimMachineContext ctx, long offset, double[] usageCol, long[] deadlineCol, int size) {
+                SimMachineContext ctx, long offset, double[] usageCol, long[] deadlineCol, int size, int index) {
             this.ctx = ctx;
             this.offset = offset;
             this.usageCol = usageCol;
             this.deadlineCol = deadlineCol;
             this.size = size;
+            this.index = index;
 
             final FlowGraph graph = ctx.getGraph();
             final List<? extends SimProcessingUnit> cpus = ctx.getCpus();
@@ -315,6 +335,11 @@ public final class SimTrace {
             return stage;
         }
 
+        @Override
+        public int getIndex() {
+            return index;
+        }
+
         /**
          * Helper method to stop the execution of the workload.
          */
@@ -346,13 +371,20 @@ public final class SimTrace {
         private final SimMachineContext ctx;
 
         private MultiWorkloadLogic(
-                SimMachineContext ctx, long offset, double[] usageCol, long[] deadlineCol, int[] coresCol, int size) {
+                SimMachineContext ctx,
+                long offset,
+                double[] usageCol,
+                long[] deadlineCol,
+                int[] coresCol,
+                int size,
+                int index) {
             this.ctx = ctx;
             this.offset = offset;
             this.usageCol = usageCol;
             this.deadlineCol = deadlineCol;
             this.coresCol = coresCol;
             this.size = size;
+            this.index = index;
 
             final FlowGraph graph = ctx.getGraph();
             final List<? extends SimProcessingUnit> cpus = ctx.getCpus();
@@ -418,5 +450,10 @@ public final class SimTrace {
         public FlowStage getStage() {
             return stage;
         }
+
+        @Override
+        public int getIndex() {
+            return index;
+        }
     }
 }
diff --git a/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/workload/SimWorkload.java b/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/workload/SimWorkload.java
index 7be51265..cad324fb 100644
--- a/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/workload/SimWorkload.java
+++ b/opendc-simulator/opendc-simulator-compute/src/main/java/org/opendc/simulator/compute/workload/SimWorkload.java
@@ -45,4 +45,9 @@ public interface SimWorkload {
      * @param ctx The execution context in which the machine runs.
      */
     void onStop(SimMachineContext ctx);
+
+    /**
+     * Create a snapshot of this workload.
+     */
+    SimWorkload snapshot();
 }