Implement scheduling system with parallel execution support and dummy job systems

Nerfed.Editor/Program.cs

@@ -2,7 +2,9 @@
 using Nerfed.Editor.Systems;
 using Nerfed.Runtime;
 using Nerfed.Runtime.Components;
+using Nerfed.Runtime.Scheduling;
 using Nerfed.Runtime.Systems;
+using Nerfed.Runtime.Systems.Synthetic;
 using Nerfed.Runtime.Util;
 using System.Numerics;
 
@@ -12,10 +14,22 @@ internal class Program
 {
     private static readonly World world = new World();
     private static List<MoonTools.ECS.System> systems = new List<MoonTools.ECS.System>();
+    private static SystemScheduler scheduler;
     public static List<MoonTools.ECS.System> editorSystems = new List<MoonTools.ECS.System>();
+    private static bool enableDummySchedulerHarness;
+    private static bool enableParallelSystemExecution;
 
     private static void Main(string[] args)
     {
+        enableDummySchedulerHarness = args.Contains("--dummy-scheduler-test", StringComparer.OrdinalIgnoreCase);
+        enableParallelSystemExecution = args.Contains("--parallel-systems", StringComparer.OrdinalIgnoreCase);
+
+        scheduler = new SystemScheduler(new SystemSchedulerOptions
+        {
+            EnableParallelSystemExecution = enableParallelSystemExecution,
+            StrictDependencyValidation = true,
+        });
+
         Engine.OnInitialize += HandleOnInitialize;
         Engine.OnUpdate += HandleOnUpdate;
         Engine.OnRender += HandleOnRender;
@@ -27,7 +41,42 @@ internal class Program
     private static void HandleOnInitialize()
     {
         //systems.Add(new ParentSystem(world));
-        systems.Add(new LocalToWorldSystem(world));
+        LocalToWorldSystem localToWorldSystem = new LocalToWorldSystem(world);
+        systems.Add(localToWorldSystem);
+        scheduler.Register(localToWorldSystem, SystemSchedulePhase.Simulation);
+
+        if (enableDummySchedulerHarness)
+        {
+            DummyLongJobSharedState sharedState = new DummyLongJobSharedState();
+
+            // Producer starts long work, middle system burns time on main thread, consumer acts as a barrier.
+            DummyLongJobProducerSystem producer = new DummyLongJobProducerSystem(
+                world,
+                sharedState,
+                JobSystem.Default,
+                TimeSpan.FromMilliseconds(6),
+                DummyWorkloadMode.Compute,
+                JobDeadlineMode.FrameCritical);
+            systems.Add(producer);
+            scheduler.Register(producer, SystemSchedulePhase.Simulation);
+
+            DummyMainThreadWorkSystem mainThreadWork = new DummyMainThreadWorkSystem(
+                world,
+                TimeSpan.FromMilliseconds(2),
+                DummyWorkloadMode.Compute,
+                nameof(DummyMainThreadWorkSystem));
+            systems.Add(mainThreadWork);
+            scheduler.Register(mainThreadWork, SystemSchedulePhase.Simulation);
+
+            DummyLongJobConsumerSystem consumer = new DummyLongJobConsumerSystem(
+                world,
+                sharedState,
+                JobSystem.Default,
+                requireCompletion: true);
+            systems.Add(consumer);
+            scheduler.Register(consumer, SystemSchedulePhase.LateSimulation, nameof(DummyLongJobProducerSystem));
+        }
+
         editorSystems.Add(new EditorProfilerWindow(world));
         editorSystems.Add(new EditorHierarchyWindow(world));
 #if DEBUG
@@ -72,10 +121,9 @@ internal class Program
 
     private static void HandleOnUpdate()
     {
-        foreach (MoonTools.ECS.System system in systems)
+        using (new ProfilerScope("SystemScheduler.Execute"))
         {
-            using ProfilerScope scope = new(system.GetType().Name);
-            system.Update(Engine.Timestep);
+            scheduler.Execute(Engine.Timestep);
         }
 
         using (new ProfilerScope("EditorGui.Update"))

Nerfed.Runtime/JobSystem.cs

@@ -1,7 +1,67 @@
+using System.Collections.Concurrent;
 using System.Diagnostics;
+using System.Runtime.ExceptionServices;
 
 namespace Nerfed.Runtime;
 
+public enum JobDeadlineMode
+{
+    FrameCritical,
+    Deferred,
+}
+
+public enum JobExecutionStatus
+{
+    Invalid,
+    Queued,
+    Running,
+    Completed,
+    Faulted,
+    Canceled,
+}
+
+public readonly struct JobHandle : IEquatable<JobHandle>
+{
+    internal readonly int id;
+
+    internal JobHandle(int id)
+    {
+        this.id = id;
+    }
+
+    public bool IsValid => id > 0;
+
+    public bool Equals(JobHandle other)
+    {
+        return id == other.id;
+    }
+
+    public override bool Equals(object obj)
+    {
+        return obj is JobHandle other && Equals(other);
+    }
+
+    public override int GetHashCode()
+    {
+        return id;
+    }
+
+    public static bool operator ==(JobHandle left, JobHandle right)
+    {
+        return left.Equals(right);
+    }
+
+    public static bool operator !=(JobHandle left, JobHandle right)
+    {
+        return !left.Equals(right);
+    }
+
+    public override string ToString()
+    {
+        return IsValid ? $"JobHandle({id})" : "JobHandle(Invalid)";
+    }
+}
+
 public sealed class JobSystem : IDisposable
 {
     public static readonly JobSystem Default = new JobSystem();
@@ -9,6 +69,13 @@ public sealed class JobSystem : IDisposable
     private Thread[] workers;
     private SemaphoreSlim startSignal;
     private CountdownEvent completionEvent;
+
+    private Thread[] asyncWorkers;
+    private SemaphoreSlim asyncSignal;
+    private ConcurrentQueue<int> asyncQueue;
+    private ConcurrentDictionary<int, AsyncJobState> asyncJobStates;
+    private int nextAsyncJobId;
+
     private volatile bool running;
 
     // Shared per-dispatch state written by main thread before workers wake.
@@ -16,10 +83,41 @@ public sealed class JobSystem : IDisposable
     private int workCount;
     private int nextIndex; // grabbed with Interlocked.Increment for work-stealing
 
+    private sealed class AsyncJobState : IDisposable
+    {
+        public readonly Action Action;
+        public readonly JobDeadlineMode Deadline;
+        public readonly string Name;
+        public readonly ManualResetEventSlim Completion = new(false);
+
+        public ExceptionDispatchInfo CapturedException;
+        public volatile JobExecutionStatus Status;
+        public volatile bool CancellationRequested;
+
+        public AsyncJobState(Action action, JobDeadlineMode deadline, string name)
+        {
+            Action = action;
+            Deadline = deadline;
+            Name = name;
+            Status = JobExecutionStatus.Queued;
+        }
+
+        public bool IsTerminal =>
+            Status == JobExecutionStatus.Completed ||
+            Status == JobExecutionStatus.Faulted ||
+            Status == JobExecutionStatus.Canceled;
+
+        public void Dispose()
+        {
+            Completion.Dispose();
+        }
+    }
+
     public int WorkerCount => workers?.Length ?? 0;
+    public int AsyncWorkerCount => asyncWorkers?.Length ?? 0;
     public bool IsInitialized => workers != null;
 
-    public void Initialize(int threadCount = -1)
+    public void Initialize(int threadCount = -1, int asyncThreadCount = -1)
     {
         if (IsInitialized)
         {
@@ -33,7 +131,16 @@ public sealed class JobSystem : IDisposable
         running = true;
         startSignal = new SemaphoreSlim(0);
         completionEvent = new CountdownEvent(1);
+        asyncSignal = new SemaphoreSlim(0);
         workers = new Thread[threadCount];
+        asyncQueue = new ConcurrentQueue<int>();
+        asyncJobStates = new ConcurrentDictionary<int, AsyncJobState>();
+
+        asyncThreadCount = asyncThreadCount < 0
+            ? Math.Max(1, Environment.ProcessorCount >= 8 ? 2 : 1)
+            : Math.Max(0, asyncThreadCount);
+
+        asyncWorkers = new Thread[asyncThreadCount];
 
         for (int i = 0; i < threadCount; i++)
         {
@@ -44,6 +151,98 @@ public sealed class JobSystem : IDisposable
             };
             workers[i].Start();
         }
+
+        for (int i = 0; i < asyncThreadCount; i++)
+        {
+            asyncWorkers[i] = new Thread(AsyncWorkerLoop)
+            {
+                IsBackground = true,
+                Name = $"AsyncJob-{i}",
+            };
+            asyncWorkers[i].Start();
+        }
+    }
+
+    public JobHandle Submit(Action action, JobDeadlineMode deadline = JobDeadlineMode.Deferred, string name = "")
+    {
+        ArgumentNullException.ThrowIfNull(action);
+
+        if (!running)
+        {
+            throw new InvalidOperationException("JobSystem is not running. Call Initialize before submitting jobs.");
+        }
+
+        int id = Interlocked.Increment(ref nextAsyncJobId);
+        var state = new AsyncJobState(action, deadline, name ?? string.Empty);
+
+        if (!asyncJobStates.TryAdd(id, state))
+        {
+            state.Dispose();
+            throw new InvalidOperationException($"Failed to register async job {id}.");
+        }
+
+        asyncQueue.Enqueue(id);
+        asyncSignal.Release();
+        return new JobHandle(id);
+    }
+
+    public JobExecutionStatus GetStatus(JobHandle handle)
+    {
+        if (!handle.IsValid)
+        {
+            return JobExecutionStatus.Invalid;
+        }
+
+        return asyncJobStates.TryGetValue(handle.id, out AsyncJobState state)
+            ? state.Status
+            : JobExecutionStatus.Invalid;
+    }
+
+    public bool IsCompleted(JobHandle handle)
+    {
+        return GetStatus(handle) is JobExecutionStatus.Completed or JobExecutionStatus.Faulted or JobExecutionStatus.Canceled;
+    }
+
+    public bool Cancel(JobHandle handle)
+    {
+        if (!handle.IsValid || !asyncJobStates.TryGetValue(handle.id, out AsyncJobState state))
+        {
+            return false;
+        }
+
+        state.CancellationRequested = true;
+        return true;
+    }
+
+    public void Wait(JobHandle handle)
+    {
+        if (!handle.IsValid || !asyncJobStates.TryGetValue(handle.id, out AsyncJobState state))
+        {
+            throw new InvalidOperationException($"Unknown job handle {handle}.");
+        }
+
+        state.Completion.Wait();
+
+        if (state.Status == JobExecutionStatus.Faulted)
+        {
+            state.CapturedException?.Throw();
+        }
+    }
+
+    public bool TryForget(JobHandle handle)
+    {
+        if (!handle.IsValid || !asyncJobStates.TryGetValue(handle.id, out AsyncJobState state) || !state.IsTerminal)
+        {
+            return false;
+        }
+
+        if (asyncJobStates.TryRemove(handle.id, out AsyncJobState removedState))
+        {
+            removedState.Dispose();
+            return true;
+        }
+
+        return false;
     }
 
     public void Dispatch(int count, Action<int> action)
@@ -79,8 +278,30 @@ public sealed class JobSystem : IDisposable
         foreach (Thread t in workers)
             t.Join();
 
+        for (int i = 0; i < asyncWorkers.Length; i++)
+        {
+            asyncSignal.Release();
+        }
+
+        foreach (Thread t in asyncWorkers)
+        {
+            t.Join();
+        }
+
         completionEvent.Dispose();
         startSignal.Dispose();
+        asyncSignal.Dispose();
+
+        foreach (KeyValuePair<int, AsyncJobState> pair in asyncJobStates)
+        {
+            pair.Value.Dispose();
+        }
+
+        asyncJobStates.Clear();
+
+        asyncWorkers = null;
+        asyncQueue = null;
+        asyncJobStates = null;
         workers = null;
     }
 
@@ -106,4 +327,52 @@ public sealed class JobSystem : IDisposable
             completionEvent.Signal();
         }
     }
+
+    private void AsyncWorkerLoop()
+    {
+        while (true)
+        {
+            asyncSignal.Wait();
+
+            if (!running)
+            {
+                return;
+            }
+
+            if (!asyncQueue.TryDequeue(out int jobId))
+            {
+                continue;
+            }
+
+            if (!asyncJobStates.TryGetValue(jobId, out AsyncJobState state))
+            {
+                continue;
+            }
+
+            if (state.CancellationRequested)
+            {
+                state.Status = JobExecutionStatus.Canceled;
+                state.Completion.Set();
+                continue;
+            }
+
+            state.Status = JobExecutionStatus.Running;
+            try
+            {
+                state.Action();
+                state.Status = state.CancellationRequested
+                    ? JobExecutionStatus.Canceled
+                    : JobExecutionStatus.Completed;
+            }
+            catch (Exception ex)
+            {
+                state.CapturedException = ExceptionDispatchInfo.Capture(ex);
+                state.Status = JobExecutionStatus.Faulted;
+            }
+            finally
+            {
+                state.Completion.Set();
+            }
+        }
+    }
 }

Nerfed.Runtime/Scheduling/IParallelSystemMetadata.cs

@@ -0,0 +1,7 @@
+namespace Nerfed.Runtime.Scheduling;
+
+public interface IParallelSystemMetadata
+{
+    string ScheduleName { get; }
+    SystemAccessDeclaration AccessDeclaration { get; }
+}

Nerfed.Runtime/Scheduling/SystemAccessDeclaration.cs

@@ -0,0 +1,69 @@
+namespace Nerfed.Runtime.Scheduling;
+
+public enum SystemAccessMode
+{
+    Read,
+    WriteExisting,
+    StructuralWrite,
+}
+
+public readonly struct ComponentAccess
+{
+    public ComponentAccess(Type componentType, SystemAccessMode mode)
+    {
+        ComponentType = componentType;
+        Mode = mode;
+    }
+
+    public Type ComponentType { get; }
+    public SystemAccessMode Mode { get; }
+}
+
+public readonly struct SystemAccessDeclaration
+{
+    private readonly ComponentAccess[] accesses;
+
+    public static readonly SystemAccessDeclaration Empty = new(Array.Empty<ComponentAccess>());
+
+    public SystemAccessDeclaration(params ComponentAccess[] accesses)
+    {
+        this.accesses = accesses ?? Array.Empty<ComponentAccess>();
+    }
+
+    public ReadOnlySpan<ComponentAccess> Accesses => accesses ?? Array.Empty<ComponentAccess>();
+
+    public bool ConflictsWith(in SystemAccessDeclaration other)
+    {
+        ReadOnlySpan<ComponentAccess> left = Accesses;
+        ReadOnlySpan<ComponentAccess> right = other.Accesses;
+
+        for (int i = 0; i < left.Length; i++)
+        {
+            for (int j = 0; j < right.Length; j++)
+            {
+                if (left[i].Mode == SystemAccessMode.StructuralWrite || right[j].Mode == SystemAccessMode.StructuralWrite)
+                {
+                    return true;
+                }
+
+                if (left[i].ComponentType != right[j].ComponentType)
+                {
+                    continue;
+                }
+
+                if (left[i].Mode == SystemAccessMode.Read && right[j].Mode == SystemAccessMode.Read)
+                {
+                    continue;
+                }
+
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    public static ComponentAccess Read<T>() where T : unmanaged => new(typeof(T), SystemAccessMode.Read);
+    public static ComponentAccess WriteExisting<T>() where T : unmanaged => new(typeof(T), SystemAccessMode.WriteExisting);
+    public static ComponentAccess StructuralWrite<T>() where T : unmanaged => new(typeof(T), SystemAccessMode.StructuralWrite);
+}

Nerfed.Runtime/Scheduling/SystemScheduleEntry.cs

@@ -0,0 +1,37 @@
+using MoonTools.ECS;
+
+namespace Nerfed.Runtime.Scheduling;
+
+public sealed class SystemScheduleEntry
+{
+    public SystemScheduleEntry(
+        MoonTools.ECS.System system,
+        SystemSchedulePhase phase,
+        string[] dependsOn,
+        int registrationIndex)
+    {
+        System = system;
+        Phase = phase;
+        DependsOn = dependsOn ?? Array.Empty<string>();
+        RegistrationIndex = registrationIndex;
+
+        if (system is IParallelSystemMetadata metadata)
+        {
+            Name = metadata.ScheduleName;
+            Access = metadata.AccessDeclaration;
+        }
+        else
+        {
+            Name = system.GetType().Name;
+            // Unknown systems are treated as structural to preserve safety until metadata is declared.
+            Access = new SystemAccessDeclaration(new ComponentAccess(typeof(object), SystemAccessMode.StructuralWrite));
+        }
+    }
+
+    public MoonTools.ECS.System System { get; }
+    public string Name { get; }
+    public SystemSchedulePhase Phase { get; }
+    public string[] DependsOn { get; }
+    public int RegistrationIndex { get; }
+    public SystemAccessDeclaration Access { get; }
+}

Nerfed.Runtime/Scheduling/SystemSchedulePhase.cs

@@ -0,0 +1,9 @@
+namespace Nerfed.Runtime.Scheduling;
+
+public enum SystemSchedulePhase
+{
+    PreUpdate = 0,
+    Simulation = 1,
+    LateSimulation = 2,
+    PreRender = 3,
+}

Nerfed.Runtime/Scheduling/SystemScheduler.cs

@@ -0,0 +1,188 @@
+using MoonTools.ECS;
+
+namespace Nerfed.Runtime.Scheduling;
+
+public sealed class SystemScheduler
+{
+    private readonly List<SystemScheduleEntry> entries = new List<SystemScheduleEntry>();
+    private readonly SystemSchedulerOptions options;
+
+    public SystemScheduler(SystemSchedulerOptions options)
+    {
+        this.options = options ?? new SystemSchedulerOptions();
+    }
+
+    public IReadOnlyList<SystemScheduleEntry> Entries => entries;
+
+    public void Register(MoonTools.ECS.System system, SystemSchedulePhase phase, params string[] dependsOn)
+    {
+        ArgumentNullException.ThrowIfNull(system);
+        string[] dependencies = dependsOn?.Where(static value => !string.IsNullOrWhiteSpace(value)).ToArray() ?? Array.Empty<string>();
+        entries.Add(new SystemScheduleEntry(system, phase, dependencies, entries.Count));
+    }
+
+    public void Execute(TimeSpan delta)
+    {
+        if (entries.Count == 0)
+        {
+            return;
+        }
+
+        Dictionary<string, SystemScheduleEntry> byName = BuildNameIndex(entries);
+        ValidateDependencies(byName, entries);
+
+        foreach (SystemSchedulePhase phase in Enum.GetValues<SystemSchedulePhase>())
+        {
+            ExecutePhase(phase, delta, byName);
+        }
+    }
+
+    private static Dictionary<string, SystemScheduleEntry> BuildNameIndex(List<SystemScheduleEntry> allEntries)
+    {
+        var byName = new Dictionary<string, SystemScheduleEntry>(StringComparer.Ordinal);
+        foreach (SystemScheduleEntry entry in allEntries)
+        {
+            if (byName.ContainsKey(entry.Name))
+            {
+                throw new InvalidOperationException($"Duplicate scheduled system name '{entry.Name}'.");
+            }
+
+            byName.Add(entry.Name, entry);
+        }
+
+        return byName;
+    }
+
+    private void ValidateDependencies(Dictionary<string, SystemScheduleEntry> byName, List<SystemScheduleEntry> allEntries)
+    {
+        foreach (SystemScheduleEntry entry in allEntries)
+        {
+            foreach (string dependency in entry.DependsOn)
+            {
+                if (!byName.TryGetValue(dependency, out SystemScheduleEntry dependencyEntry))
+                {
+                    if (options.StrictDependencyValidation)
+                    {
+                        throw new InvalidOperationException($"Scheduled system '{entry.Name}' depends on missing system '{dependency}'.");
+                    }
+
+                    continue;
+                }
+
+                if (dependencyEntry.Phase > entry.Phase)
+                {
+                    throw new InvalidOperationException(
+                        $"Scheduled system '{entry.Name}' in phase {entry.Phase} cannot depend on later phase system '{dependency}' in phase {dependencyEntry.Phase}.");
+                }
+            }
+        }
+    }
+
+    private void ExecutePhase(SystemSchedulePhase phase, TimeSpan delta, Dictionary<string, SystemScheduleEntry> byName)
+    {
+        List<SystemScheduleEntry> phaseEntries = entries
+            .Where(entry => entry.Phase == phase)
+            .OrderBy(entry => entry.RegistrationIndex)
+            .ToList();
+
+        if (phaseEntries.Count == 0)
+        {
+            return;
+        }
+
+        var completed = new HashSet<string>(StringComparer.Ordinal);
+
+        while (completed.Count < phaseEntries.Count)
+        {
+            List<SystemScheduleEntry> ready = phaseEntries
+                .Where(entry => !completed.Contains(entry.Name) && DependenciesSatisfied(entry, completed, byName))
+                .OrderBy(entry => entry.RegistrationIndex)
+                .ToList();
+
+            if (ready.Count == 0)
+            {
+                throw new InvalidOperationException($"Cyclic or unsatisfied dependencies detected in phase {phase}.");
+            }
+
+            List<SystemScheduleEntry> batch = BuildNonConflictingBatch(ready);
+            ExecuteBatch(batch, delta, phase);
+
+            foreach (SystemScheduleEntry entry in batch)
+            {
+                completed.Add(entry.Name);
+            }
+        }
+    }
+
+    private static bool DependenciesSatisfied(SystemScheduleEntry entry, HashSet<string> completed, Dictionary<string, SystemScheduleEntry> byName)
+    {
+        foreach (string dependency in entry.DependsOn)
+        {
+            if (!byName.TryGetValue(dependency, out SystemScheduleEntry dependencyEntry))
+            {
+                continue;
+            }
+
+            if (dependencyEntry.Phase == entry.Phase && !completed.Contains(dependency))
+            {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    private static List<SystemScheduleEntry> BuildNonConflictingBatch(List<SystemScheduleEntry> ready)
+    {
+        var batch = new List<SystemScheduleEntry>(ready.Count);
+
+        for (int i = 0; i < ready.Count; i++)
+        {
+            SystemScheduleEntry candidate = ready[i];
+            bool conflicts = false;
+
+            for (int j = 0; j < batch.Count; j++)
+            {
+                if (candidate.Access.ConflictsWith(batch[j].Access))
+                {
+                    conflicts = true;
+                    break;
+                }
+            }
+
+            if (!conflicts)
+            {
+                batch.Add(candidate);
+            }
+        }
+
+        if (batch.Count == 0)
+        {
+            batch.Add(ready[0]);
+        }
+
+        return batch;
+    }
+
+    private void ExecuteBatch(List<SystemScheduleEntry> batch, TimeSpan delta, SystemSchedulePhase phase)
+    {
+        using ProfilerScope phaseScope = new($"Schedule.{phase}.Batch[{batch.Count}]");
+
+        if (options.EnableParallelSystemExecution && batch.Count > 1)
+        {
+            Parallel.ForEach(batch, entry => ExecuteSystem(entry, delta));
+            return;
+        }
+
+        for (int i = 0; i < batch.Count; i++)
+        {
+            ExecuteSystem(batch[i], delta);
+        }
+    }
+
+    private static void ExecuteSystem(SystemScheduleEntry entry, TimeSpan delta)
+    {
+        using ProfilerScope scope = new(entry.Name);
+        entry.System.Update(delta);
+    }
+}

Nerfed.Runtime/Scheduling/SystemSchedulerOptions.cs

@@ -0,0 +1,7 @@
+namespace Nerfed.Runtime.Scheduling;
+
+public sealed class SystemSchedulerOptions
+{
+    public bool EnableParallelSystemExecution { get; set; }
+    public bool StrictDependencyValidation { get; set; } = true;
+}

Nerfed.Runtime/Systems/Synthetic/DummyLongJobConsumerSystem.cs

@@ -0,0 +1,47 @@
+using MoonTools.ECS;
+using Nerfed.Runtime.Scheduling;
+
+namespace Nerfed.Runtime.Systems.Synthetic;
+
+public sealed class DummyLongJobConsumerSystem : MoonTools.ECS.System, IParallelSystemMetadata
+{
+    private readonly JobSystem jobs;
+    private readonly DummyLongJobSharedState state;
+    private readonly bool requireCompletion;
+
+    public DummyLongJobConsumerSystem(
+        World world,
+        DummyLongJobSharedState state,
+        JobSystem jobs,
+        bool requireCompletion) : base(world)
+    {
+        this.state = state;
+        this.jobs = jobs;
+        this.requireCompletion = requireCompletion;
+    }
+
+    public string ScheduleName => nameof(DummyLongJobConsumerSystem);
+
+    // Consumer/apply stage is where structural world work should happen in real systems.
+    public SystemAccessDeclaration AccessDeclaration => SystemAccessDeclaration.Empty;
+
+    public override void Update(TimeSpan delta)
+    {
+        JobHandle handle = state.InFlight;
+        if (!handle.IsValid)
+        {
+            return;
+        }
+
+        if (!requireCompletion && !jobs.IsCompleted(handle))
+        {
+            return;
+        }
+
+        jobs.Wait(handle);
+        jobs.TryForget(handle);
+
+        state.InFlight = default;
+        state.ConsumeCount++;
+    }
+}

Nerfed.Runtime/Systems/Synthetic/DummyLongJobProducerSystem.cs

@@ -0,0 +1,53 @@
+using MoonTools.ECS;
+using Nerfed.Runtime.Scheduling;
+
+namespace Nerfed.Runtime.Systems.Synthetic;
+
+public sealed class DummyLongJobProducerSystem : MoonTools.ECS.System, IParallelSystemMetadata
+{
+    private readonly JobSystem jobs;
+    private readonly DummyLongJobSharedState state;
+    private readonly TimeSpan duration;
+    private readonly DummyWorkloadMode mode;
+    private readonly JobDeadlineMode deadline;
+    private int seed;
+
+    public DummyLongJobProducerSystem(
+        World world,
+        DummyLongJobSharedState state,
+        JobSystem jobs,
+        TimeSpan duration,
+        DummyWorkloadMode mode,
+        JobDeadlineMode deadline,
+        int initialSeed = 1) : base(world)
+    {
+        this.state = state;
+        this.jobs = jobs;
+        this.duration = duration;
+        this.mode = mode;
+        this.deadline = deadline;
+        seed = initialSeed;
+    }
+
+    public string ScheduleName => nameof(DummyLongJobProducerSystem);
+
+    // Producer pattern: reads current world state and emits immutable job payload.
+    public SystemAccessDeclaration AccessDeclaration => SystemAccessDeclaration.Empty;
+
+    public override void Update(TimeSpan delta)
+    {
+        if (state.InFlight.IsValid)
+        {
+            return;
+        }
+
+        int capturedSeed = seed;
+        state.InFlight = jobs.Submit(
+            () => state.LastResult = DummyWorkloadRunner.Run(duration, mode, capturedSeed),
+            deadline,
+            nameof(DummyLongJobProducerSystem));
+
+        seed = unchecked(capturedSeed + 1);
+        state.SubmitCount++;
+    }
+}

Nerfed.Runtime/Systems/Synthetic/DummyLongJobSharedState.cs

@@ -0,0 +1,9 @@
+namespace Nerfed.Runtime.Systems.Synthetic;
+
+public sealed class DummyLongJobSharedState
+{
+    public JobHandle InFlight;
+    public int LastResult;
+    public int SubmitCount;
+    public int ConsumeCount;
+}

Nerfed.Runtime/Systems/Synthetic/DummyMainThreadWorkSystem.cs

@@ -0,0 +1,34 @@
+using MoonTools.ECS;
+using Nerfed.Runtime.Scheduling;
+
+namespace Nerfed.Runtime.Systems.Synthetic;
+
+public sealed class DummyMainThreadWorkSystem : MoonTools.ECS.System, IParallelSystemMetadata
+{
+    private readonly TimeSpan duration;
+    private readonly DummyWorkloadMode mode;
+    private readonly string scheduleName;
+    private int seed;
+
+    public DummyMainThreadWorkSystem(
+        World world,
+        TimeSpan duration,
+        DummyWorkloadMode mode,
+        string scheduleName,
+        int initialSeed = 1) : base(world)
+    {
+        this.duration = duration;
+        this.mode = mode;
+        this.scheduleName = scheduleName;
+        seed = initialSeed;
+    }
+
+    public string ScheduleName => scheduleName;
+
+    public SystemAccessDeclaration AccessDeclaration => SystemAccessDeclaration.Empty;
+
+    public override void Update(TimeSpan delta)
+    {
+        seed = DummyWorkloadRunner.Run(duration, mode, seed);
+    }
+}

Nerfed.Runtime/Systems/Synthetic/DummyWorkloadMode.cs

@@ -0,0 +1,8 @@
+namespace Nerfed.Runtime.Systems.Synthetic;
+
+public enum DummyWorkloadMode
+{
+    Spin,
+    Sleep,
+    Compute,
+}

Nerfed.Runtime/Systems/Synthetic/DummyWorkloadRunner.cs

@@ -0,0 +1,54 @@
+using System.Diagnostics;
+
+namespace Nerfed.Runtime.Systems.Synthetic;
+
+internal static class DummyWorkloadRunner
+{
+    public static int Run(TimeSpan duration, DummyWorkloadMode mode, int seed)
+    {
+        return mode switch
+        {
+            DummyWorkloadMode.Sleep => Sleep(duration, seed),
+            DummyWorkloadMode.Compute => Compute(duration, seed),
+            _ => Spin(duration, seed),
+        };
+    }
+
+    private static int Sleep(TimeSpan duration, int seed)
+    {
+        if (duration > TimeSpan.Zero)
+        {
+            Thread.Sleep(duration);
+        }
+
+        return seed;
+    }
+
+    private static int Spin(TimeSpan duration, int seed)
+    {
+        Stopwatch stopwatch = Stopwatch.StartNew();
+        int value = seed;
+        while (stopwatch.Elapsed < duration)
+        {
+            value = unchecked((value * 1664525) + 1013904223);
+            Thread.SpinWait(128);
+        }
+
+        return value;
+    }
+
+    private static int Compute(TimeSpan duration, int seed)
+    {
+        Stopwatch stopwatch = Stopwatch.StartNew();
+        int value = seed;
+        while (stopwatch.Elapsed < duration)
+        {
+            for (int i = 0; i < 2048; i++)
+            {
+                value = unchecked((value << 5) - value + i);
+            }
+        }
+
+        return value;
+    }
+}