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Robert Williams is an internet application developer for the Salem Web Network.
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How to disable Full Screen Mode (Silverlight 1.0)

Is there any way to disable the fullscreen mode or disable the double click event for a Media Player built with Microsoft Expression Encoder?

Yes. Edit BasePlayer.js:

Change:

_onFullScreen:function(){var a=this.get_element().content;a.fullScreen=!a.fullScreen} 

To:

_onFullScreen:function(){var a=this.get_element().content;a.fullScreen=false}

I tried various methods to overide this method in the inherited Extended Player Class, but without success. Perhaps there are private member variables that the inherited class cannot access, or perhaps I was doing something wrong. In any case, this method works. If you know of a better one, let me know.


Posted by Williarob on Saturday, December 27, 2008 6:33 PM
Permalink | Comments (1) | Post RSSRSS comment feed

Multi-Threading in ASP.NET

ASP.Net Threading

Inside the ASP.Net Worker Process there are two thread pools. The worker thread pool handles all incoming requests and the I/O Thread pool handles the I/O (accessing the file system, web services and databases, etc.). Each App Domain has its own thread pool and the number of operations that can be queued to the thread pool is limited only by available memory; however, the thread pool limits the number of threads that can be active in the process simultaneously.

  Asp.Net Threading, Threadpools
  Source: Microsoft Tech Ed 2007 DVD: Web 405  "Building Highly Scalable ASP.NET Web Sites by Exploiting Asynchronous Programming Models" by Jeff Prosise.

So how many threads are there in these thread pools? I had always assumed that the number of threads varies from machine to machine – that ASP.NET and IIS were carefully and cleverly balancing the number of available threads against available hardware, but that is simply not the case. The fact is that ASP.Net installs with a fixed, default number of threads to play with: the 1.x Framework defaults to just 20 worker threads (per CPU) and 20 I/O threads (per CPU). The 2.0 Framework defaults to 100 threads in each pool, per CPU. Now this can be increased by adding some new settings to the machine.config file. The default worker thread limit was raised to 250 per CPU and 1000 I/O threads per CPU with the .NET 2.0 SP1 and later Frameworks. 32 bit windows can handle about 1400 concurrent threads, 64 bit windows can handle more, though I don’t have the figures.

In a normal (synchronous) Page Request a single worker thread handles the entire request from the moment it is received until the completed page is returned to the browser. When the I/O operation begins, a thread is pulled from the I/O thread pool, but the worker thread is idle until that I/O thread returns. So, if your page load event fires off one or more I/O operations, then that main worker thread could be idle for 1 or more seconds and in that time it could have serviced hundreds of additional incoming page requests.

  Asp.net Threadpool Saturation
  Source: Microsoft Tech Ed 2007 DVD: Web 405  "Building Highly Scalable ASP.NET Web Sites by Exploiting Asynchronous Programming Models" by Jeff Prosise.

So long as the number of concurrent requests does not exceed the number of threads available in the pool, all is well. But when you are building enterprise level applications the thread pool can become depleted under heavy load, and remember by default heavy load is more than just 200 simultaneous requests assuming a dual CPU Server.

When this happens, new requests are entered into the request queue (and the users making the requests watch that little hour glass spin and consider trying another site). ASP.NET will allow the request queue to grow only so big before it starts to reject requests at which point it starts returning Error 503, Service Unavailable.

If you are not aware of this “Glass Ceiling of Scalability”, this is a perplexing error – one that never happened in testing and may not be reproducible in your test environment, as it only happens under extreme load.

Asynchronous Programming models in ASP.NET

To solve this problem ASP.Net provides four asynchronous Programming models. Asyncronous Pages, Asyncronous HttpHandlers, Asyncronous HttpModules and Asyncronous Web Services. The only one that is well documented and reasonably well known is the asynchronous Web Services model. Since there is quite a lot of documentation on that, and since in future web services should be implemented using the Windows Communication Foundation, we shall concentrate only on the other three.

Let’s begin with the first asynchronous programming model, Asynchronous Pages.

Asynchronous Pages

  Lifecycle of Synchronous/Asynchronous Pages in ASP.NET
  Source: Microsoft Tech Ed 2007 DVD: Web 405  "Building Highly Scalable ASP.NET Web Sites by Exploiting Asynchronous Programming Models" by Jeff Prosise.

To make a page Asynchronous, we insert what we refer to as an “Async Point” into that page’s lifecycle, which you can see in green on the right. We need to write and register with ASP.NET a pair of Begin and End Events. At the appropriate point in the page’s lifecycle, ASP.NET will call our begin method. In the begin method we will launch an asynchronous I/O operation, for example an asynchronous database query, and we will immediately return from the begin method. As soon as we return, ASP.Net will drop the thread that was assigned to that request back into the thread pool where it may service hundreds or even thousands of additional page requests while we wait for our I/O operation to complete.

As you’ll see when we get to the sample code, we return from our begin method an IAsyncResult Interface, through which we can signal ASP.NET when the async operation that we launched has completed. It is when we do that, that ASP.NET reaches back into the thread pool, pulls out a second worker thread and calls our end method, and then allows the processing of that request to resume as normal.

So, from ASP.NET’s standpoint it is just a normal request, but it is processed by 2 different threads; and that will bring up a few issues that we’ll need to discuss in a few moments.

Now, none of this was impossible with the 1.1 framework, but it was a lot of extra work, and you lost some of the features of ASP.NET in the process. The beauty of the 2.0 and later frameworks is that this functionality is built right into the Http pipeline, and so for the most part everything works in the asynchronous page just as it did in the synchronous one.

In order to create an Asynchronous page you need to include the Async=”True” attribute in the page directive of your .aspx file. That directive tells the ASP.NET engine to implement an additional Interface on the derived page class which lets ASP.NET know at runtime that this is an asynchronous page.

What happens if you forget to set that attribute? Well the good news is that the code will still run just fine, but it will run synchronously, meaning that you did all that extra coding for nothing. I should also point out that to make an Asynchronous data call, you also need to add “async=true;” or “Asynchronous Processing=true;” to your connection string – If you forget that and make your data call asynchronously, you will get a SQL Exception.

The second thing we need to do in order to create an asynchronous page is to register Begin and End Events. There are 2 ways to register these events. The first way is to use a new method introduced in ASP.NET 2.0 called AddOnPreRenderCompleteAsync:

using System;

using System.Net;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

 

public partial class temp : System.Web.UI.Page

{

    private static readonly Uri c_UrlImage1 = new Uri(@"http://williablog.net/williablog/image.axd?picture=2010%2f1%2fSlide6.JPG");

    private HttpWebRequest request;

 

    void Page_Load(object sender, EventArgs e)

    {

        request = (HttpWebRequest)WebRequest.Create(c_UrlImage1);

 

        AddOnPreRenderCompleteAsync(

            BeginAsyncOperation,

            EndAsyncOperation

        );

    }

 

    IAsyncResult BeginAsyncOperation(object sender, EventArgs e,

        AsyncCallback cb, object state)

    {

        // Begin async operation and return IAsyncResult

        return request.BeginGetResponse(cb, state);

    }

 

    void EndAsyncOperation(IAsyncResult ar)

    {

        // Get results of async operation

        HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(ar);

        Label1.Text = String.Format("Image at {0} is {1:N0} bytes", response.ResponseUri, response.ContentLength);

    }

}

 


The second way is to use RegisterAsyncTask:

using System;

using System.Net;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

 

public partial class temp : System.Web.UI.Page

{

    private static readonly Uri c_UrlImage1 = new Uri(@"http://williablog.net/williablog/image.axd?picture=2010%2f1%2fSlide6.JPG");

    private HttpWebRequest request;

 

    void Page_Load(object sender, EventArgs e)

    {

        request = (HttpWebRequest)WebRequest.Create(c_UrlImage1);

 

        PageAsyncTask task = new PageAsyncTask(

                BeginAsyncOperation,

                EndAsyncOperation,

                TimeoutAsyncOperation,

                null

            );

 

        RegisterAsyncTask(task);

    }

 

    IAsyncResult BeginAsyncOperation(object sender, EventArgs e,

        AsyncCallback cb, object state)

    {

        // Begin async operation and return IAsyncResult

        return request.BeginGetResponse(cb, state);

    }

 

    void EndAsyncOperation(IAsyncResult ar)

    {

        // Get results of async operation

        HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(ar);

        Label1.Text = String.Format("Image at {0} is {1:N0} bytes", response.ResponseUri, response.ContentLength);

    }

 

    void TimeoutAsyncOperation(IAsyncResult ar)

    {

        // Called if async operation times out (@ Page AsyncTimeout)

        Label1.Text = "Data temporarily unavailable";

    }   

}

 

These methods can be called anywhere in the page’s lifecycle before the PreRender event, and are typically called from the Page_Load event or from the click event of a button during a postback. By the way, you can register these methods from within a UserControl, as long as that control is running on a page that has set the async = true attribute. Again, if it runs on a page without that attribute, the code will still run just fine, but it will run synchronously.

As you can see from just these simple examples, building asynchronous pages is more difficult than building synchronous ones. I’m not going to lie to you. And real world use of these techniques is even more complicated – there is no Business Logic or data layer in the examples above. I don’t want you to leave here believing that you need to make every page asynchronous. You don’t. What I recommend, is doing surgical strikes. Identify that handful of pages in your application that perform the lengthiest I/O and consider converting those into asynchronous pages. The cool thing about this, is that it can improve not only scalability, but also performance, because when you are not holding onto the threads, new requests get into the pipeline faster, they spend less time waiting in that application request queue out there. So, users are happier because pages that they would have had to wait on before – even the ones you have not converted to asynchronous pages, but which might have been delayed while threads were idle, will now load faster. What’s more, as you’ll see in a moment, using RegisterAsyncTask will allow you to perform I/O operations in parallel, which may also improve performance. Having said that, making pages asynchronous is not really about improving performance, it is about improving scalability – making sure that we use the threads in the thread pool as efficiently as we possibly can.

Now I’m sure you are wondering why there are two ways, what the differences are between them, and when you should choose one over the other. Well, there are 3 important differences between AddOnPreRenderCompleteAsync and RegisterAsyncTask.

  1. As we have seen, RegisterAsyncTask allows you to specify a timeout method. It is important to note that the timeout value you specify in the Page Directive of your .aspx page <%@ Page Async="true" AsyncTimeout="5" ... %> is the timeout for ALL asynchronous tasks the page is performing, not 5 secs per async task - all async tasks must be competed within 5 seconds, so be sure to allow enough time here.
  2. If you use AddOnPreRenderCompleteAsync, you may find that some things that worked before, no longer work. For example, if you are using User.Identity.Name in your code to get the authenticated username inorder to personalize a page. If this method is called by the first thread it will work fine. But if you call it on the second thread – in your End method or any of the events that fire after the end method User.Identity.Name will be null. This is because as a Request travels through the ASP.NET Http Pipeline, it is accompanied by an object of type HttpContext that basically encapsulates all of the information that ASP.NET knows about that request. When you use AddOnPreRenderCompleteAsync ASP.NET does not take the extra time to map everything in that context object from thread one to thread two. That’s why User.Identity.Name does not work in thread two. In fact, you will often find that HttpContext.Current is null in thread two. However, if you use RegisterAsyncTask, ASP.Net DOES map everything in that context from thread one to thread two. It does take a few microseconds longer to do this, but it will make your life considerably easier.
  3. The third difference is probably the most important of all. AddOnPreRenderCompleteAsync is a quick and easy way of making a page asynchronous and works well if you have a simple page that needs to perform only 1 asynchronous I/O operation. In real life, a page often needs to perform multiple database queries, or grab data from a webservice and pass it to a database, or something like that. The cool thing about RegisterAsyncTask is that it allows you to quickly and easily queue up multiple Async I/O operations. The last argument is a Boolean value that allows you to specify whether each task can run in parallel. Some times you need to wait for one data call to complete in order to send that data somewhere else, but other times you may need to get data from multiple, unrelated sources and this allows you to fetch them all at the same time, instead of one after the other.

  Controlling Order of Operations
  Source: Microsoft Tech Ed 2007 DVD: Web 405  "Building Highly Scalable ASP.NET Web Sites by Exploiting Asynchronous Programming Models" by Jeff Prosise.

N-Tier Applications

OK. So I expect some of you are thinking “But what if I have a data access layer in my application? My pages can’t go directly to the database, they have to go through that data access layer, or they have to go through my BLL, which calls the Data Access Layer.”

Well, ideally, you should simply add the asynchronous methods to your DAL. If you wrote the DAL yourself or have access to its source code, you should add the Begin and End methods to it Adding the asynchronous methods to your DAL is the best, most scalable solution and doesn’t change the example code much at all: Instead of calling begin and end methods defined inside the page class, you simply call MyDAL.Begin… or MyBll.Begin… when you call RegisterAsyncTask or AddOnPreRenderAsync.

Unfortunately, neither Llblgen nor the Enterprise library (nor LINQ for that matter) supports asynchronous data calls natively. However, I believe that you can modify the generated code in llblgen to enable asynchronous data calls. You could also crack open the source code of the Enterprise library and add the asynchronous methods yourself, but before you try check to see if it has already been done.

Asynchronous HTTP Handlers

The 2nd Asynchronous Programming model in ASP.NET is for HttpHandlers and has been around since .Net 1.x, but was not documented any better in version 2 than it was in version 1. Http Handlers are one of the two fundamental building blocks of ASP.NET, an http handler is an object that is built to handle http requests and convert them into http responses. For the most part, each handler corresponds to a file type. For example, there is a built in handler in ASP.NET that handles .aspx files. It is that handler that knows how to instantiate a control tree and send that tree to a rendering engine. The ASMX Handler knows how to decode SOAP and allows us to build web services.

Basically an HTTP Handler is just a class that implements the IHttpHandler interface, which consists of an IsResuable Boolean function and a ProcessRequest method which is the heart of an httphandler as its job is to turn a request into a response. The ProcessRequest method is passed an HttpContext Object containing all the data asp.net has collected about the request, as well as exposing the Session, Server, Request and Response objects that you are used to working with in page requests.

 

using System.Web;

 

public class HelloHandler : IHttpHandler

{

    public void ProcessRequest(HttpContext context)

    {

        string name = context.Request["Name"];

        context.Response.Write("Hello, " + name);

    }

 

    public bool IsReusable

    {

        get { return true; }

    }

}

 

There are 2 ways to build them. One way is to add the class to your project and register is in the web.config. If you want to register it for any file extension not currently handled by asp.net, you would need to add that extension to IIS. The easier way, is to deploy them as .ASHX files. The ASHX extension has already been registered in IIS, it is auto compiled, no changes are required in the web.config and performance is the same. Ok. So you know what they are and how to build one, when is an appropriate time to use one?

Handlers are commonly used to generate custom XML and RSS feeds, to unzip and render files stored as BLOB fields in the database including image files or logos, HTTP Handlers can also be used as the target of AJAX calls.

A common mistake that programmers new to .net, especially those like myself who came from classic ASP or PHP, is to use the Page_Load event of a page to create a new http response. For example, before I learned about httphandlers, I would use the page load event to create an xml document or a dynamic PDF file and output it to the response stream with a response.End() to prevent the page continuing after I output my file. The problem with that approach is that you are executing a ton of code in asp.net that doesn’t need to execute. When ASP.NET sees that request come in, it thinks it is going to need to build and render a control tree. By pointing the link at the handler instead, you will gain a 10-20% performance increase every time that request is fetched, just because of the overhead you have reduced. Put simply, Http Handlers minimize the amount of code that executes in ASP.NET.

To implement an Asynchronous handler you use the interface IHttpAsyncHandler, which adds BeginProcessRequest and EndProcessRequest methods. The threading works the same way as with an async page. After the begin method is called, the thread returns to the thread pool and handles other incoming requests until the I/O thread completes its work, at which point it grabs a new thread from the thread pool and completes the request.

Page.RegisterAsyncTask cannot be used here, so if you need to run multiple async tasks you will need to implement your own IAsyncResult Interface and pass in your own callbacks to prevent the EndProcessRequest method being called before you have completed all your async operations.

Asynchronous HTTP Modules

HTTP Modules are another fundamental building block of ASP.NET. They don’t handle requests, instead they sit in the HTTP Pipeline where they have the power to review every request coming in and every response going out. Not only can they view them, but they can modify them as well. Many of the features of ASP.NET are implemented using httpmodules: authentication, Session State and Caching for example, and by creating your own HTTP Modules you can extend ASP.NET in a lot of interesting ways. You could use an HTTP Module for example to add google analytics code to all pages, or a custom footer. Logging is another common use of HTTP Modules.

E-Commerce web sites can take advantage of HTTP Modules by overriding the default behavior of the Session Cookie. By default, ASP.NET Session Cookies are only temporary, so if you use them to store shopping cart information, after 20 minutes of inactivity, or a browser shut down they are gone. You may have noticed that Amazon.com retains shopping cart information much longer: You could shut down your laptop, fly to Japan and when you restart and return to Amazon your items will still be there. If you wanted to do this in ASP.NET you could waste a lot of time writing your own Session State Cookie Class, or you could write about 10 lines of code in the form of an HTTP Module that would intercept the cookie created by the Session Object before it gets to the browser, and modify it to make it a persistent cookie. So, there are lots and lots of practical uses for HTTP Modules.

An Http Module is nothing more than a class that implements the IHttpModule Interface, which involves an Init method for registering any and all events that you are interested in intercepting, and a dispose method for cleaning up any resources you may have used.

 

using System;

using System.Web;

 

public class BigBrotherModule : IHttpModule

{

    public void Init(HttpApplication application)

    {

        application.EndRequest +=

            new EventHandler(OnEndRequest);

    }

 

    void OnEndRequest(Object sender, EventArgs e)

    {

        HttpApplication application = (HttpApplication)sender;

        application.Context.Response.Write

            ("Bill Gates is watching you");

    }

 

    public void Dispose() { }

}

 

The events you can intercept in an HTTP Module:

 

  HttpApplication Events 
  Source: Microsoft Tech Ed 2007 DVD: Web 405  "Building Highly Scalable ASP.NET Web Sites by Exploiting Asynchronous Programming Models" by Jeff Prosise.

 Notice the HTTP Handler at the end there that converts the request into a response. These events will always fire in this order, in every request. The Authenticate Request event is the one fired by ASP.NET when a requested page requires authentication. It checks to see if you have an authentication cookie and if you do not, redirects the request to the login page. In the simple example, I was using that End Request event, which is the last one before the response is sent to the browser.

So, that is what HTTP Modules are for, and how they work. Why do we need an Asynchronous version? Well if you really want to see how scalable your application is, add an HTTP Module that makes a synchronous call to a webservice or a database. Since the event you register will be fired on every request, you will tie up an additional thread from the asp.net thread pool on every single request that is just waiting for these I/O processes to complete. So, if you write a synchronous HTTP Module that inserts a record into a database for every single request, and that insert takes 1 second, EVERY single request handled by your application will be delayed by 1 second. So if you need to do any type of I/O from within an HTTP Module, I recommend you make the calls asynchronously and if you are retrieving data, cache it!

To Register Async Event Handlers in an http module - In the Init Method, simply register your begin and end methods using AddOnPreRequestHandlerExecuteAsync:

 

using System.Web;

 

public void Init (HttpApplication application)

{

    AddOnPreRequestHandlerExecuteAsync (

        new BeginEventHandler (BeginPreRequestHandlerExecute),

        new EndEventHandler (EndPreRequestHandlerExecute)

    );

}

 

IAsyncResult BeginPreRequestHandlerExecute (Object source,

    EventArgs e, AsyncCallback cb, Object state)

{

    // TODO: Begin async operation and return IAsyncResult

}

 

void EndPreRequestHandlerExecute (IAsyncResult ar)

{

    // TODO: Get results of async operation

}

Error Handling while multithreading

Errors can happen at any point during the execution of a command. When ASP.NET can detect errors before initiating the actual async operation, it will throw an exception from the begin method; this is very similar to the synchronous case in which you get the exceptions from a call to ExecuteReader or similar methods directly. This includes invalid parameters, bad state of related objects (no connection set for a SqlCommand, for example), or some connectivity issues (the server or the network is down, for example).

Now, once we send the operation to the server and return, ASP.NET doesn’t have any way to let you know if something goes wrong at the exact moment it happens. It cannot just throw an exception as there is no user code above it in the stack when doing intermediate processing, so you wouldn't be able to catch an exception if it threw one. What happens instead is that ASP.Net stores the error information, and signals that the operation is complete. Later on, when your code calls the end method, ASP.Net detects that there was an error during processing and the exception is thrown.

The bottom line is that you need to be prepared to handle errors in both the begin and the end methods, so it is wise to wrap both events in a try – Catch block.

Conclusion

Now you have seen three of the asynchronous programming models ASP.NET has to offer, hopefully I have impressed upon you how important it is to at least consider using them when creating pages that do I/O if you expect those pages to be heavily trafficked. Remember you can also create asynchronous web services. I didn’t cover those here because there is pretty good documentation for that already.

The good thing about Asynchronous Programming models is that it enables us to build scalable and responsive applications that use minimal resources (threads/context switches).

What is the down side? Well it forces you to split the code into many callback methods, making it hard to read, confusing to debug and difficult for programmers unfamiliar with asynchronous programming to maintain.

With this in mind, whenever I add an asynchronous method to an object in the my projects, I also add a traditional Synchronous version. For example, if I had created a BeginUpdatexxx() Method in the BLL, there would also be a traditional Updatexxx() Method, so that if anyone else finds themselves having to use that object, they won’t be left scratching their heads, wondering “how on earth do I use that?”

Asynchronous command execution is a powerful extension to.NET. It enables new high-scalability scenarios at the cost of some extra complexity.

For more information on multi-threading in ASP.NET I highly recommend you read "Custom Threading in ASP.Net".


Posted by Williarob on Tuesday, December 16, 2008 5:30 PM
Permalink | Comments (0) | Post RSSRSS comment feed

Custom Threading in ASP.NET

or "One Mans obsession with finding a way to call synchronous methods asynchronously in ASP.NET".

This is for anyone interested in exploring the System.Threading Namespace in ASP.NET. There are many wrong ways to do it, one right way, and one other way that should only be used when you have no alternative.

First, the wrong ways. As you may or may not know, in .NET you can call any synchronous method asynchronously simply by creating a delegate method and calling the delegate’s BeginInvoke and EndInvoke methods. Knowing this, you might be tempted to try this in ASP.NET. For example, suppose you are using a prebuilt library object that contains the following method which makes a synchronous WebRequest:

        private static readonly Uri c_UrlImage1 = new Uri(@"http://williablog.net/williablog/image.axd?picture=2010%2f1%2fSlide6.JPG");

        private HttpWebRequest request;

        public string Result; // Public Variable to store the result where applicable

 

        public string SyncMethod()

        {

            // prepare the web page we will be asking for

            request = (HttpWebRequest)WebRequest.Create(c_UrlImage1);

 

            // execute the request

            HttpWebResponse response = (HttpWebResponse)request.GetResponse();

            return String.Format("Image at {0} is {1:N0} bytes", response.ResponseUri, response.ContentLength);

        }

Then you read my article on MultiThreading in asp.net and decide that this should be an Asynchronous call. If you don't have easy access to the source code of that prebuilt library, you might be tempted to try this:

 

        public delegate string AsyncMthodDelegate();

 

        public IAsyncResult BeginUpdateByDelegate(object sender, EventArgs e, AsyncCallback cb, object state)

        {

            AsyncMthodDelegate o_MyDelegate = SyncMethod;

            return o_MyDelegate.BeginInvoke(cb, state);

        }

 

        public void EndUpdateByDelegate(IAsyncResult ar)

        {

            AsyncMthodDelegate o_MyDelegate = (AsyncMthodDelegate)((AsyncResult)ar).AsyncDelegate;

            Result = o_MyDelegate.EndInvoke(ar);

            lblResult.Text = Result;

        }

 

        protected void Page_Load(object sender, EventArgs e)

        {

            RegisterAsyncTask(new PageAsyncTask(BeginUpdateByDelegate, EndUpdateByDelegate, AsyncUpdateTimeout, null, false));

        }

 

        public void AsyncUpdateTimeout(IAsyncResult ar)

        {

            Label1.Text = "Connection Timeout";

        }

 

On paper this looks great. You just converted a synchronous method to an asynchronous method and called it using RegisterAsyncTask. In spite of how promising this technique looks, I'm sorry to say that it will do nothing for scalability or performance. Unfortunately, the thread used by BeginInvoke is actually taken from the same worker thread pool that is used by ASP.Net to handle Page Requests, so what you are actually doing is returning the main thread to the thread pool when BeginUpdateByDelegate returns, grabbing a second thread from the same thread pool to call BeginInvoke, blocking that thread until EndInvoke is called, then returning thread two to the thread pool. ASP.NET then pulls a third thread from the same pool to call EndUpdateByDelegate, and complete the request. Net gain: 0 threads, and your code is harder to read, debug and maintain.

 

OK. What about using ThreadPool.QueueUserWorkItem()? You rewrite your code again and now it looks like this:

 

 

        public IAsyncResult BeginThreadPoolUpDate(object sender, EventArgs e, AsyncCallback cb, object state)

        {

            AsyncHelper helper = new AsyncHelper(cb, state);

            ThreadPool.QueueUserWorkItem(ThreadProc, helper);

            return helper;

        }

 

        public void EndThreadPoolUpDate(IAsyncResult AR)

        {

            AsyncHelper helper = (AsyncHelper)AR;

 

            // If an exception occurred on the other thread, rethrow it here

            if (helper.Error != null)

            {

                throw helper.Error;

            }

 

            // Otherwise retrieve the results

            Result = (string)helper.Result;

            lblResult.Text = Result;

        }

 

        protected void Page_Load(object sender, EventArgs e)

        {

            RegisterAsyncTask(new PageAsyncTask(BeginThreadPoolUpDate, EndThreadPoolUpDate, AsyncUpdateTimeout, null, false));

        }

 

        public void AsyncUpdateTimeout(IAsyncResult ar)

        {

            Label1.Text = "Connection Timeout";

        }

 

        class AsyncHelper : IAsyncResult

        {

            private AsyncCallback _cb;

            private object _state;

            private ManualResetEvent _event;

            private bool _completed = false;

            private object _lock = new object();

            private object _result;

            private Exception _error;

 

            public AsyncHelper(AsyncCallback cb, object state)

            {

                _cb = cb;

                _state = state;

            }

 

            public Object AsyncState

            {

                get { return _state; }

            }

 

            public bool CompletedSynchronously

            {

                get { return false; }

            }

 

            public bool IsCompleted

            {

                get { return _completed; }

            }

 

            public WaitHandle AsyncWaitHandle

            {

                get

                {

                    lock (_lock)

                    {

                        if (_event == null)

                            _event = new ManualResetEvent(IsCompleted);

                        return _event;

                    }

                }

            }

 

            public void CompleteCall()

            {

                lock (_lock)

                {

                    _completed = true;

                    if (_event != null)

                        _event.Set();

                }

 

                if (_cb != null)

                    _cb(this);

            }

 

            public object Result

            {

                get { return _result; }

                set { _result = value; }

            }

 

            public Exception Error

            {

                get { return _error; }

                set { _error = value; }

            }

        }

    }

Yikes, this time a helper class was needed to provide the IAsyncResult Interface. Now your code is even more unreadable and I'm sorry to tell you that the thread used by ThreadPool.QueueUserWorkItem also comes from the same thread pool that is used by ASP.Net for handling Requests.

Fine. I'll just use Thread.Start() and create my own thread. Well, you could do that - by creating your own thread, you cannot be stealing one from the ASP.Net threadpool. But not so fast! If you have determined that this method needs to be made asynchronous for reasons of scalability, then this page is under heavy load. Think about that for a second. If you are creating a new thread every time your page is requested and your page is being hammered with 1000 requests a second, then you are creating 1000 new threads almost simultaneously and they are all fighting for CPU time. Clearly using Thread.Start() risks unconstrained thread growth and you can easily find yourself creating so many new threads that the increased CPU contention actually decreases rather than increases scalability, so I don't recommend using Thread.Start() in ASP.Net.

So, you troll the internet looking for other ways.  In the bowels of the System.Threading Namespace, you find the ThreadPool.UnsafeQueueNativeOverlapped method that promises to open up an I/O Completion Port Thread, drawn from the I/O thread pool, just for you to run your method on. So you modify your code again, recompiling with the Allow unsafe code box checked. Now it looks something like this:

 

        public IAsyncResult BeginIOCPUpDate(object sender, EventArgs e, AsyncCallback cb, object state)

        {

            AsyncHelper helper = new AsyncHelper(cb, state);

            IOCP.delThreadProc myDel = SyncMethod;

            IOCP myIOCp = new IOCP(myDel);

 

            try

            {

                myIOCp.RunAsync();

            }

            catch (Exception ex)

            {

                helper.Error = ex;

            }

            finally

            {

                helper.CompleteCall();

            }

            return helper;

        }

 

        public void EndIOCPUpDate(IAsyncResult AR)

        {

            AsyncHelper helper = (AsyncHelper)AR;

 

            // If an exception occurred on the other thread, rethrow it here

            if (helper.Error != null)

            {

                throw helper.Error;

            }

 

            // Otherwise retrieve the results

            Result = (string)helper.Result;

            lblResult.Text = Result;

        }

 

        protected void Page_Load(object sender, EventArgs e)

        {

            RegisterAsyncTask(new PageAsyncTask(BeginIOCPUpDate, EndIOCPUpDate, AsyncUpdateTimeout, null, false));

        }

 

        public void AsyncUpdateTimeout(IAsyncResult ar)

        {

            Label1.Text = "Connection Timeout";

        }

 

        class IOCP

        {

 

            public delegate string delThreadProc();

            private readonly delThreadProc _delThreadProc;

 

            public IOCP(delThreadProc ThreadProc)

            {

                _delThreadProc = ThreadProc;

            }

 

            public void RunAsync()

            {

                unsafe

                {

                    Overlapped overlapped = new Overlapped(0, 0, IntPtr.Zero, null);

                    NativeOverlapped* pOverlapped = overlapped.Pack(IocpThreadProc, null);

                    ThreadPool.UnsafeQueueNativeOverlapped(pOverlapped);

                }

            }

 

            unsafe void IocpThreadProc(uint x, uint y, NativeOverlapped* p)

            {

                try

                {                 

                    _delThreadProc();

                }

                finally

                {

                    Overlapped.Free(p);

                }

            }

 

        }

 

        class AsyncHelper : IAsyncResult

        {

            // Code ommitted for clarity: see above for the full AsyncHelper Class          


        }

 

It seems to work but how can you be sure? You add the following code at various points to test:

            Label1.Text += "<b>EndIOCPUpDate</b><br />";

            Label1.Text += "CompletedSynchronously: " + AR.CompletedSynchronously + "<br /><br />";

            Label1.Text += "isThreadPoolThread: " + System.Threading.Thread.CurrentThread.IsThreadPoolThread.ToString() + "<br />";

            Label1.Text += "ManagedThreadId : " + System.Threading.Thread.CurrentThread.ManagedThreadId + "<br />";

            Label1.Text += "GetCurrentThreadId : " + AppDomain.GetCurrentThreadId() + "<br />";

            Label1.Text += "Thread.CurrentContext : " + System.Threading.Thread.CurrentContext.ToString() + "<br />";

 

            int availWorker = 0;

            int maxWorker = 0;

            int availCPT = 0;

            int maxCPT = 0;

            ThreadPool.GetAvailableThreads(out availWorker, out availCPT);

            ThreadPool.GetMaxThreads(out maxWorker, out maxCPT);

            Label1.Text += "--Available Worker Threads: " + availWorker.ToString() + "<br />";

            Label1.Text += "--Maximum Worker Threads: " + maxWorker.ToString() + "<br />";

            Label1.Text += "--Available Completion Port Threads: " + availCPT.ToString() + "<br />";

            Label1.Text += "--Maximum Completion Port Threads: " + maxCPT + "<br />";

            Label1.Text += "===========================<br /><br />";

 

And you discover that while it does indeed execute on an I/O thread it also uses or blocks a worker thread, perhaps to run the delegate method. In any case, net gain -1 threads - at least with the two previous techniques you were only using a worker thread. Now you are using a worker thread and an I/O thread, and using unsafe code, and your code looks even worse!

So, you think for a while and decide to use a custom threadpool. Perhaps you recall that the folks at Wintellect.com used to offer a free custom threadpool in their PowerThreading Library. You find a copy among your archives and set it up. (The code looks just like the Threadpool.QueueUserWorkItem code above, but it is using the custom thread pool. You add your Code to verify and yes, it does everything you need it to. Available worker Threads = Maximum Worker Threads, Available I/O Threads = Maximum I/O threads. No threads are being stolen from ASP.Net and you don't risk unconstrained thread growth. Short of finding a way to add the asynchronous method to the prebuilt dll (obtaining and modifying the source code - contacting the author/vendor to request asynchronous calls be addedto their library) or switching to your own code, or to another library that already supports asynchronous methods, this is your only option.

The only right way to do asynchronous programming in asp.net is to find a way to add true asynchronous capabilities to your library. If this is impossible, then a custom threadpool is your only option. Now before you rush off to wintellect.com to download this magical solution, I should warn you that the custom threadpool is no longer part of the power threading library. Curious to understand why I contacted the author (Mr Jeffrey Richter) and he told me that he removed the custom thread pool as he believed it promoted poor prgramming practice. He explained that the default number of threads has been greatly increased with the introduction of the 3.x framework (and of course you can increase it in the machine.config), but that ultimately if your library does not support Asynchronous I/O calls, your application will not be scalable.

“If they don’t support async operations then they are not usable for scalable apps – period... Personally, I would not use a [library] that didn't support async operations unless I was using it in a situation where I knew I would always have just a few clients.”

I encourage you to use Asynchronous Delegates and ThreadPool.QueueUserWorkItem freely in console applications and windows forms programs,  just don't bother using them in ASP.Net as it is a waste of time.

So. There you have it. The sample code I used to test which thread pool threads were used in each of the techniques discussed above can be downloaded here. The sample includes a version of Wintellect's Power Threading Library that still contains the Custom Threadpool - look for it in the bin folder.

AsyncThreadTests.zip (264.52 kb)

Note: I recommend you test under IIS 6.0 or IIS 7.0: running on the Casini web server or on IIS 5.1 under windows XP shows inconsistant results.


Posted by Williarob on Tuesday, December 16, 2008 10:19 AM
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Disappearing Quick Launch Toolbar (Windows XP sp3)

If you are running Windows XP Service Pack 3, and also have Google Desktop installed, you may find that every time you reboot, the Quick Launch Toolbar, on the Windows Task bar, vanishes. I found that disabling the Google Desktop toolbar (right click on a blank area of your taskbar, Toolbars > uncheck 'Google Desktop') corrects this issue. If you do not have Google Desktop installed, try this solution:

1. In Registry Editor (Start > Run... > regedit), navigate to:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Winlogon

2. Find the "Userinit" key
3. it probably contains:

%system32%\wsaupdater.exe,

where %system32% represents the path to the System32 folder. For example, C:\Windows\System32

4. Instead of wsaupdater.exe, the data should contain userinit.exe,. Using the example above, change it to:

C:\Windows\System32\userinit.exe,

Do not forget to add the comma at the end!!!

5. Close the Registry Editor and reboot your computer. 


Categories: XP
Posted by Williarob on Tuesday, December 16, 2008 8:12 AM
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Outlook Junk Email Filter Stops Working

After months without a problem, I suddenly found that my Outlook 2003 Inbox was full of Spam and that the junk email box was empty. It was as if the junk email filter had been turned off or the rule deleted. I checked the settings but it all looked normal. The last thing I did the day before was install the Microsoft Expression Suite. A quick web search on Google revealed a lot of other people have noticed their Junk Email filter quit unexpectedly also, some after installing Expression Web which probably uses some Microsoft Office 2007 components. Most of the solutions I found suggested removing the email account and re-adding it, or reinstalling Outlook. Keeping those options in mind as my last resort, I frist tried uninstalling the last Junk Email Filter update that was installed via Microsoft Update. Go to Add/Remove Programs > check the 'Show Updates' Box to find it.), Close Outlook, then run Office Update again to re-install the Junk Email Filter update. It worked. I Hope this saves other people the hassle of reinstalling.

Edit: This just happened again, but this time for a different reason - I had added my own email address to the Safe Recipients list. When you do that, all emails sent to that address will then be automatically marked as "not junk".

To remove yourself from the Safe Recipient list;

  • Tools-> Options…
  • button “Junk E-Mail…”
  • tab “Safe Recipients”
  • Select your own address and press “Remove”

Posted by Williarob on Tuesday, December 16, 2008 7:20 AM
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Delayed Automatic Exit from Console Application v2.0

This is an alternate version to the one originally posted here. It occurred to me that if someone was actually at the console and the program quit without warning, while allegedly waiting for a key press, that would be a bit surprising and/or annoying. This new version displays a warning with an on screen count down leading up to the automatic exit:

 

    1 using System;

    2 using System.Threading;

    3 

    4 namespace ConsoleApplication1

    5 {

    6     class Program

    7     {

    8         static void Main(string[] args)

    9         {

   10             //... code here for whatever your console app does

   11             Console.WriteLine("[Result of the Program]" + Environment.NewLine);

   12 

   13             Console.WriteLine("...press any key to exit." + Environment.NewLine);

   14 

   15             delay = new ExitDelay();

   16             delay.Start();

   17             MyTimer = new Timer(TimesUp, null, 1000, 1000);

   18         }

   19 

   20         static ExitDelay delay;

   21         static Timer MyTimer;

   22         static int CountDown = 10;

   23 

   24         // Timer callback: they didn't press any key, but we don't want this window open forever!

   25         private static void TimesUp(object state)

   26         {

   27             if(CountDown > 0)

   28             {

   29                 Console.CursorLeft = 0;

   30                 Console.Write("Program will exit automatically in " + CountDown + " ");

   31                 CountDown--;

   32             }

   33             else

   34             {

   35                 Console.CursorLeft = 0;

   36                 Console.WriteLine("Exiting - Bye!                                   ");

   37                 Thread.Sleep(1000);

   38                 delay.Stop();

   39                 MyTimer.Dispose();

   40                 Environment.Exit(0);

   41             }

   42         }

   43 

   44     }

   45 

   46     public class ExitDelay

   47     {

   48         private readonly Thread workerThread;

   49 

   50         public ExitDelay()

   51         {

   52             this.workerThread = new Thread(this.work);

   53             this.workerThread.Priority = ThreadPriority.Lowest;

   54             this.workerThread.Name = "ExitTimer";

   55         }

   56 

   57         public void Start()

   58         {

   59             this.workerThread.Start();

   60         }

   61 

   62         public void Stop()

   63         {

   64             this.workerThread.Abort();

   65         }

   66 

   67         private void work()

   68         {

   69             Console.ReadKey();

   70             this.Stop();

   71         }

   72     }

   73 

   74 }

 


Categories: VB
Posted by Williarob on Saturday, December 13, 2008 12:08 PM
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Traditional Console Spinner

Add this class to your console application, to assure the users that long running tasks are still working.

 

    1 Imports System.Threading

    2 

    3 Public Class ConsoleSpinner

    4     ' Methods

    5     Public Sub New(ByVal ProcessingMsg As String, ByVal FinishedMessage As String)

    6         Me.processingMessage = ProcessingMsg

    7         Me.finishedMessage = FinishedMessage

    8         Me.workerThread = New Thread(New ThreadStart(AddressOf Me.Spin))

    9         Me.workerThread.Priority = ThreadPriority.Lowest

   10         Me.workerThread.Name = "ConsoleSpinner"

   11     End Sub

   12 

   13     Private Sub Spin()

   14         Dim index As Integer = 0

   15         Do While (1 <> 0)

   16             Console.Write(ChrW(13) & "{0} {1}", Me.processingMessage, ConsoleSpinner.anim(index))

   17             index += 1

   18             If (index >= ConsoleSpinner.anim.Length) Then

   19                 index = 0

   20             End If

   21             Thread.Sleep(100)

   22         Loop

   23     End Sub

   24 

   25     Public Sub Start()

   26         Me.workerThread.Start()

   27     End Sub

   28 

   29     Public Sub [Stop]()

   30         Me.workerThread.Abort()

   31         Console.WriteLine("")

   32         Console.WriteLine(Me.finishedMessage)

   33     End Sub

   34 

   35 

   36     ' Fields

   37     Private Shared anim As String() = New String() {"|", "/", "-", "\", "|", "/", "-", "\"}

   38     Private finishedMessage As String

   39     Public processingMessage As String = String.Empty

   40     Private workerThread As Thread

   41 End Class

Call it from any point in your main program using:

   Dim cs As New ConsoleSpinner("Working...", "Done.")

   cs.Start()
  

   ' Do Something that may take a while...

 

   cs.Stop()

 


Categories: VB
Posted by Williarob on Saturday, December 13, 2008 7:10 AM
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Delayed Automatic Exit from Console Application

Suppose you need to write a console application that will run as a scheduled task on a busy production server, but you want to delay the exit so that they can read the results on the screen, but not force someone to push a key, as there may not always be someone at the console to do so. Ending with Console.ReadKey() is no good as it will wait until you push a key before it exits. Here is my solution:

 

    1 using System;

    2 using System.Threading;

    3 

    4 namespace ConsoleApplication1

    5 {

    6     class Program

    7     {

    8         static void Main(string[] args)

    9         {

   10             //... code here for whatever your console app does

   11 

   12             Console.WriteLine("Press any key to exit...");

   13 

   14             delay = new ExitDelay();

   15             delay.Start();

   16             MyTimer = new Timer(TimesUp, null, 10000, Timeout.Infinite);

   17         }

   18 

   19         static ExitDelay delay;

   20         static Timer MyTimer;

   21 

   22         // Timer callback: they didn't press any key, but we don't want this window open forever!

   23         private static void TimesUp(object state)

   24         {

   25             delay.Stop();

   26             MyTimer.Dispose();

   27             Environment.Exit(0);

   28         }

   29 

   30     }

   31 

   32     public class ExitDelay

   33     {

   34         private readonly Thread workerThread;

   35 

   36         public ExitDelay()

   37         {

   38             this.workerThread = new Thread(this.work);

   39             this.workerThread.Priority = ThreadPriority.Lowest;

   40             this.workerThread.Name = "ExitTimer";

   41         }

   42 

   43         public void Start()

   44         {

   45             this.workerThread.Start();

   46         }

   47 

   48         public void Stop()

   49         {

   50             this.workerThread.Abort();

   51         }

   52 

   53         private void work()

   54         {

   55             Console.ReadKey();

   56             this.Stop();

   57         }

   58     }

   59 

   60 }

 

This gives someone 10 seconds to read the result and press a key before exiting the application automatically.

Edit: A newer Version of this technique us available . The new Version provides an on screen countdown, notifying the user that the program is about to exit - otherwise if there is someone at the console and it suddenly quits while instructing them to hit any key to quit, that might be a bit worrying! I leave this example here because it is a good example of how start and stop a new Thread as well as how to use the System.Threading.Timer Class in a slightly different way to the new version which uses polling.


Categories: C# | Multithreading
Posted by Williarob on Friday, December 12, 2008 6:12 PM
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Windows Update Site Not Working

If you have a Laptop that is normally attached to your company's Network Domain, you may find that when you are roaming in the field, the Windows Update site does not work. The reason for this is simple. The group policies of your domain force your laptop to obtain its updates from the local network, rather than the internet. However, if you are rarely connected to the domain, this makes checking for optional updates rather difficult. One solution that I found to work is to manually re-register the Windows update components.

Click Start > Run > Type the follow commands in the box (one at a time, in sequence): 

REGSVR32 C:\WINDOWS\system32\wuapi.dll

REGSVR32 C:\WINDOWS\system32\wuauclt.exe

REGSVR32 C:\WINDOWS\system32\wuaueng.dll

REGSVR32 C:\WINDOWS\system32\atl.dll

REGSVR32 C:\WINDOWS\system32\wucltui.dll

REGSVR32 C:\WINDOWS\system32\wups.dll

One of these may not appear to work properly, but nevertheless, the whole sequence solved the problem for me.


Categories: XP
Posted by Williarob on Wednesday, December 10, 2008 7:38 AM
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Virtual PC Cannot Access Host Via Network

I just installed Microsoft Virtual PC on Windows Vista Ultimate x64 sp1. I then installed Windows XP sp3 into a new Virtual Machine. The Virtual XP machine could not access the network shares on the host. It could access shares on other PCs in my workgroup, and I verified that file and print sharing, public folder sharing, firewall settings, etc. on the host was all correctly configured. The workgroup name matched, it could even see the host, but kept giving me an error that I did not have permission to access this resource, and suggested I contact the administrator - not much help when you are the administrator.

In my case, the solution was to increase the IRPStackSize value in the registry:

  1. Backup your Registry!
  2. Run regedit.
  3. Navigate to the following key: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\LanmanServer\Parameters
  4. In the right pane, double-click the IRPStackSize value.

    NOTE If the IRPStackSize value does not already exist, use the following procedure to create it:
    •  In the Parameters folder of the registry, right-click the right pane.
    • Point to New, and then click DWord Value.
    • Type IRPStackSize.

      IMPORTANT: Type "IRPStackSize" exactly as it is displayed because the value name is case-sensitive.

  5. Change the Base to decimal.
  6. In the Value Data box, type a value that is larger than the value that is listed. If you created the IRPStackSize value using the procedure described in step 4, the default value is 15. It is recommended that you increase the value by 3. Therefore, if the previous value was 11, type 14, and then click OK.
  7. Close the Registry Editor and restart the computer.

If the problem persists after you complete the preceding procedure, try to increase the value of IRPStackSize even more. The maximum value is 50 (0x32 hex). I expect that this solution would also work for similar problems encountered when running a virtual machine in VMware.


Categories: Virtualization
Posted by Williarob on Wednesday, December 03, 2008 6:26 PM
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