ASP.NET invoke workflows and services synchronously/asynchronously

在ASP.NET同步调用workflow或service是比较简单的，直接用workflowInvoker或workflowApplication运行workflow，用生成的代理类调用service中的方法。

异步调用则首先需要在页面指令中添加：

<%@ Page Async="true" %>

然后service可以在添加引用的时候，指定创建异步调用的方法（WCF实现异步执行的方法是另一个话题，这里指的客户端异步的去调用）。

            var proxy = new TestServiceClient();

            proxy.DoWorkCompleted += (o, args) =>
                {
                    if (!args.Cancelled)
                    {
                        this.Trace.Write(string.Format("Completed calling service on thread {0} delay {1}", Thread.CurrentThread.ManagedThreadId, args.Result));
                        this.labelDelay.Text = args.Result.ToString();
                    }
                };

            proxy.DoWorkAsync(delay);

workflow相对复杂一点，需要指定workflow host程序的SynchronizationContext为ASP.NET的当前SynchronizationContext，并显示的开始和结束异步调用

var workflowApplication = new WorkflowApplication(SayHelloDefinition, input)
                {
                    // Tell the workflow runtime we are using the ASP.NET synchronization context  
                    SynchronizationContext = SynchronizationContext.Current,
                    Completed = args =>
                        {
                            this.Trace.Write(
                                string.Format("Completed workflow on thread {0}", Thread.CurrentThread.ManagedThreadId));

                            // Update page controls here  
                            this.labelGreeting.Text = args.Outputs["Greeting"].ToString();

                            // Tell ASP.NET we are finished  
                            SynchronizationContext.Current.OperationCompleted();
                        }
                };

            this.Trace.Write(string.Format("Starting workflow on thread {0}", Thread.CurrentThread.ManagedThreadId));

            // Tell ASP.NET we are starting an async operation  
            SynchronizationContext.Current.OperationStarted();

            workflowApplication.Run();
            // Don't try anything here - it will run before your workflow has completed  

Addition: ASP.NET Tracing 确实提供很多详尽的信息

<%@ Page Trace="true" %>

http://blogs.msdn.com/b/rjacobs/archive/2011/03/16/asp-net-wf4-wcf-and-async-calls.aspx