[.NET] STAThread

在WindowForm应用程序中主要的线程，是采用一种称为「Single-Threaded Apartment(STA)」的线程模型。这个STA线程模型，在线程内加入了讯息帮浦等等机制，减少开发人员撰写窗口程序的工作量。相关的信息可以参考：[Object-oriented] 线程。

而在开发类别库的时候，如果要使用类似的STA线程模型，可以使用下列的程序代码提供的类别来完成。

namespace CLK.Threading
{
    public class STAThread
    {
        // Enum
        private enum ThreadState
        {
            Started,
            Stopping,
            Stopped,
        }


        // Fields
        private readonly object _syncRoot = new object();

        private readonly BlockingQueue<Action> _actionQueue = null;

        private Thread _thread = null;

        private ManualResetEvent _threadEvent = null;

        private ThreadState _threadState = ThreadState.Stopped;       


        // Constructor
        public STAThread()
        {
            // ActionQueue
            _actionQueue = new BlockingQueue<Action>();
                        
            // ThreadEvent
            _threadEvent = new ManualResetEvent(true);

            // ThreadState
            _threadState = ThreadState.Stopped;       
        }


        // Methods
        public void Start()
        {            
            // Sync
            lock (_syncRoot)
            {
                // ThreadState
                if (_threadState != ThreadState.Stopped) throw new InvalidOperationException();
                _threadState = ThreadState.Started;
            }

            // Thread
            _thread = new Thread(this.Operate);
            _thread.Name = string.Format("Class:{0}, Id:{1}", "STAThread", _thread.ManagedThreadId);
            _thread.IsBackground = false;
            _thread.Start();
        }

        public void Stop()
        {
            // Sync
            lock (_syncRoot)
            {
                // ThreadState
                if (_threadState != ThreadState.Started) throw new InvalidOperationException();
                _threadState = ThreadState.Stopping;

                // ActionQueue
                _actionQueue.Release();
            }

            // Wait
            _threadEvent.WaitOne();
        }


        public void Post(SendOrPostCallback callback, object state)
        {
            #region Contracts

            if (callback == null) throw new ArgumentNullException();

            #endregion
            
            // Action
            Action action = delegate()
            {
                try
                {
                    callback(state);
                }
                catch (Exception ex)
                {
                    Debug.Fail(string.Format("Delegate:{0}, State:{1}, Message:{2}", callback.GetType(), "Exception", ex.Message));
                }
            };

            // Sync
            lock (_syncRoot)
            {
                // ThreadState
                if (_threadState != ThreadState.Started) throw new InvalidOperationException();

                // ActionQueue
                _actionQueue.Enqueue(action);
            }                       
        }

        public void Send(SendOrPostCallback callback, object state)
        {
            #region Contracts

            if (callback == null) throw new ArgumentNullException();

            #endregion

            // Action 
            ManualResetEvent actionEvent = new ManualResetEvent(false);
            Action action = delegate()
            {
                try
                {
                    callback(state);
                }
                catch (Exception ex)
                {
                    Debug.Fail(string.Format("Delegate:{0}, State:{1}, Message:{2}", callback.GetType(), "Exception", ex.Message));
                }
                finally
                {
                    actionEvent.Set();
                }
            };

            // Sync
            lock (_syncRoot)
            {
                // ThreadState
                if (_threadState != ThreadState.Started) throw new InvalidOperationException();

                // ActionQueue
                if (Thread.CurrentThread != _thread)
                {
                    _actionQueue.Enqueue(action);
                }
            }

            // Execute
            if (Thread.CurrentThread == _thread)
            {
                action();
            }

            // Wait
            actionEvent.WaitOne();
        }


        private void Operate()
        {
            try
            {
                // Begin
                _threadEvent.Reset();

                // Operate
                while (true)
                {
                    // Action
                    Action action = _actionQueue.Dequeue();

                    // Execute
                    if (action != null)
                    {
                        action();
                    }
                                        
                    // ThreadState
                    if (action == null)
                    {
                        lock (_syncRoot)
                        {
                            if (_threadState == ThreadState.Stopping)
                            {
                                return;
                            }
                        }
                    }
                }
            }
            finally
            {
                // End
                lock (_syncRoot)
                {
                    _threadState = ThreadState.Stopped;
                }
                _threadEvent.Set();
            }
        }
    }
}

namespace CLK.Threading
{
    public class BlockingQueue<T>
    {
        // Fields        
        private readonly object _syncRoot = new object();

        private readonly WaitHandle[] _waitHandles = null;

        private readonly Queue<T> _itemQueue = null;

        private readonly Semaphore _itemQueueSemaphore = null;

        private readonly ManualResetEvent _itemQueueReleaseEvent = null;


        // Constructors
        public BlockingQueue()
        {
            // Default 
            _itemQueue = new Queue<T>();
            _itemQueueSemaphore = new Semaphore(0, int.MaxValue);
            _itemQueueReleaseEvent = new ManualResetEvent(false);
            _waitHandles = new WaitHandle[] { _itemQueueSemaphore, _itemQueueReleaseEvent };
        }


        // Methods
        public void Enqueue(T item)
        {
            lock (_syncRoot)
            {
                _itemQueue.Enqueue(item);
                _itemQueueSemaphore.Release();
            }
        }

        public T Dequeue()
        {
            WaitHandle.WaitAny(_waitHandles);
            lock (_syncRoot)
            {
                if (_itemQueue.Count > 0)
                {
                    return _itemQueue.Dequeue();
                }
            }
            return default(T);
        }

        public void Release()
        {
            lock (_syncRoot)
            {
                _itemQueueReleaseEvent.Set();
            }
        }

        public void Reset()
        {
            lock (_syncRoot)
            {
                _itemQueue.Clear();
                _itemQueueSemaphore.Close();
                _itemQueueReleaseEvent.Reset();
            }
        }
    }
}