Superior ways to a better UI

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Developing Windows and Web Applications using
Visual Studio.NET
Presented by Adam Cogan
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Admin Stuff

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

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Session 3 Threading

• Agenda
• What is Threading?
• Application.DoEvents ()
• Thread.Start ()
• The One Golden Rule
• Delegate.BeginInvoke()
• Generate custom events
• Delegates
• Callbacks
• Locking / Monitor.Enter
• Threadpool

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Session 3 Threading
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What is Threading?
Running
Sleeping
Sleeping
Running
Running

• Threading is an illusion.
• E.g. searching file system while waiting for web
  site to load
• Threading is not the perfect solution for
  everything, and we should only use it where
  necessary.
• Restrict your self to a UI thread, and a few
  worker threads.

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What is Threading?

• Threading allows several tasks to run
  simultaneously
• Two major uses
• Responsive UI
• e.g. work with results as they come back
• Optimizing backend processes
• e.g. multiple search engines at once

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What is Threading?

• Responsive UI

Worker Thread
UI Thread
Start
Start
Execute
Update UI
Done
Done
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What is Threading?

• BAD Optimizing backend processes (Scenario)
• e.g. no threading have to wait for results
  for first site before calling second

SearchGoogle()
FetchData()
Fetch
SearchGoogle()
Return
SearchYahoo()
SearchYahoo()
Fetch
Merge
Return
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What is Threading?

• GOOD Optimizing backend processes (Solution)

Worker 1
SearchGoogle()
Return
FetchData
Worker 2
Merge
SearchYahoo()
Done
Return
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How do I use threading?

• 3 Ways
• Application.DoEvents()
• Thread.Start()
• Delegate.BeginInvoke(),ISynchronizeInvoke,IAsync
  Result

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Application.DoEvents()
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Application.DoEvents()

• The UI was partially more responsive
• Still a blocking call
• Still only allows only one worker process to
  execute at a time
• UI updates are tightly bound (worker code is
  directly tied to progress bar cant
  componentise search logic)

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Application.DoEvents()

• Works (but not a great solution)

DoWork()
UI
Start
Start
Execute
Update UI
Done
Done
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Application.DoEvents()

• Not appropriate
• Ideal scenario is

Worker 1
SearchGoogle()
Return
FetchData
Worker 2
Merge
SearchYahoo()
Done
Return
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Thread.Start()
Use a ThreadStart delegate to specify the program
code executed by a thread.
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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
• There is no real way of knowing when the thread
  has finished cant return a status code saying
  Im finished!
• No way of telling when an exception is thrown
• Bad to check the status of the thread

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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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Thread.Start()

• Not appropriate
• Ideal scenario is

Worker 1
SearchGoogle()
Return
FetchData
Worker 2
Merge
SearchYahoo()
Done
Return
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• The One Golden Rule

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The One Golden Rule

• The One Golden Rule
• Windows forms controls must only be accessed from
  the UI thread

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Delegate.BeginInvoke()

• 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.

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Delegate.BeginInvoke()

• The UI was completely responsive
• UI updates are no longer tightly bound (event
  based)
• We know exactly when the call has finished (with
  a callback object)

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Delegate.BeginInvoke()

• Perfect solution

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

• Perfect solution

Worker 1
SearchGoogle()
Return
FetchData
Worker 2
Merge
SearchYahoo()
Done
Return
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Locking / Monitor.Enter

• If you are going to read/write from/to an object
  when using multiple threads, lock the object
  first using lock (obj)
• E.g. reading contact details into a form

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• ManagedThreadPool

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ManagedThreadPool

• What is a Thread Pool?

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• Code Sample
• Implementing ManagedThreadPool

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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 3 Threading

• Summary
• What is Threading?
• Application.DoEvents ()
• Thread.Start ()
• The One Golden Rule
• Delegate.BeginInvoke()
• Generate custom events
• Delegates
• Callbacks
• Locking / Monitor.Enter
• Threadpool

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2 things
AdamCogan_at_ssw.com.au
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Thank You!
ASP.NET is Cool