Alik Levin's : Threading

Improve ASP.NET 2.0 Performance With PageAsyncTask - Multithreading For The Masses

alikl — Thu, 02 Oct 2008 11:31:38 GMT

Multithreading is tough. This is what John Robbins says about it in his excellent book Debugging Microsoft .NET 2.0 Applications:

"Don't do it... Make sure there's no other way you can structure your program before you decide to incorporate multithreading into your application... you are easily adding a minimum of an extra month of development and testing to your schedule". I agree with it completely. But there are times multithreading is unavoidable. Especially when more and more Services popping up in the wild...

From Asynchronous Pages in ASP.NET 2.0

Customer Case Study

I am working with the customer to improve their ASP.NET 2.0 application performance. The application issues multiple requests to the backend middleware that is exposed as a web service. The application cannot get a hold on the actual proxies rather it is provided with the components that wrap the web services proxies. The application needs to issue concurrent requests. Serial request would result in serious latency which is unacceptable by end users.

Analysis

Since we cannot get hold on web services proxies we cannot utilize available asynchronous methods available with it: BeginMyMethod/EndMyMethod and MyMethodAsync/MyMethodCompleted. But we definitely can utilize another option available with ASP.NET 2.0 - registering asynchronous tasks using PageAsyncTask class.

The following information is based on the following materials:

PageAsyncTask Implementation Steps

This is the summary of the steps to implement and register PageAsyncTask:

Create a class that contains lengthy operation
Declare AsyncTaskDelegate
Add OnBegin, OnEnd, OnTimeout methods to the class
Mark the calling page as Async="true"
Register the PageAsyncTasks in the ASPX page and execute it

You can grab the Visual Studio 2008 project with the implementation from my SkyDrive here:

Related Materials

This template is made with PracticeThis.com plugin for Windows Live Writer

Improve ASP.NET Performance With Multithreading Using Thread Or ThreadPool Objects

alikl — Mon, 23 Jun 2008 13:27:12 GMT

Your ASP.NET application performs slower than expected? How many times do you access your database for each request? Did you use SQL Profiler to find out? Did you know that chatty database access is one of the most common performance sins (this is my own observation)?

Want to improve? - Reduce the number of database queries.

Not an option? - You may want using multithreading. Proceed with caution.

Real world scenario

You need to run 3 independent heavy database queries – Q1, Q2, Q3. You need to use the result from the three – Result = Q1+Q2+Q3. You never know the order in which each query completes. It can be: Q1Q2Q3, Q1Q3Q2, Q2Q3Q1, Q2Q1Q3, Q3Q2Q1, Q3Q1Q2. Missed any combination? Run one after another would create significant latency. Running each on its own thread would create latency of Max(Q1,Q2,Q3) which is less that sum of the three.

How to run each query on its own thread and wait for the completion for each one?

Using Thread object

The following code spawns three threads and waits for all to join, and then use the results from each.

   1: Thread t1 = new Thread(DoWork1);

   2: t1.Start();

3:

   4: Thread t2 = new Thread(DoWork2);

   5: t2.Start();

6:

   7: Thread t3 = new Thread(DoWork3);

   8: t3.Start();

9:

  10: t1.Join(1000);

  11: t2.Join(1000);

  12: t3.Join(1000);

13:

14:

  15: Label1.Text = (i1 + i2 + i3).ToString();

See any issues using it in ASP.NET? One caveat though, creating threads manually like this may cause performance hit as it involves context switching – CPU consuming operation. Consider using ThreadPool object.

Using ThreadPool object (preferred, but are you using COM?)

ThreadPool is preferred as it already has live threads allocated for you. No need to ask for a favor from CPU in the moment of truth. Here is the code:

   1: public partial class _Default : System.Web.UI.Page

   2: {

   3:     int i1 = 0;

   4:     int i2 = 0;

   5:     int i3 = 0;

6:

   7:     WaitHandle[] waitHandles = new WaitHandle[]

   8:         {

   9:             new ManualResetEvent(false),

  10:             new ManualResetEvent(false),

  11:             new ManualResetEvent(false)

  12:         };

13:

14:

  15:     protected void Page_Load(object sender, EventArgs e)

  16:     {

17:

  18:     }

19:

  20:     protected void Button1_Click(object sender, EventArgs e)

  21:     {

  22:         Stopwatch sw = new Stopwatch();

23:

  24:         sw.Start();

25:

  26:         WaitCallback method1 = new WaitCallback(DoWork1);

  27:         bool isQueued1 = ThreadPool.QueueUserWorkItem(method1, waitHandles[0]);

28:

  29:         WaitCallback method2 = new WaitCallback(DoWork2);

  30:         bool isQueued2 = ThreadPool.QueueUserWorkItem(method2, waitHandles[1]);

31:

  32:         WaitCallback method3 = new WaitCallback(DoWork3);

  33:         bool isQueued3 = ThreadPool.QueueUserWorkItem(method3, waitHandles[2]);

34:

  35:         if (WaitHandle.WaitAll(waitHandles, 5000, false))

  36:             Label1.Text = (i1 + i2 + i3).ToString();

  37:         else

  38:             Label1.Text = "Problem";

39:

  40:     }

41:

  42:      void DoWork1(object state)

  43:     {

  44:         int.TryParse(TextBox1.Text, out i1);

45:

  46:         //HEAVY QUERY GOES HERE. Sleep is for the demo only! Remove it!

  47:         Thread.Sleep(i1);

  48:         ManualResetEvent mre = (ManualResetEvent)state;

  49:         mre.Set();

50:

  51:     }

52:

  53:      void DoWork2(object state)

  54:     {

  55:         int.TryParse(TextBox2.Text, out  i2);

56:

  57:         //HEAVY QUERY GOES HERE. Sleep is for the demo only! Remove it!

  58:         Thread.Sleep(i2);

  59:         ManualResetEvent mre = (ManualResetEvent)state;

  60:         mre.Set();

  61:     }

62:

  63:      void DoWork3(object state)

  64:     {

  65:         int.TryParse(TextBox3.Text, out  i3);

66:

  67:         //HEAVY QUERY GOES HERE. Sleep is for the demo only! Remove it!

  68:         Thread.Sleep(i3);

  69:         ManualResetEvent mre = (ManualResetEvent)state;

  70:         mre.Set();

  71:     }

72:

  73: }

Caveat

If your function calls on COM object – avoid using ThreadPool, its Apartment model is not compatible with COM and it cannot be changed. More info - Pitfalls With .Net Multithreading And COM Objects – Threads Must Have Compatible Apartment Models (MTA vs. STA).

Another point to call out is that performance improvements based on multithreading is subject to amount of available CPU’s. Test your solution first!

This post was written with help from Lior, MCS Israel Architect.

Download sample project with the code from my SkyDrive:

Enjoy.

Pitfalls With .Net Multithreading And COM Objects – Threads Must Have Compatible Apartment Models (MTA vs. STA)

alikl — Fri, 20 Jun 2008 10:09:11 GMT

Be alert when implementing multithreading .Net in conjunction with COM objects. Thread apartment models matter.

.Net threads have Multi Threaded Apartment (MTA) model by default. COM objects have Single Thread Apartment (STA). Calling on COM objects on .Net threads that you spawn may cause unpredicted result.

Multithreading in .Net is easily implemented based on either Thread or ThreadPool objects. Thread.Start() method spawns new thread which has Multi Threaded Apartment (MTA) model . ThreadPool.QueueUserWorkItem(myMethod) queues myMethod to be executed on available thread managed by it.

Thread object and COM

When spawning your own threads with Thread.Start() set Thread’s apartment model to STA if you plan calling COM object on it:

        1: Thread t = new Thread(DoWork);

       2: t.SetApartmentState(ApartmentState.STA);

       3: t.Start();

Note, spawning your own threads with Thread.Start() utilizes resources – mainly CPU, spawning too much threads may cause performance hit. Consider using ThreadPool object.

ThreadPool object and COM

All threads managed by ThreadPool objects are MTA threads. Apartment model of ThreadPool’s threads cannot be changed. Do not call COM objects on ThreadPool’s threads.

Possible designs and solutions

ASP.NET. Calling COM objects in ASP.NET pages configure AspCompat=true:

“Most COM components will work with ASP.NET…”

“…The AspCompat attribute forces the page to execute in STA mode. The runtime throws an exception if the compatibility tag is omitted and an STA component is referenced on the page.”

Client side (like WinForms)multithreading. Use ThreadPool with its MTA threads. Spawn another thread with Thread.Start() setting its apartment model to STA.
Custom server side multithreading. I’d consider using Remoting infrastructure. In case your server application should serve messages that are not covered by Remoting’s built in mechanisms I’d consider building my own Channel sink.
And the last but not the least. Do not forget to call Marshal.ReleaseComObject(obj) to dispose the COM objects created on your the threads.