acdream/src/AcDream.App/Streaming/LandblockStreamer.cs

using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Channels;
using System.Threading.Tasks;
using AcDream.Core.World;

namespace AcDream.App.Streaming;

/// <summary>
/// Services landblock load/unload requests by invoking caller-supplied
/// factory delegates (the production instance wraps
/// <see cref="LandblockLoader.Load"/> for loading and
/// <see cref="AcDream.Core.Terrain.LandblockMesh.Build"/> for the terrain
/// mesh) and posting results to an outbox the render thread drains once
/// per OnUpdate.
///
/// <para>
/// <b>Thread model (#418):</b> <see cref="Start"/> spawns a small pool of
/// dedicated background worker threads (default
/// <see cref="DefaultWorkerCount"/>; the single-worker degenerate case is
/// the pre-#418 Phase A.5 T11+ shape). Jobs are striped across per-worker
/// lanes by landblock id, so every job for one landblock id executes on
/// one lane in enqueue order — a Load and Unload for the same id can never
/// race on two workers. <see cref="EnqueueLoad"/> and
/// <see cref="EnqueueUnload"/> write non-blocking to the owning lane's
/// inbox <see cref="Channel{T}"/>; each worker drains its lane and posts
/// <see cref="LandblockStreamResult"/> records to the shared outbox.
/// </para>
///
/// <para>
/// <b>DatCollection thread safety</b> is provided by the caller:
/// GameWindow's <c>_datLock</c> (Phase A.5 T10) serialises all
/// <c>DatCollection.Get&lt;T&gt;</c> calls. Both factory closures passed at
/// construction acquire that lock before reading dats. The workers never
/// touch <c>DatCollection</c> directly — they only call the factories.
/// </para>
///
/// <para>
/// Unloads pass through the outbox as <see cref="LandblockStreamResult.Unloaded"/>
/// records so the render thread can release GPU state on the next drain —
/// the streamer never touches GPU resources directly.
/// </para>
///
/// <remarks>
/// Threading: <see cref="DrainCompletions"/> must be called from a single
/// consumer thread (the render thread in production). All other public
/// methods are thread-safe. Completion arrival order is preserved per
/// landblock id (per lane); across different landblocks it is arbitrary,
/// which the single consumer already tolerates — the StreamingController's
/// admission classifies each result independently into per-priority FIFOs.
/// </remarks>
/// </summary>
public sealed class LandblockStreamer : IDisposable, ILandblockCompletionSource
{
    /// <summary>
    /// Default drain batch size. Tuned to cap GPU upload work the render
    /// thread does per frame while still draining a moderate backlog in a
    /// few frames. Callers can override on a per-call basis.
    /// </summary>
    public const int DefaultDrainBatchSize = 4;

    /// <summary>
    /// Default build worker pool size: leave two cores for the render and
    /// update threads, cap at 8 (the login window's ~625 builds saturate
    /// well before that), floor 1 (the pre-#418 single-worker shape).
    /// </summary>
    public static int DefaultWorkerCount =>
        Math.Max(1, Math.Min(Environment.ProcessorCount - 2, 8));

    private readonly Func<LandblockBuildRequest, LandblockBuild?> _loadLandblock;
    private readonly bool _supportsRequestOrigin;
    private readonly Func<uint, LoadedLandblock?, AcDream.Core.Terrain.LandblockMeshData?> _buildMeshOrNull;
    private readonly Channel<LandblockStreamJob>[] _lanes;
    private readonly Channel<LandblockStreamResult> _outbox;
    private readonly CancellationTokenSource _cancel = new();
    private readonly object _inboxGate = new();
    private Thread[]? _workers;
    private int _activeWorkers;
    private Exception? _workerFailure;
    private int _completionBacklog;
    private int _disposed;
    private readonly object _disposeGate = new();
    private bool _disposeCompleted;

    /// <summary>
    /// Primary constructor. The factory receives the complete immutable
    /// request, including job kind and enqueue-time world origin. ISSUE #54
    /// uses the kind to skip entity hydration for heightmap-only far loads.
    /// </summary>
    private LandblockStreamer(
        Func<LandblockBuildRequest, LandblockBuild?> loadLandblock,
        Func<uint, LoadedLandblock?, AcDream.Core.Terrain.LandblockMeshData?>? buildMeshOrNull,
        bool supportsRequestOrigin,
        int? workerCount)
    {
        if (workerCount is < 1)
        {
            throw new ArgumentOutOfRangeException(
                nameof(workerCount),
                workerCount,
                "The landblock build pool needs at least one worker.");
        }
        _loadLandblock = loadLandblock;
        _supportsRequestOrigin = supportsRequestOrigin;
        // Default: no mesh build (returns null → Failed result). Production
        // wires in LandblockMesh.Build via the T12 construction site.
        _buildMeshOrNull = buildMeshOrNull ?? ((_, _) => null);
        int lanes = workerCount ?? DefaultWorkerCount;
        _lanes = new Channel<LandblockStreamJob>[lanes];
        for (int i = 0; i < lanes; i++)
        {
            _lanes[i] = Channel.CreateUnbounded<LandblockStreamJob>(
                new UnboundedChannelOptions { SingleReader = true, SingleWriter = false });
        }
        // SingleWriter = false: every pool worker posts completions.
        _outbox = Channel.CreateUnbounded<LandblockStreamResult>(
            new UnboundedChannelOptions { SingleReader = true, SingleWriter = false });
    }

    /// <summary>
    /// Creates the request-aware production streamer. A named factory keeps
    /// legacy one-parameter loader lambdas source-compatible without an
    /// ambiguous constructor overload.
    /// </summary>
    public static LandblockStreamer CreateForRequests(
        Func<LandblockBuildRequest, LandblockBuild?> loadLandblock,
        Func<uint, LoadedLandblock?, AcDream.Core.Terrain.LandblockMeshData?>? buildMeshOrNull = null,
        int? workerCount = null) =>
        new(loadLandblock, buildMeshOrNull, supportsRequestOrigin: true, workerCount);

    /// <summary>
    /// Compatibility constructor for build factories that predate the
    /// immutable request/origin seam.
    /// </summary>
    public LandblockStreamer(
        Func<uint, LandblockStreamJobKind, LandblockBuild?> loadLandblock,
        Func<uint, LoadedLandblock?, AcDream.Core.Terrain.LandblockMeshData?>? buildMeshOrNull = null,
        int? workerCount = null)
        : this(
            request => loadLandblock(request.LandblockId, request.Kind) is { } build
                ? build
                : null,
            buildMeshOrNull,
            supportsRequestOrigin: false,
            workerCount)
    {
    }

    /// <summary>
    /// Compatibility constructor for loaders that have no App-owned cell payload.
    /// Production uses the <see cref="LandblockBuild"/> overload so render state
    /// remains attached to the exact streaming completion that produced it.
    /// </summary>
    public LandblockStreamer(
        Func<uint, LandblockStreamJobKind, LoadedLandblock?> loadLandblock,
        Func<uint, LoadedLandblock?, AcDream.Core.Terrain.LandblockMeshData?>? buildMeshOrNull = null,
        int? workerCount = null)
        : this(
            request => loadLandblock(request.LandblockId, request.Kind) is { } landblock
                ? new LandblockBuild(landblock, Origin: request.Origin)
                : null,
            buildMeshOrNull,
            supportsRequestOrigin: false,
            workerCount)
    {
    }

    /// <summary>
    /// Back-compat overload — wraps a kind-agnostic factory so existing test code
    /// that doesn't care about the JobKind branch keeps compiling. The wrapper
    /// ignores the kind and calls the factory once per LB regardless of tier.
    /// New production code should use <see cref="CreateForRequests"/>.
    /// </summary>
    public LandblockStreamer(
        Func<uint, LoadedLandblock?> loadLandblock,
        Func<uint, LoadedLandblock?, AcDream.Core.Terrain.LandblockMeshData?>? buildMeshOrNull = null,
        int? workerCount = null)
        : this(
            request => loadLandblock(request.LandblockId) is { } landblock
                ? new LandblockBuild(landblock, Origin: request.Origin)
                : null,
            buildMeshOrNull,
            supportsRequestOrigin: false,
            workerCount)
    {
    }

    /// <summary>Configured pool size (also the lane count).</summary>
    internal int WorkerCount => _lanes.Length;

    /// <summary>
    /// Lane (worker) that owns every job for <paramref name="landblockId"/>.
    /// Landblock ids carry their identity in the high 16 bits (0xXXYYFFFF —
    /// the low word is constant across ids), so the id is mixed with a
    /// Knuth multiplicative hash before reduction; a bare modulo would map
    /// every id to one lane. Internal so tests can construct deterministic
    /// per-lane contention.
    /// </summary>
    internal int LaneFor(uint landblockId)
    {
        if (_lanes.Length == 1)
            return 0;
        uint mixed = (landblockId >> 16) * 2654435761u;
        return (int)(mixed % (uint)_lanes.Length);
    }

    /// <summary>
    /// Activate the dedicated background worker threads. Idempotent and
    /// thread-safe: concurrent callers will only spawn one pool; subsequent
    /// calls are no-ops. Serialized with disposal so a worker can never start
    /// after the owning DAT lifetime has been released.
    /// </summary>
    public void Start()
    {
        lock (_disposeGate)
        {
            if (System.Threading.Volatile.Read(ref _disposed) != 0)
                throw new ObjectDisposedException(nameof(LandblockStreamer));
            if (_workers is not null)
                return;

            var workers = new Thread[_lanes.Length];
            // Armed before any worker can run so the last worker to exit —
            // however fast — is the one that completes the outbox.
            System.Threading.Volatile.Write(ref _activeWorkers, workers.Length);
            for (int i = 0; i < workers.Length; i++)
            {
                int lane = i;
                workers[i] = new Thread(() => WorkerLoop(lane))
                {
                    IsBackground = true,
                    Name = workers.Length == 1
                        ? "acdream.streaming.worker"
                        : $"acdream.streaming.worker.{lane}",
                };
            }
            foreach (Thread worker in workers)
                worker.Start();
            _workers = workers;
        }
    }

    /// <summary>
    /// Non-blocking enqueue. The worker drains the inbox and posts a
    /// <see cref="LandblockStreamResult.Loaded"/> (or
    /// <see cref="LandblockStreamResult.Failed"/>) to the outbox.
    /// </summary>
    public void EnqueueLoad(
        uint landblockId,
        LandblockStreamJobKind kind = LandblockStreamJobKind.LoadNear,
        ulong generation = 0)
    {
        if (_supportsRequestOrigin)
        {
            throw new InvalidOperationException(
                "Request-aware landblock loaders require an explicit captured origin.");
        }
        EnqueueLoad(new LandblockBuildRequest(
            landblockId,
            kind,
            generation,
            default));
    }

    /// <summary>
    /// Non-blocking enqueue of the exact request captured by the update
    /// thread. The worker and completion retain its origin unchanged.
    /// </summary>
    public void EnqueueLoad(LandblockBuildRequest request)
    {
        if (System.Threading.Volatile.Read(ref _disposed) != 0)
            throw new ObjectDisposedException(nameof(LandblockStreamer));
        if (_supportsRequestOrigin && !request.Origin.IsSpecified)
        {
            throw new InvalidOperationException(
                "Request-aware landblock loaders require a specified captured origin.");
        }
        if (!_supportsRequestOrigin && request.Origin.IsSpecified)
        {
            throw new InvalidOperationException(
                "This compatibility landblock loader cannot consume a non-default build origin. " +
                "Use LandblockStreamer.CreateForRequests.");
        }
        AcDream.Core.Physics.PhysicsDiagnostics.LogTeleport(
            "ENQ",
            request.LandblockId,
            $"kind={request.Kind} origin=({request.Origin.CenterX:X2},{request.Origin.CenterY:X2})");
        WriteJob(new LandblockStreamJob.Load(
            request.LandblockId,
            request.Kind,
            request.Generation,
            request.Origin));
    }

    /// <summary>
    /// Non-blocking enqueue. The worker posts a
    /// <see cref="LandblockStreamResult.Unloaded"/> to the outbox.
    /// </summary>
    public void EnqueueUnload(uint landblockId, ulong generation = 0)
    {
        WriteJob(new LandblockStreamJob.Unload(landblockId, generation));
    }

    /// <summary>
    /// Cancel every queued-but-not-started Load. Posts a
    /// <see cref="LandblockStreamJob.ClearLoads"/> control job to EVERY lane
    /// (one atomic broadcast under the enqueue gate, so a load enqueued
    /// before this call is ordered ahead of its lane's ClearLoads copy and
    /// dropped) which each worker honours at read time, dropping all pending
    /// Loads from both of its priority queues (Unloads survive). Used on the
    /// dungeon-entry edge to abort the in-flight 25×25 neighbor window so the
    /// ~129 ocean-grid dungeons never finish loading (#133 FPS). Loads a
    /// worker has ALREADY dequeued still complete (up to one per worker);
    /// the StreamingController's collapsed-sweep unloads those few.
    /// </summary>
    public void ClearPendingLoads()
    {
        WriteJob(new LandblockStreamJob.ClearLoads());
    }

    private void WriteJob(LandblockStreamJob job)
    {
        // Serialize the writers' terminal transition with enqueue. Without
        // this small lifecycle gate a worker crash could complete a lane
        // between the caller's state check and TryWrite, silently dropping a
        // landblock request. The same gate makes the ClearLoads broadcast
        // atomic with respect to concurrent enqueues. Enqueues are
        // destination-boundary events, not a per-frame hot path.
        lock (_inboxGate)
        {
            if (System.Threading.Volatile.Read(ref _disposed) != 0)
                throw new ObjectDisposedException(nameof(LandblockStreamer));
            if (_workerFailure is { } failure)
                throw new InvalidOperationException("A landblock streaming worker has terminated.", failure);
            if (job is LandblockStreamJob.ClearLoads)
            {
                foreach (Channel<LandblockStreamJob> lane in _lanes)
                {
                    if (!lane.Writer.TryWrite(job))
                        throw new InvalidOperationException("The landblock streaming inbox is no longer accepting work.");
                }
                return;
            }
            if (!_lanes[LaneFor(job.LandblockId)].Writer.TryWrite(job))
                throw new InvalidOperationException("The landblock streaming inbox is no longer accepting work.");
        }
    }

    /// <summary>
    /// Drain up to <paramref name="maxBatchSize"/> completed results.
    /// Non-blocking. Call from the render thread once per OnUpdate.
    /// </summary>
    /// <remarks>
    /// Must be called from a single consumer thread. The outbox channel is
    /// configured with SingleReader = true and will throw on concurrent reads.
    /// </remarks>
    public IReadOnlyList<LandblockStreamResult> DrainCompletions(int maxBatchSize = DefaultDrainBatchSize)
    {
        var batch = new List<LandblockStreamResult>(maxBatchSize);
        while (batch.Count < maxBatchSize && TryRead(out var result))
        {
            if (result is null)
                throw new InvalidOperationException(
                    "The completion channel returned a null result.");
            batch.Add(result);
        }
        return batch;
    }

    public int BacklogCount => Math.Max(
        0,
        System.Threading.Volatile.Read(ref _completionBacklog));

    public bool TryPeek(out LandblockStreamResult? result) =>
        _outbox.Reader.TryPeek(out result);

    public bool TryRead(out LandblockStreamResult? result)
    {
        if (!_outbox.Reader.TryRead(out result))
            return false;
        System.Threading.Interlocked.Decrement(ref _completionBacklog);
        return true;
    }

    private void PublishResult(LandblockStreamResult result)
    {
        if (_outbox.Writer.TryWrite(result))
            System.Threading.Interlocked.Increment(ref _completionBacklog);
    }

    private void WorkerLoop(int laneIndex)
    {
        ChannelReader<LandblockStreamJob> inbox = _lanes[laneIndex].Reader;
        var highPriority = new Queue<LandblockStreamJob>();
        var lowPriority = new Queue<LandblockStreamJob>();

        try
        {
            // Safe to block: this is a dedicated worker thread with no
            // SynchronizationContext, so .Result/.GetResult cannot deadlock
            // against any captured continuation. Using the sync pattern
            // here keeps the loop linear; an async-enumerable alternative
            // would force WorkerLoop to be async Task and lose the
            // simple thread-start shape.
            while (!_cancel.Token.IsCancellationRequested)
            {
                if (highPriority.Count == 0 &&
                    lowPriority.Count == 0 &&
                    !inbox.WaitToReadAsync(_cancel.Token).AsTask().GetAwaiter().GetResult())
                {
                    break;
                }

                while (inbox.TryRead(out var job))
                {
                    if (job is LandblockStreamJob.ClearLoads)
                    {
                        // Dungeon-entry cancellation: drop every queued Load,
                        // keep Unloads. Handled at read time so it supersedes
                        // Loads sitting in the priority queues ahead of it.
                        DropLoadJobs(highPriority);
                        DropLoadJobs(lowPriority);
                        continue;
                    }
                    EnqueuePrioritized(job, highPriority, lowPriority);
                }

                if (highPriority.Count == 0 && lowPriority.Count == 0)
                    continue;

                if (_cancel.Token.IsCancellationRequested) return;
                var next = highPriority.Count > 0
                    ? highPriority.Dequeue()
                    : lowPriority.Dequeue();
                HandleJob(next);
            }
        }
        catch (OperationCanceledException) { /* graceful shutdown */ }
        catch (Exception ex)
        {
            // Last-ditch: surface via outbox so the caller at least sees
            // something. We never retry a crashed worker; any worker crash
            // terminates the pool (matching the single-worker contract that
            // a crash ends all job processing). A sibling that merely
            // observed the crashed worker's lane completion (the wrapped
            // ChannelClosedException) exits quietly instead of reporting a
            // second, spurious crash.
            bool cascade;
            lock (_inboxGate)
            {
                cascade = _workerFailure is not null && ex is ChannelClosedException;
                _workerFailure ??= ex;
                foreach (Channel<LandblockStreamJob> lane in _lanes)
                    lane.Writer.TryComplete(ex);
            }
            if (!cascade)
            {
                PublishResult(new LandblockStreamResult.WorkerCrashed(
                    _lanes.Length == 1
                        ? ex.ToString()
                        : $"worker {laneIndex}: {ex}"));
                // Stop the sibling workers. Safe against Dispose: its
                // CTS disposal only happens after every worker (this one
                // included) has been joined.
                _cancel.Cancel();
            }
        }
        finally
        {
            // The outbox has N writers; only the last worker out may
            // complete it, or a crashed worker would silently drop the
            // still-running workers' completions.
            if (Interlocked.Decrement(ref _activeWorkers) == 0)
                _outbox.Writer.TryComplete();
        }
    }

    private static void EnqueuePrioritized(
        LandblockStreamJob job,
        Queue<LandblockStreamJob> highPriority,
        Queue<LandblockStreamJob> lowPriority)
    {
        if (job is LandblockStreamJob.Load
            {
                Kind: LandblockStreamJobKind.LoadNear or LandblockStreamJobKind.PromoteToNear
            } high)
        {
            // Near-tier jobs are visible-content critical. They supersede an
            // older queued LoadFar for the same landblock: LoadNear obviously
            // loads everything, and PromoteToNear now carries mesh data so the
            // render thread can run the full near-tier apply side effects. If a
            // LoadFar is already being processed, the owning lane's worker
            // naturally finishes it before the promotion is dequeued (every
            // job for one landblock id lives on one lane).
            RemoveLowPriorityJobsForLandblock(
                lowPriority,
                high.LandblockId,
                removeLoadFar: true,
                removeUnload: true);
            highPriority.Enqueue(job);
            return;
        }

        lowPriority.Enqueue(job);
    }

    /// <summary>
    /// Drop every <see cref="LandblockStreamJob.Load"/> from a priority queue,
    /// preserving Unloads (and any other control jobs). Rotates the queue once
    /// in place. Used by the <see cref="LandblockStreamJob.ClearLoads"/> path.
    /// </summary>
    private static void DropLoadJobs(Queue<LandblockStreamJob> queue)
    {
        int count = queue.Count;
        for (int i = 0; i < count; i++)
        {
            var job = queue.Dequeue();
            if (job is not LandblockStreamJob.Load)
                queue.Enqueue(job);
        }
    }

    private static void RemoveLowPriorityJobsForLandblock(
        Queue<LandblockStreamJob> queue,
        uint landblockId,
        bool removeLoadFar,
        bool removeUnload)
    {
        int count = queue.Count;
        for (int i = 0; i < count; i++)
        {
            var job = queue.Dequeue();
            bool remove = job.LandblockId == landblockId && job switch
            {
                LandblockStreamJob.Load { Kind: LandblockStreamJobKind.LoadFar } => removeLoadFar,
                LandblockStreamJob.Unload => removeUnload,
                _ => false
            };
            if (!remove)
                queue.Enqueue(job);
        }
    }

    private void HandleJob(LandblockStreamJob job)
    {
        switch (job)
        {
            case LandblockStreamJob.Load load:
                // ISSUE #54 (post-A.5): JobKind is now plumbed through to the
                // factory, so far-tier loads can skip LandBlockInfo + scenery
                // + interior hydration on the worker thread (heightmap-only).
                // The post-load entity-strip below is retained as a Debug
                // assertion + Release safety net for the case where a buggy
                // factory returns far-tier with entities anyway.
                try
                {
                    var build = _loadLandblock(load.Request);
                    if (build is null)
                    {
                        PublishResult(new LandblockStreamResult.Failed(
                            load.LandblockId, "LandblockLoader.Load returned null", load.Generation));
                        break;
                    }
                    if (build.Origin != load.Origin)
                    {
                        PublishResult(new LandblockStreamResult.Failed(
                            load.LandblockId,
                            $"Landblock build origin {build.Origin} did not match request origin {load.Origin}",
                            load.Generation));
                        break;
                    }
                    var lb = build.Landblock;
                    if (load.Kind == LandblockStreamJobKind.PromoteToNear)
                    {
                        var promotedMesh = _buildMeshOrNull(load.LandblockId, lb);
                        if (promotedMesh is null)
                        {
                            PublishResult(new LandblockStreamResult.Failed(
                                load.LandblockId, "buildMeshOrNull returned null", load.Generation));
                            break;
                        }
                        PublishResult(new LandblockStreamResult.Promoted(
                            load.LandblockId, build, promotedMesh, load.Generation));
                        break;
                    }
                    var mesh = _buildMeshOrNull(load.LandblockId, lb);
                    if (mesh is null)
                    {
                        PublishResult(new LandblockStreamResult.Failed(
                            load.LandblockId, "buildMeshOrNull returned null", load.Generation));
                        break;
                    }
                    var tier = load.Kind == LandblockStreamJobKind.LoadFar
                        ? LandblockStreamTier.Far : LandblockStreamTier.Near;
                    if (tier == LandblockStreamTier.Far)
                    {
                        // Belt-and-suspenders: factory should have skipped
                        // entity hydration for LoadFar. If it didn't, fail
                        // loud in Debug builds and strip in Release.
                        bool hasNearPayload =
                            lb.Entities.Count > 0 ||
                            build.EnvCells is not null ||
                            lb.PhysicsDats is { } physicsDats &&
                            (physicsDats.Info is not null ||
                             physicsDats.EnvCells.Count > 0 ||
                             physicsDats.Environments.Count > 0 ||
                             physicsDats.Setups.Count > 0 ||
                             physicsDats.GfxObjs.Count > 0);
                        System.Diagnostics.Debug.Assert(
                            !hasNearPayload,
                            $"Far-tier factory returned Near payload for LB 0x{load.LandblockId:X8}");
                        lb = new LoadedLandblock(
                            lb.LandblockId,
                            lb.Heightmap,
                            System.Array.Empty<AcDream.Core.World.WorldEntity>(),
                            PhysicsDatBundle.Empty);
                        build = new LandblockBuild(lb, Origin: build.Origin);
                    }
                    PublishResult(new LandblockStreamResult.Loaded(
                        load.LandblockId, tier, build, mesh, load.Generation));
                }
                catch (Exception ex)
                {
                    PublishResult(new LandblockStreamResult.Failed(
                        load.LandblockId, ex.ToString(), load.Generation));
                }
                break;

            case LandblockStreamJob.Unload unload:
                PublishResult(new LandblockStreamResult.Unloaded(
                    unload.LandblockId,
                    unload.Generation));
                break;
        }
    }

    public void Dispose()
    {
        lock (_disposeGate)
        {
            if (_disposeCompleted)
                return;

            System.Threading.Interlocked.Exchange(ref _disposed, 1);
            _cancel.Cancel();
            lock (_inboxGate)
            {
                foreach (Channel<LandblockStreamJob> lane in _lanes)
                    lane.Writer.TryComplete();
            }
            // The owner releases the memory-mapped DAT immediately after this
            // object. Join every actual worker without a grace-period timeout
            // so no native read can survive into that teardown.
            if (_workers is { } workers)
            {
                foreach (Thread worker in workers)
                    worker.Join();
            }
            _cancel.Dispose();
            _disposeCompleted = true;
        }
    }
}