Web services, WCF services and Multi Threading with Windows Forms

Delivering Awesome Web Applications

Developing Windows and Web Applications using Visual Studio.NET

Peter Gfader

Senior Software Architect

Homework?

Deploy your homework from week2 via ClickOnce to your local IIS.

Show me the screen of ClickOnce: Properties in WinformsUI, “Publish”, “Application Files”

Question

How can you get version 1.5 again if you rolled back from version 1.6?

Do you get it automatically?

N-Tier Application

Deployment

ClickOnce

Security

Session 4: Last week?

What are Web Services?

WCF Services

Consuming Web Services

Threading

Do the lab

Review

Session 5: WCF and Multi-Threading

SSA @ SSW

Loves C# and .NET (Java not anymore)

Specializes in Windows Forms ASP.NET TFS testing Automated tests Silverlight

Peter Gfader

Web services

Wikipedia

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

What are Web Services?

The technologies that underpin Web Services are XML SOAP (Simple Object Access Protocol) This is a way of sending around objects over a

network

Cross Platform e.g. Java Web Service (AXIS) can be consumed by

a .NET application and vice versa

What are Web Services?Con'd

There are many public web services available on the Web, and there are Web Services APIs for popular applications such as: Google http://code.google.com/apis/ Amazon http://en.wikipedia.org/wiki/Amazon_Web_Services Facebook http://developers.facebook.com/ Virtual Earth http://msdn2.microsoft.com/en-us/virtualearth/default.aspx Microsoft, new to the party with Azure:

http://www.microsoft.com/azure/default.mspx More here

• http://www.service-repository.com/

Public Web Services

Building block for building Connected Systems

Designed around messages!

Support for all standards/specifications around messaging (particularly driven by WS-*)

Consistent API regardless of messaging requirement

Supports variety of transport and encoding configurations

Messaging standard is SOAP but this is not the only option

Extensibility model allows for any custom requirements/encoders/channels to be developed

Not just “Web Services”

Supports transport protocols, HTTP Web services UDP User Datagram Protocol TCP Transmission Control Protocol

Supports Queues MSMQ (Microsoft Message Queue) Transactions Reliable sessions Better security model

http://prezi.com/tg2kaukw8sez/wcf-intro/

Windows Communication Foundation (WCF)

Endpoint

Address where the WCF service is available from

Binding how to get access to the WCF service

Contract what the WCF service can do Behavior how the service will behave locally

(e.g. debugging)

Definitions

Built in WCF Service Project

Define the service with ServiceContract Define methods with OperationContract

Creating a WCF Service

Define a contract

namespace wcfRemoteCalc { // Note this is derived from Calculator.cs public enum FunkType { Unknown , Add , Subtract , Multiply, Divide, SafeDivide } [ServiceContract] public interface IService1 { [OperationContract] int calculate( FunkType aFunction , int aNumb1, int aNumb2 ); } }

Contract(IService.cs)

It means INTERFACE

Define an Interface contract

Contract

Implementation

Implement the contract

Automatic - Add a Web Reference to your client Dynamically generates a web service client class

with all the exposed methods Synchronous and Asynchronous methods Silverlight:

All web service method calls are Asynchronous

Consuming Web Services

Creating

Consuming

Configuring

WCF Service Demo (The LAB)

Multithreading in .Net

Why do we need threading?

Blocking calls (e.g. Disk IO, Network) on long running-tasks

Responsive User Interface (UI)• E.g. Windows Desktop Search

Better performance (especially on multi-core processors)

Threading

Application can spawn one or more processes

Processes have isolation, separation of

Data Memory Resources

Processes contain Threads

Processes

Windows is a Pre-emptive multitasking operating system

The O/S is responsible for managing timeslices (quantums) between different processes

The Kernal switches/schedules execution code between threads

UNIX is a true cooperative multi-tasking operating system

Processes instruct the O/S when to switch contexts This is brittle since a poorly written application can hang

the system by never allowing other processes to run

Threading and the O/S

System.Threading

Background Worker

“Threadsafe” classes (particularly collections)

Thread Synchronisation

Interprocess communication

AppDomain

STA (Single Threaded Apartment) Model

Threading in .Net

1. Cannot Interact with UI Elements from a thread that it did not create (the UI object is not accessible to the other thread)

2. Some classes are not Threadsafe, meaning that data may be overwritten/corrupted (e.g. Data collections)

3. Cannot predicate the sequence when separate threads will finish their work

Important Concepts

Application.DoEvents

System.Threading

Thread.StartDelegate.BeginInvoke

BackgroundWorker component

Threading in WinForms (bad to good)

Call this method inside long running code that is being processed

What it does is it issues a command to the UI to process pending events on the message queue e.g.

Mouse Clicks Redraw Window etc

Application.DoEvents()

FetchData

SearchGoogle()

Return

Worker 1

SearchYahoo()

Return

Worker 2

Do Events processes all Window Messages in the queue until it has run out of messages (click, paint, focus, etc.)

In an example of loading a Listbox with items:

What happens if the user clicks the close button? Ooops! IndexOutOfRangeException! Clicking on the close

box has invoked the form’s Dispose method, which has cleared the control collection. What's worse is that clicking close on the form didn't stop the list box processing from finishing up - while the form was no longer visible, this handler was merrily keeping the application alive.

Why wouldn’t this normally happen?The action of the user pressing the close button would not be processed until you’ve returned from the handler for the button click.

DoEvents is Bad!

GOOD BAD usage of DoEvents

Application.Run

Process mouse up on button

Fire ButtonClick event

Add bunch of items to listbox

Update the first control on the form

Process mouse up on close box

Dispose the form

Application.Run

Process mouse up on button

Fire ButtonClick event

Add some items to listbox

Call Application.DoEvents to make it look more responsive

Process mouse up on close box

Dispose the form

Add remaining items to listbox

Update the first control on the form -- BOOM! Controls collection has been cleared!

BackgroundWorker Component

Uses Delegates under the covers

Sites to Research http://msdn2.microsoft.com/en-us/library/system.compone

ntmodel.backgroundworker(vs.80).aspx http://www.codeplex.com/ExerciseBackgroundW http://www.codeguru.com/columns/vb/article.php/c10755/

An Easier Way

Synchronization problem solved in VS 2005 (and later) 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.

Synchronising User Interface

Makes life easy in .Net!

No complex code needed only need to implement a few methods:

DoWork RunWorkCompleted ProgressChanged

Background Worker Component

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

The One Golden Rule

Synchronisation involves controlling access to a shared resource so only one thread can access the resource at a time.

Resources include:

Variables e.g. Arrays

User Interface Controls e.g. Progress Bar

Synchronization & Shared Resources

Windows WorkFlow (WF) parallel task execution

WF is explcitly designed for long-running tasks

PLINQ (Parallel Linq) .Net 4.0

UI Control Virtual Mode

You control how the data is retrieved into the control when it needs to display

Use this if you have a 1 million rows in memory, but can only display 50 at a time (similar to paging in a webform)

Other .Net multi-threading Technologies and Concepts

Threading in .NET

http://www.albahari.com/threading/

Tip! - Keyboard shortcuts

http://www.itscodingtime.com/post/Visual-Studio-2010-Keyboard-Mouse-Shortcuts.aspx

Resources

LINQ to SQL vs LINQ to Entities http://stackoverflow.com/questions/2443836/what-is-the-di

ffernce-between-linq-to-entities-linq-to-sql-and-linq-to-data

http://www.ssw.com.au/ssw/Standards/Rules/RulesToBetterLINQ.aspx#WhyLINQtoEntitiesNotSQL

Resources - N-Tier apps

.NET C# Visual Studio 2010 LINQ Databinding UX (Usability) Winforms – Best practices N-Tier applications Deployment – Clickonce Security Web services WCF Threading

Part 1 - Review

Sign up on http://www.aspnet4.de/ Yes its german! But free ASP.NET 4 hosting with SQL Server backend Use http://translate.google.com/

ASP.NET Quick hit videos http://www.asp.net/learn/aspnet-4-quick-hit-videos/

Part 2 – ASP.NET The web!!

3 things…

PeterGfader@ssw.com.au

http://peitor.blogspot.com

twitter.com/peitor

Thank You!

Gateway Court Suite 10 81 - 91 Military Road Neutral Bay, Sydney NSW 2089 AUSTRALIA

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Phone: + 61 2 9953 3000 Fax: + 61 2 9953 3105

info@ssw.com.auwww.ssw.com.au

Web services, WCF services and Multi Threading with Windows Forms

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