ScadaBridge/lmxproxy/src/ZB.MOM.WW.LmxProxy.Host/MxAccess/StaDispatchThread.cs

using System;
using System.Collections.Concurrent;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;
using Serilog;

namespace ZB.MOM.WW.LmxProxy.Host.MxAccess
{
    /// <summary>
    ///     Dedicated STA thread with a message pump for COM interop.
    ///     All COM operations are dispatched to this thread via a BlockingCollection.
    /// </summary>
    public sealed class StaDispatchThread : IDisposable
    {
        private static readonly ILogger Log = Serilog.Log.ForContext<StaDispatchThread>();

        private readonly BlockingCollection<Action> _workQueue = new BlockingCollection<Action>();
        private readonly Thread _staThread;
        private volatile bool _disposed;

        public StaDispatchThread(string threadName = "MxAccess-STA")
        {
            _staThread = new Thread(StaThreadLoop)
            {
                Name = threadName,
                IsBackground = true
            };
            _staThread.SetApartmentState(ApartmentState.STA);
            _staThread.Start();
            Log.Information("STA dispatch thread '{ThreadName}' started", threadName);
        }

        /// <summary>
        ///     Dispatches an action to the STA thread and returns a Task that completes
        ///     when the action finishes.
        /// </summary>
        public Task DispatchAsync(Action action)
        {
            if (_disposed) throw new ObjectDisposedException(nameof(StaDispatchThread));

            var tcs = new TaskCompletionSource<bool>(TaskCreationOptions.RunContinuationsAsynchronously);
            _workQueue.Add(() =>
            {
                try
                {
                    action();
                    tcs.TrySetResult(true);
                }
                catch (Exception ex)
                {
                    tcs.TrySetException(ex);
                }
            });
            return tcs.Task;
        }

        /// <summary>
        ///     Dispatches a function to the STA thread and returns its result.
        /// </summary>
        public Task<T> DispatchAsync<T>(Func<T> func)
        {
            if (_disposed) throw new ObjectDisposedException(nameof(StaDispatchThread));

            var tcs = new TaskCompletionSource<T>(TaskCreationOptions.RunContinuationsAsynchronously);
            _workQueue.Add(() =>
            {
                try
                {
                    var result = func();
                    tcs.TrySetResult(result);
                }
                catch (Exception ex)
                {
                    tcs.TrySetException(ex);
                }
            });
            return tcs.Task;
        }

        private void StaThreadLoop()
        {
            Log.Debug("STA thread loop started");

            // Process the work queue. GetConsumingEnumerable blocks until
            // items are available or the collection is marked complete.
            foreach (var action in _workQueue.GetConsumingEnumerable())
            {
                try
                {
                    action();
                }
                catch (Exception ex)
                {
                    // Should not happen — actions set TCS exceptions internally.
                    Log.Error(ex, "Unhandled exception on STA thread");
                }

                // Pump COM messages between work items
                Application.DoEvents();
            }

            Log.Debug("STA thread loop exited");
        }

        public void Dispose()
        {
            if (_disposed) return;
            _disposed = true;

            _workQueue.CompleteAdding();

            // Wait for the STA thread to drain and exit
            if (_staThread.IsAlive && !_staThread.Join(TimeSpan.FromSeconds(10)))
            {
                Log.Warning("STA thread did not exit within 10 seconds");
            }

            _workQueue.Dispose();
            Log.Information("STA dispatch thread disposed");
        }
    }
}