对HTTP处理程序的同时请求不起作用

I have a Generic HTTP Handler (*.ashx) in my ASP.Net application which performs some basic but time consuming computations printing progress statements to the output as it goes to keep the user informed. Performing these computations involves reading some data files which are locked by the handler while using them, so it's important that two calls to the Handler don't start processing at once.I have a Generic HTTP Handler (*.ashx) in my AS