Excel的线程 与 SynchronizationContext的实现

COM组件的线程模型与Excel多线程的背景知识

COM组件的线程模型被称之为Apartment模型，COM对象初始化时其执行上下文(Execution Context)，他要么和单个线程关联STA(Single Thread Apartment ) 要么和多个线程关联MTA(Multi Thread Apartment)。Excel是一种STA线程的应用程序，使用多线程直接怼会出问题，必须借助线程的同步上下文实现线程间的消息传递。

1、Excel 开发中与线程相关的若干问题参考这个链接：

https://www.cnblogs.com/yangecnu/p/Some-Thread-Releated-Problems-and-Solutions-in-Excel-Development.html

2、SynchronizationContext的实现参考这个链接（共3篇文章，进入链接后可以找到下一章的链接）：

https://www.codeproject.com/Articles/31971/Understanding-SynchronizationContext-Part-I

3、ExcelDNA是什么

Excel-DNA is an independent project to integrate .NET into Excel. With Excel-DNA you can make native (.xll) add-ins for Excel using C#, Visual Basic.NET or F#, providing high-performance user-defined functions (UDFs), custom ribbon interfaces and more. Your entire add-in can be packed into a single .xll file requiring no installation or registration.

https://excel-dna.net/

4、ExcelDNA下实现一个自定义的SynchronizationContext

https://groups.google.com/forum/#!searchin/exceldna/synchronizationcontext%7Csort:date/exceldna/pyybn0lSP8k/3DW6NOekCgAJ

ExcelDNA中的解决方案

  dynamic app;
         dynamic worksheet;

         public void Test(IRibbonControl ribbonControl)
         {
             app = ExcelDnaUtil.Application;
             worksheet = app.ActiveSheet;
             worksheet.Cells[, ].Value = Thread.CurrentThread.ManagedThreadId;
             Action<object> action = Run;
             Task task = new Task(action,ExcelSynchronizationContext.Current);
             task.Start();

         }
         private void Run(object context)
         {
             worksheet.Cells[, ].Value = Thread.CurrentThread.ManagedThreadId;

             for (int i = ; i < ; i++)
             {
                 Thread.Sleep();
                 ExcelAsyncUtil.QueueAsMacro(UpdateUI, i);
             }
         }

         private void UpdateUI(object state)
         {
             int i = (int)state + ;
             worksheet.Cells[i, ].Value = i;
             worksheet.Cells[i, ].Value = Thread.CurrentThread.ManagedThreadId;
         }

 Task task = new Task(action,ExcelSynchronizationContext.Current);

ExcelSynchronizationContext.Current为主线程的SynchronizationContext。

 ExcelAsyncUtil.QueueAsMacro(UpdateUI, i);

其实是执行了SynchronizationContext的Post方法。

上面是ExcelDNA里集成的SynchronizationContext实现，有兴趣可以→

尝试实现自定义一个SynchronizationContext
一个SendOrPostCallbackItem实例为一组SendOrPostCallback委托与方法、参数

 internal enum ExecutionType
     {
         Post,
         Send
     }
     internal class SendOrPostCallbackItem
     {
         object state;
         ExecutionType executionType;
         SendOrPostCallback callbackMethod;

         internal SendOrPostCallbackItem(SendOrPostCallback callback, object state, ExecutionType executionType)
         {
             this.callbackMethod = callback;
             this.state = state;
             this.executionType = executionType;
         }

         internal void Execute()
         {
             if (executionType == ExecutionType.Post)
                 Post();
             else
                 Send();
         }
         internal void Send()
         {
             throw new NotImplementedException();
         }

         internal void Post()
         {
             callbackMethod(state);
         }
     }

DiyExcelSynchronizationContext，在ExcelDNA下实现一个SynchronizationContext

 public class DiyExcelSynchronizationContext : SynchronizationContext
    {
        private const string RunMacroName = "ExcelSyncContext.Run";
        private static readonly ConcurrentQueue<SendOrPostCallbackItem> queue = new
    ConcurrentQueue<SendOrPostCallbackItem>();
        private static readonly TimeSpan BackoffTime = TimeSpan.FromSeconds();
        [ExcelCommand(Name = RunMacroName)]
        public static void Run()
        {
            while (true)
            {
                SendOrPostCallbackItem workItem;
                if (!queue.TryDequeue(out workItem))
                {
                    return;
                }
                workItem.Execute();
            }
        }
        dynamic application = ExcelDnaUtil.Application;
        public override void Post(SendOrPostCallback d, object state)
        {

            SendOrPostCallbackItem item = new SendOrPostCallbackItem(d, state, ExecutionType.Post);
            queue.Enqueue(item);
            Task.Factory.StartNew(() =>
            {
                while (true)
                {
                    try
                    {
                        application.Run(RunMacroName);
                        break;
                    }
                    catch (COMException e1)
                    {
                        if (IsRetry(e1))
                        {
                            Thread.Sleep(BackoffTime);
                            continue;
                        }
                        return;
                    }
                    catch (Exception e2)
                    {
                        return;
                    }
                }

            });
        }
        public const uint RPC_E_SERVERCALL_RETRYLATER = 0x8001010A;
        public const uint RPC_E_CANTCALLOUT_INASYNCCALL = 0x800AC472;

        public static bool IsRetry(COMException e)
        {
            var errorCode = (uint)e.ErrorCode;
            switch (errorCode)
            {
                case RPC_E_SERVERCALL_RETRYLATER:
                case RPC_E_CANTCALLOUT_INASYNCCALL:
                    return true;
                default:
                    return false;
            }
        }
    }