.NET Multithreading and File I/O

.NET Multithreading and File I/O

• 1.
  Mul$threaded  and  Async   Programming  in  C#  +  File  IO   Jussi  Pohjolainen   Tampere  University  of  Applied  Sciences  
• 2.
  Delegates   •  You  can  invoke  a  method  (determined  by   run$me)  from  a  delegate   public delegate int SomeMethod(int x, int y); Console.WriteLine("Thread is " + Thread.CurrentThread.ManagedThreadId); SomeMethod a = new SomeMethod(Sum); Console.WriteLine( a.Invoke(5,5) ); •  It's  possible  to  make  the  invoke  in  separate  thread!
• 3.
  Asynchronous  Delegate   • By  using  the  same  delegate,  but  calling   BeginInvoke,  the  method  is  done  in  separate   thread   –  public IAsyncResult BeginInvoke(parameters.., AsyncCallback cb, object state) –  public returnType EndInvoke(IAsyncResult result) •  If  the  method  returns  something,  use   EndInvoke  to  get  the  return  value.
• 4.
  using System; using System.Threading; publicdelegate int SomeMethod(int x, int y); class MyMain { public static void Main() { SomeMethod a = new SomeMethod(Sum); Console.WriteLine("Firing Asynchronous method"); // IAsyncResult - Represents the status of an asynchronous operation. IAsyncResult iftAR = a.BeginInvoke(5, 5, null, null); Console.WriteLine("Doing some work here!"); int answer = a.EndInvoke(iftAR); Console.WriteLine(answer); } public static int Sum(int x, int y) { Console.WriteLine("Thread is " + Thread.CurrentThread.ManagedThreadId); Thread.Sleep(2000); return x + y; } }
• 5.
  Synchronizing  Calling  Thread   •  If  we  look  at  this  more  closely   –  Console.WriteLine("Firing Asynchronous method"); –  IAsyncResult iftAR = a.BeginInvoke(5, 5, null, null); –  Console.WriteLine("Doing some work here!"); –  // We are waiting here! –  int answer = a.EndInvoke(iftAR); •  We  realize  that  the  a.EndInvoke  waits  un$l  the   "calcula$on"  is  done
• 6.
  using System; using System.Threading; publicdelegate int SomeMethod(int x, int y); class MyMain { public static void Main() { SomeMethod a = new SomeMethod(Sum); Console.WriteLine("Firing Asynchronous method"); IAsyncResult iftAR = a.BeginInvoke(5, 5, null, null); while(!iftAR.IsCompleted) { Console.WriteLine("Doing some work here!"); } int answer = a.EndInvoke(iftAR); Console.WriteLine(answer); } public static int Sum(int x, int y) { Console.WriteLine("Thread is " + Thread.CurrentThread.ManagedThreadId); Thread.Sleep(2000); return x + y; } }
• 7.
  Rid  of  Polling   •  Instead  of  polling,  it  would  be  a  good  idea  to   have  a  secondary  thread  to  inform  the  calling   thread  when  the  task  is  finished.  
• 8.
  using System; using System.Threading; publicdelegate int SomeMethod(int x, int y); class MyMain { private static bool done = false; public static void Main() { SomeMethod a = new SomeMethod(Sum); Console.WriteLine("Firing Asynchronous method"); IAsyncResult iftAR = a.BeginInvoke(5, 5, new AsyncCallback(Done), null); while(!done) { Console.WriteLine("Doing some work here!"); } int answer = a.EndInvoke(iftAR); Console.WriteLine(answer); } public static int Sum(int x, int y) { Console.WriteLine("Thread is " + Thread.CurrentThread.ManagedThreadId); Thread.Sleep(2000); return x + y; } public static void Done(IAsyncResult result) { done = true; } }
• 9.
  using System; using System.Threading; usingSystem.Runtime.Remoting.Messaging; public delegate int SomeMethod(int x, int y); class MyMain { private static bool done = false; public static void Main() { SomeMethod a = new SomeMethod(Sum); Console.WriteLine("Firing Asynchronous method"); // Passing custom state data a.BeginInvoke(5, 5, new AsyncCallback(Done), "Message Sending!"); while(!done) { Console.WriteLine("Doing some work here!"); } } public static void Done(IAsyncResult iftAR) { // IAsyncResult is interface, actual object is AsyncResult AsyncResult ar = (AsyncResult) iftAR; // AsyncResult holds the delegate SomeMethod sm = (SomeMethod) ar.AsyncDelegate; // Make the call int answer = sm.EndInvoke(iftAR); Console.WriteLine(answer); // Also print the message! string msg = (string) iftAR.AsyncState; Console.WriteLine(msg); done = true; } }
• 10.
  THREADING  NAMESPACE  
• 11.
  Threading  Namespace   • Threading  namespace  provides  lot  of  classes   for  crea$ng  threads   –  Thread  –  Main  class  for  crea$ng  a  thread   –  ThreadStart  –  delegate  used  to  specify  which   method  is  run  under  a  thread   –  Timer  –  Mechanism  for  execu$ng  a  method  at   specified  intervals   –  Lot  of  locking  mechanisms    
• 12.
  System.Threading.Thread  Class   • Some  sta$c  members   –  CurrentThread  –  get  the  current  thread   –  Sleep()  –  Suspend  current  thread   •  Some  AZributes   –  IsAlive   –  Name   –  Priority   •   Some  Methods   –  Abort()   –  Join()   –  Start()   –  …  
• 13.
  Ge]ng  Informa$on  About  the  Current   Thread   using System; using System.Threading; class MyMain { public static void Main() { Thread.CurrentThread.Name = "My THREAD!"; Console.WriteLine("Name: "); Console.WriteLine(Thread.CurrentThread.Name); Console.WriteLine("IsAlive: "); Console.WriteLine(Thread.CurrentThread.IsAlive); Console.WriteLine("Priority: "); Console.WriteLine(Thread.CurrentThread.Priority); Console.WriteLine("ThreadState: "); Console.WriteLine(Thread.CurrentThread.ThreadState); } }
• 14.
  using System; using System.Threading; publicclass Simple { public static void DoThis() { int i=0; while (true) { Console.WriteLine("Running in its own thread. " + i); Thread.Sleep(500); i++; } } public static void Main() { Thread aThread = new Thread(new ThreadStart(DoThis)); aThread.Start(); Thread bThread = new Thread(new ThreadStart(DoThis)); bThread.Start(); } }
• 15.
  using System; using System.Threading; publicclass Simple { public static void DoThis(object data) { int i=0; while (i < (int) data) { Console.WriteLine("Running in its own thread. " + i); Thread.Sleep(500); i++; } } public static void Main() { Thread aThread = new Thread(new ParameterizedThreadStart(DoThis)); aThread.Start(10); } }
• 16.
  About  Locking   • When  mul$ple  threads  access  same   informa$on  -­‐>  unstable  data   •  Example:  one  bank  account,  two  withdrawals   at  the  same  $me   –  1)  is  there  enough  money?   –  2)  if  true,  withdraw   •  We  have  a  problem  if  these  steps  are  done  at   the  same  $me:  1,1,2,2  
• 17.
  Solu$on   •  One  solu$on  is  to  use  lock  keyword   •  If  on  thread  holds  a  lock,  others  wait   •  lock  is  any  object   •  Usage  lock(object){    }  
• 18.
  Timers   using System; usingSystem.Threading; class Hello { public static void DoThis(object data) { Console.WriteLine("Hello!"); } public static void Main() { TimerCallback timeCB = new TimerCallback(DoThis); Timer t = new Timer(timeCB, // call back delegate object null, // Any info to the method 0, // Time before first invocation 1000); // Interval Console.ReadLine(); } }
• 19.
  Background  Worker   • hZp://msdn.microsog.com/en-­‐us/library/cc221403(v=vs.95).aspx   private void Button_Click_2(object sender, RoutedEventArgs e) { BackgroundWorker bw = new BackgroundWorker(); bw.DoWork += DoTheWork; bw.RunWorkerCompleted += Complete; bw.RunWorkerAsync(); } public void DoTheWork(object sender, DoWorkEventArgs e) { Thread.Sleep(500); } public void Complete(object sender, RunWorkerCompletedEventArgs e) { Title = "Hello"; }
• 20.
  GUI  AND  THREADING  
• 21.
  Access  UI  from  Thread   •  If  a  secondary  thread  aZempt  to  access  a  control  it  did  not   create  =>  run$me  error!     private void Button_Click_2(object sender, RoutedEventArgs e) { Thread thread = new Thread(new ThreadStart(ModifyTitle)); thread.Start(); } // Runtime Exception! public void ModifyTitle() { Title = "Hello World"; }
• 22.
  Dispatcher  Class   • Dispatcher  class  allows  you  to  modify  UI  from   secondary  thread   •  Read   –  hZp://msdn.microsog.com/en-­‐us/magazine/ cc163328.aspx  
• 23.
  private void Button_Click_2(objectsender, RoutedEventArgs e) { Thread t = new Thread(new ThreadStart(ModifyTitle)); t.Start(); } public void ModifyTitle() { Thread.Sleep(1000); // Change title to "Hello" Dispatcher.Invoke(new Action(ChangeTitle)); Thread.Sleep(1000); // Lambda Dispatcher.Invoke(() => this.Title = "World"); Thread.Sleep(1000); Dispatcher.Invoke(() => this.Title = ""); string newTitle = "Hello World!"; for (int i = 0; i < newTitle.Length; i++) { Thread.Sleep(100); Dispatcher.Invoke(() => this.Title += newTitle[i]); } } public void ChangeTitle() { this.Title = "Hello"; }
• 24.
  Upda$ng  UI  and  Timer   •  Timer  calls  certain  method  in  interval   •  When  using  Threading.Timer  the  task  is  in   different  thread   –  Use  Dispatcher.Invoke  to  manipulate  the  UI  thread   •  When  using   Windows.Threading.DispatcherTimer,  the  task  in   in  UI  thread   –  If  this  performs  a  $me  consuming  task,  the  UI  will   freeze    
• 25.
  ASYNC  CALLS  
• 26.
  Aync  Calls  Under  .NET  4.5   •  Two  new  keywords  to  simplify  threading  even   more   –  async  and  await   •  Compiler  will  generate  lot  of  code  when  using   these  keywords   •  async   –  Method  should  be  called  in  an  asynchronous  manner   automa$cally   •  await   –  Pause  current  thread  un$l  task  is  complete  
• 27.
  async  and  await   •  In  .NET  4.5,  new  keywords:  async  and  await   •  Simplifies  threading,  generates  a  lot  of  code!   •  See:   –  hZp://blogs.msdn.com/b/pfxteam/archive/ 2012/04/12/10293335.aspx  
• 28.
  namespace WpfApplication2 { /// <summary> /// Interaction logic for MainWindow.xaml /// </summary> public partial class MainWindow : Window { public MainWindow() { InitializeComponent(); } private async void Button_Click_1(object sender, RoutedEventArgs e) { WebClient wb = new WebClient(); Task<string> result = wb.DownloadStringTaskAsync(new Uri("http://www.tamk.fi/")); string r = await result; Contents.Text = r; } } }
• 29.
  FILE  I/O  
• 30.
  Overview   •  System.IO  namespace  provides  number  of  classes   for  reading  and  wri$ng   •  Store  and  retrieve  primi$ve  types   –  BinaryReader,  BinaryWriter   •  Store  and  retrieve  text   –  StreamReader,  StreamWriter   •  Buffered  reading   –  BufferedStream   •  Helper  classes  like  File  (sta$c),  FileInfo  (object   reference  
• 31.
  Reading  and  Wri$ng  Text   •  StreamWriter  and  StreamReader  use  useful   when  need  for  read  or  write  text   •  By  default:  Unicode   –  Can  be  changed:  pass  System.TextEncoding  object   reference   •  Methods   –  Write(),  WriteLine()  
• 32.
  Wri$ng   class SaveText { public static void Main() { StreamWriter writer = File.CreateText("./textfile.txt"); // Nothing happens! Why? writer.WriteLine("Hello World!"); writer.WriteLine("Hello World!"); } }
• 33.
  Wri$ng:  Flush  it!   using System; using System.IO; class SaveText { public static void Main() { StreamWriter writer = File.CreateText("./textfile.txt"); writer.WriteLine("Hello World!"); writer.WriteLine("Hello World!"); writer.Flush(); } }
• 34.
  Wri$ng:  Stream  should  be  closed!   using System; using System.IO; class SaveText { public static void Main() { StreamWriter writer = File.CreateText("./textfile.txt"); writer.WriteLine("Hello World!"); writer.WriteLine("Hello World!"); writer.Flush(); writer.Close(); } }
• 35.
  Wri$ng:  Flushing  is  done  when   closing!   using System; using System.IO; class SaveText { public static void Main() { StreamWriter writer = File.CreateText("./textfile.txt"); writer.WriteLine("Hello World!"); writer.WriteLine("Hello World!"); writer.Close(); } }
• 36.
  Wri$ng:  using   usingSystem; using System.IO; class ReadText { public static void Main() { using( StreamWriter writer = File.CreateText("./textfile.txt") ) { writer.WriteLine("Hello World!"); writer.WriteLine("Hello World!"); } } }
• 37.
  Reading  Text   usingSystem; using System.IO; class ReadText { public static void Main() { using( StreamReader reader = File.OpenText("./textfile.txt") ) { string input = null; while((input = reader.ReadLine()) != null) { Console.WriteLine(input); } } } }
• 38.
  Reading  and  Wri$ng  Binary   using System; using System.IO; class ReadBinary { public static void Main() { using( BinaryWriter writer = new BinaryWriter( File.OpenWrite("./test.dat") ) ) { writer.Write(2.2); } using( BinaryReader reader = new BinaryReader( File.OpenRead("./test.dat") ) ) { Console.WriteLine(reader.ReadDouble()); } } }
• 39.
  Watching  Files   • Monitor  or  watch  files  using   FileSystemWatcher  class   •  Really  easy  to  implement   –  Which  folder  are  we  looking?   –  Set  up  things  to  listen   –  Add  Filters   –  Add  Event  Handlers   –  Start  listening  
• 40.
  Example   using System; usingSystem.IO; class Watcher { public static void Main() { FileSystemWatcher watcher = new FileSystemWatcher(); watcher.Path = "/Users/pohjus/Desktop/tuhoa/"; watcher.NotifyFilter = NotifyFilters.LastWrite | NotifyFilters.FileName; watcher.Filter = "*.txt"; watcher.Changed += (object source, FileSystemEventArgs e) => Console.Write("Changed"); watcher.Deleted += (object source, FileSystemEventArgs e) => Console.Write("Deleted"); watcher.EnableRaisingEvents = true; Console.Read(); } }
• 41.
  Serializable   •  Serializa$on?  Store  an  state  of  the  object  into   stream!   •  Example:  Store  app  preferences  into  a  file.   Preference  informa$on  are  stored  in  object.   •  How?  Mark  a  class  as  Serializable  and  use   classes  to  store  and  open  the  object   •  You  can  save  the  object  as  binary  or  xml  (use   XMLSerializer  -­‐  class)  
• 42.
  using  System;   using  System.IO;   using  System.Run$me.Serializa$on.FormaZers.Binary;     [Serializable]   class  Person   {    public  string  Name  {  get;  set;  }    public  int  Age  {  get;  set;  }   }   class  SerializableExample   {    public  sta$c  void  Main()    {      Person  jack  =  new  Person()  {  Name  =  "Jack",  Age  =  20  };        //  Let's  save  jack  as  binary      BinaryFormaZer  binFormat  =  new  BinaryFormaZer();        //  And  in  which  file?      using(FileStream  fs  =  new  FileStream("person.dat",  FileMode.Create))      {        //  Let's  do  it!        binFormat.Serialize(fs,  jack);      }    }   }    
• 43.
  using  System;   using  System.IO;   using  System.Run$me.Serializa$on.FormaZers.Binary;     [Serializable]   class  Person   {    public  string  Name  {  get;  set;  }    public  int  Age  {  get;  set;  }   }     class  SerializableExample   {    public  sta$c  void  Main()    {      BinaryFormaZer  binFormat  =  new  BinaryFormaZer();        //  Deserialize!      using(FileStream  fs  =  new  FileStream("person.dat",  FileMode.Open))      {        Person  jack2  =  (Person)  binFormat.Deserialize(fs);        Console.WriteLine(jack2.Name);        Console.WriteLine(jack2.Age);      }    }   }  
• 44.
  ABOUT  WIN  DESKTOP  APPS  
• 45.
  WPF   •  Windows  Presenta$on  Founda$on  (or  WPF)  is   a  computer-­‐sogware  graphical  subsystem  for   rendering  user  interfaces  in  Windows-­‐based   applica$ons   •  WPF  employs  XAML,  an  XML-­‐based  language,   to  define  and  link  various  UI  elements   •  See   –  hZp://msdn.microsog.com/en-­‐us/library/ ms752299.aspx