Superior ways to a better UI

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Developing Windows and Web Applications using
Visual Studio.NET
Presented by Paul Sorauer
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Admin Stuff

• Attendance
• You initial sheet
• Hands On Lab
• You get us to initial sheet
• Homework
• Certificate
• At end of 10 sessions
• If we say you have completed successfully ?

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Session 5 Web Services Threading

• Agenda
• What are Web Services?
• WCF Services
• Consuming Web Services
• Threading

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What are Web Services?

• A web service is a collection of protocols and
  standards used for exchanging data between
  applications or systems. Software applications
  written in various programming languages and
  running on various platforms can use web services
  to exchange data over computer networks like the
  Internet in a manner similar to inter-process
  communication on a single computer. (Wikipedia)
• Technologies that underpin Web Services are XML
  and SOAP.
• Cross Platform
• E.g. Java Web Service (AXIS) can by consumed by a
  .NET application and vica versa

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Web Services

• There are many web services available on the Web,
  and there are Web Services APIs for popular
  applications such as
• Google (http//code.google.com/apis/)
• Facebook (http//developers.facebook.com/)
• Virual Earth (http//msdn2.microsoft.com/en-us/vir
  tualearth/default.aspx)
• TV Guides (http//d1.com.au/D1xmltv.asmx)

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Creating a Web Service

• Built in Web Services Project
• WebMethod attribute to expose methods
• WSDL File (wiz-dull)

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Web Services
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Web Service Interface - SOAP

• Built in test site for simple data types
• Shows the expected SOAP request and SOAP response

SOAP Request
SOAP Response
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Telnet Demo

• Craft a SOAP packet and send it to the web
  service via telnet
• See the response

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Web Services Definition Language

• Defines the methods, results and types in an XML
  document
• There are proxy generators (wsdl.exe) that take
  the WSDL file and generate a Web Service Client
  based on the WSDL

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Consuming Web Services

• Automatic - Add a Web Reference to your client
• Dynanically generates a web service client class
  with all the exposed methods
• Synchronous and Asynchronous methods
• Manual - Run wsdl.exe

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Windows Communication Foundation (WCF)

• Part of the .NET Framework 3 (Formerly WinFX)
• Windows Presentation Foundation (WPF)
• Windows Communication Foundation (WCF)
• Windows Workflow (WF)
• Cardspace
• WCF isnt just a web service
• Supports many transport protocols, HTTP, UDP, TCP
• Supports queues, transactions, reliable sessions,
  better security model

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Windows Communication Foundation (WCF)

• WCF Sites for more info
• http//wcf.netfx3.com/

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WCF Demo

• Creating a WCF Service
• Hosting a WCF Service
• Consuming a WCF Service

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Threading

• Why do we need threading?
• Blocking calls (e.g. Disk IO, Network)
• Responsive UI
• Better performance (especially on multi-core
  processors)

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How do I create a Multi threaded application?

• Application.DoEvents
• Thread.Start
• Delegate.BeginInvoke
• BackgroundWorker

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Application.DoEvents()

• Call this method inside code that is being
  processed
• What it does is it issues a command to the UI to
  process events on the message queue (e.g. Mouse
  Clicks, Redraw Window)

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Application.DoEvents()

• Not appropriate
• Ideal scenario is

Worker 1
SearchGoogle()
UI
Return
FetchData
Worker 2
Merge
SearchYahoo()
Done
Return
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Creating a new thread

• Threading control through the System.Threading
  namespace
• Create a delegate for the method you want to set
  as the start location of threads execution
• Create a new thread using this delegate
• Start the thread

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Creating a new thread

• using System.Threading
• private void btnSearch_Click(object
  sender, EventArgs e)
• // Tell the thread starter which
  method to use (i.e. StartSearch)
• ThreadStart ts new
  ThreadStart(StartSearch)
• // Create a new thread
• Thread SearchThread new Thread(ts)
• // Start the search on the new thread
• SearchThread.Start()
• public void StartSearch()

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System.Threading.Thread

• System.Threading.Thread is the main class for
  creating threads and controlling them. A few
  interesting methods are shown below
• Start() starts the execution of the thread.
  
  
• Suspend() suspends the thread, if the thread
  is already suspended, nothing happens.
• Resume() resumes a thread that has been
  suspended.
• Interrupt() interrupts a thread that is in the
  wait, sleep or join stage.
• Join() blocks a calling thread until the
  thread terminates.
• Sleep(int x) suspends the thread for
  specified amount of time (in milliseconds).
  
• Abort() Begins the process of terminating the
  thread. Once the thread terminates,
  it cannot be restarted by calling the
  function Start() again.

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Thread.Start()

• The UI was responsive
• Was no longer a blocking call could continue
  working while search ran
• Allows multiple worker threads to execute
  simultaneously
• Bad coding practice for threads no guarantee
  that you will capture all errors

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Thread.Start()

• Suitable (not the best solution)

Worker Thread
UI Thread
Start
Start
Execute
Update UI
Done
Done
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Delegate.BeginInvoke()

• Ideal scenario is

Worker 1
SearchGoogle()
Return
FetchData
Worker 2
Merge
SearchYahoo()
Done
Return
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Delegate.BeginInvoke()

• Best Solution Using Delegates to execute a
  method asynchronously.
• What is a delegate?
• A delegate defines both the signature and the
  location of a specified method.
• The .NET Framework provides a series of delegates
  for commonly used syntaxes.
• Delegates can be used to call methods
  asynchronously, for example using
  Delegate.BeginInvoke().This uses a worker thread
  from the managed Threadpool.

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Delegate.BeginInvoke()

• The UI was completely responsive
• UI updates are no longer tightly bound (event
  based)

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Delegate.BeginInvoke()

• The perfect solution

Worker 1
SearchGoogle()
Return
FetchData
Worker 2
Merge
SearchYahoo()
Done
Return
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An Easier Way

• BackgroundWorker Component
• Uses Delegates under the covers
• Sites to Research
• http//msdn2.microsoft.com/en-us/library/system.co
  mponentmodel.backgroundworker(vs.80).aspx
• http//www.codeplex.com/ExerciseBackgroundW
• http//www.codeguru.com/columns/vb/article.php/c10
  755/

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• The One Golden Rule

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The One Golden Rule

• When Multiple threads access a shared resource,
  only 1 thread can update it at a time.
• Otherwise we get
• Deadlocks
• Race Conditions
• Correct use of Synchronisation prevents these
  situations

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Synchronization Shared Resources

• Synchronisation involves controlling access to a
  shared resource so only one thread can access the
  resource at a time.
• Resources include
• Variableseg. Arrays
• User Interface Controls eg. Progress Bar

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Synchronizing Variables

• There are several methods of Synchronizing access
  to Variables
• Lock() code Only one thread executes the
  code inside the braces at a
  time.
• Monitors - lock a section of code so only one
  thread can access it at a time.
• Interlocked Class basic atomic operations on a
  single integer variable
• ManualResetEvent and AutoResetEvent - allow one
  thread to notify others of an event occurring
• WaitHandles thread waits on a certain event to
  occur before continuing
• And more

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Lock

• public static Array myArray
• public void UpdateArray()
• lock (myArray)
• // Do something here to the shared
  resource
• myArray.Add(10)

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Using a Monitor

• public static string c
• public void some_method()
• int a100
• int b0
• Monitor.Enter(c)
• //say we do something here.
• c(a/b).ToString()
• Monitor.Exit(c)

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Synchronizing User Interface

• Synchronization problem solved in VS 2005 by only
  allowing the main UI thread to access UI
  controls.
• Worker threads must tell the UI thread to make a
  change on their behalf via a delegate.

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• A Real World Example
• SSW Link Auditor

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Link Auditor
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Link Auditor

• Threading was used to achieve
• A responsive UI throughout
• Optimize the scanning process
• Techniques that we used
• Delegates and Callbacks
• ManagedThreadPool class

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Session 5 Threading

• Summary
• What is Threading?
• Application.DoEvents ()
• Thread.Start ()
• Synchronization
• Delegate.BeginInvoke()
• Generate custom events
• Delegates

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Thank You!