Implement scheduling system with parallel execution support and dummy job systems

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);
+    }
+}