YOW Joseph Albahari Asynchronous Functions in C# 5gotocon.com/.../slides/YOW-Joseph-Albahari-Asynchronous-Functions.pdf · SpeakerphoneConcurrency True)Asynchronous)Call) Caller!manages!concurrency!

Asynchrony  in  C#  5  Deep  Dive    

Joe  Albahari  Asynchronized  swimming  Beijing  Olympics  

JOE  ALBAHARI  www.albahari.com  

Asynchronous  Programming  is  the  theme  of  C#  5  (and  VB11)  

…and  Framework  4.5!  

New  keywords!  

(466  new  asynchronous  “TAP”  methods)  

We  need  concurrency.  

But  how?  

Standard  soluPon  =  threading  

Explicit:  new  Thread()...  Implicit:  BackgroundWorker  

Who  enjoys  debugging  mulHthreaded  code?  

“We’re  here  to  help!”  

“Your  call  is  important  to  us.      Please  hold  the  line!”  

“Please  enter  your  phone  number  and  press  #”  

“We’ll  call  you  back”  

Callback  

20  minutes  later…  

ConPnuaPon  

Sync  vs.  Async  Synchronous  call   Asynchronous  call  Caller  WAITS  for  method  to  complete  

Method  returns  immediately  to  caller,  and  executes  callback  (conPnuaPon)  when  complete  

“Blocking”   “Non-­‐blocking”  

Speakerphone  Concurrency   True  Asynchronous  Call  Caller  manages  concurrency   Callee  manages  concurrency  

Caller  spins  up  thread   Callee  may  start  a  thread  

–  and  WAITS  on  that  thread  

No  callback/conPnuaPon  required  

Callback/conPnuaPon  usually  required  

Why  async?  •  Beber  thread  safety  

•  Less  plumbing  code  

•  Can  avoid  blocking  threads  (if  I/O  bound)  –  Which  improves  scalability  –  And  keeps  the  thread  pool  clean  

•  Can  abstract  concurrency  

Framework  1.0:  APM  (IAsyncResult  pabern)  stream.BeginRead(…….)  stream.EndRead(…….)  FAIL!    Requires  therapist    

Framework  2.0:  EAP  webClient.DownloadStringCompleted  +=  ……  webClient.DownloadStringAsync(……..)  FAIL!    Not  composable  

Framework  4.0:  Tasks  

string  GetWebPage  (string  uri)  {      ...      ...  

}  

void  Test()  {      string  html  =  GetWebPage(“...”);      Console.WriteLine  (html);  }  

void  GetWebPageAsync  (  string  uri,  Action<string>  continuation)  

{      ...      ...  

}  

void  Test()  {      GetWebPageAsync(“...”,  Console.WriteLine);  

}  

Task<string>  GetWebPageAsync  (string  uri)  {      ...      ...  }  

Task<TResult>  Result  property  ExcepHon  property  ConHnueWith()  method  

Task<TResult>  is  a  value-­‐added  signaling  construct  

Tasks  deprecate  the  APM  and  REAP!  

Task<string>  GetWebPageAsync  (string  uri)  {      ...      ...  

}  

void  Test()  {      GetWebPageAsync(“...”).ContinueWith  (task  =>          Console.WriteLine  (task.Result));  }  

Task<string>  GetWebPageAsync  (string  uri)  {      ...      ...  

}  

Task  Test()  {      return          GetWebPageAsync(“...”).ContinueWith  (task  =>              Console.WriteLine  (task.Result));  }  

string  GetWebPage  (string  uri)  {      ...      ...  }  

void  Test()  {      for  (int  i  =  0;  i  <  5;  i++)      {          string  html  =  GetWebPage(“...”);          Console.WriteLine  (html);      }  }  

Task<string>  GetWebPageAsync  (string  uri)  {      ...      ...  }  

int  _i  =  0;  void  Test()  {      GetWebPageAsync(“...”).ContinueWith  (task  =>        {          Console.WriteLine  (task.Result);          if  (++_i  <  5)  Test();      });  }  

ConPnuaPons  and  imperaPve  code  don’t  mix!  

That’s  why  we  need  C#  language  support      aka    asynchronous  funcHons  

Demos  •  LINQPad  Demo  •  VS  Project  Demo  

Hooray!  

Framework  4.5:  

APM      353  methods  REAP      38  methods  TAP        466  methods    

The  TAP  deprecates  the  APM  and  REAP  

C#  1   C#  2  • Generics  • Nullable  Types  •  Closures  

C#  3  •  Lambda  Expressions  • Query  comprehensions  •  Extension  methods  

C#  4  • Dynamic  Binding  •  Parallel  Programming  (CLR)  

Parallel  Programming  

Task  Parallel  Library  

PLINQ  

FW  4.0  

Latency  

Async  FuncPons  (C#  5)  

Rx  

vNext  

Concurrency  

ImperaHve   ImperaHve  FuncHonal   FuncHonal  

Thinking  asynchronously  •  Stop  thinking  in  terms  of  threads!  

•  Program  synchronously,  then  await  instead  of  wai:ng  

•  Don’t  block  (await  instead)  

•  Keep  concurrency  fine-­‐grained    &  all  the  way  down!  

Resources  •  CTP:  download  from  MS  (search  “async  CTP”)  

•  MS  Async  CTP  Forum  (search  “async  CTP  forum”)  

•  LINQPad  InteracHve  Async  Tutorial  (click  Download  more  samples  from  LINQPad)