Deep Dive into Futures and the Parallel Programming Library

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Deep  Dive  into    Futures  and  the  PPLJim  McKeeth  Lead  World  Wide  Developer  Evangelist  /  Engineer  [email protected]  @JimMcKeeth  Tuesday,  the  10rd  February,  2015

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Windows  Mac  OS  X  Android  iOS  RAD  Studio  Appmethod  Object  Pascal  C++

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framework  on  all  4  platforms  while  RAD  Studio,  Delphi  and  C++Builder  also  support  VCL  on  Windows.  Contact  sales  with  any  questions!OP

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The  Parallel  Programming  Library  (PPL)

• Part  of  the  Run-­‐Time  Library  (RTL)  in  System.Threading  • Self-­‐tuning  thread  pool  (based  on  CPU  and  Load)  • Support  for:  • Parallel  For  Loops  • Tasks  -­‐  Units  of  work  • Custom  Thread  Pools  • Futures  -­‐  Async  values

⬅ (Last  week)  ⬅ Part  1  ⬅ Part  2  ⬅ Part  3

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Last  Week’s  Skill  Sprint

• Parallel  For  Loops  • TInterlocked.Increment  • TThread.Queue  • TThread.Synchronize    • For  more  information:  http://delphi.org/?p=1886  

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5 Tasks - Asynchronous Units of Work

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The  TTask  Class  for  Asynchronous  Work  

• A  Task  is  a  unit  of  work  to  be  done  • Not  specific  to  an  individual  thread  • Implements  ITask  with  Start,  Wait,  Cancel  and  Status  • Statuses:  Created,  WaitingToRun,  Running,  Completed,  WaitingForChildren,  Canceled,  Exception  

• Provides  WaitForAll  and  WaitForAny  methods

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WaitForAll  Task  Syntaxvar        tasks:  array  of  ITask;    begin        SetLength  (tasks,  2);            tasks[0]  :=  TTask.Create  (procedure  ()  begin  {Long  running  work}  end);    

   tasks[1]  :=  TTask.Create  (procedure  ()  begin            {  Other  long  running  work  }        end);      tasks[0].Start;        tasks[1].Start;          TTask.WaitForAll(tasks);  //  Blocks  until  completion  end;

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WaitForAll  Task  Syntax{      _di_ITask  tasks[2];            tasks[0]  =  TTask::Create(_di_TProc(new  TCppTask(3000,  Label1)));        tasks[1]  =  TTask::Create(_di_TProc(new  TCppTask(5000,  Label1)));  

     tasks[0]-­‐>Start();        tasks[1]-­‐>Start();            TTask::WaitForAll(tasks,(sizeof(tasks)/sizeof(tasks[0])-­‐1));        ShowMessage("All  done!");  }

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9 Customizing the Thread Pool

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Construct  a  New  Thread  Pool

• Construct  new  TTheadPool  • Customize  Min  &  Max  worker  threads  

• Pass  as  last  optional  parameter  to  Parallel  For,  Task  or  Future  

• Generally  better  off  using  default  thread  pool10

var      FPool  :  TThreadPool;  

//…  

if  FPool  =  nil  then  begin      FPool  :=  TThreadPool.Create;      FPool.SetMaxWorkerThreads(10);  end;  

//…  Use  FPool

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Customizing  the  Thread  Pool

• Customizing  the  default  is  discouraged:  TThreadPool.Default    • SetMaxWorkerThreads(Value:  Integer):  Boolean;  

• Returns  false  if  attempting  to  set  a  value  smaller  than  the  number  of  processors.  Setting  this  value  too  high  can  lead  problems  with  other  libraries  and  processes.  If  too  many  threads  execute  at  the  same  time,  task/thread  switching  overhead  can  become  restrictive.  

• SetMinWorkerThreads(Value:  Integer):  Boolean;  • Returns  false  if  attempting  to  set  a  value  <  0  or  >  MaxWorkerThreads.  The  actual  number  of  pool  threads  could  be  less  than  this  value  depending  on  actual  demand.  Setting  this  to  too  few  threads  could  be  less  than  optimal  resource  utilization.  

• property  MaxWorkerThreads:  Integer  • property  MinWorkerThreads:  Integer

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12 Futures - Calculating Values Asynchronously

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Futures  -­‐  Calculating  Values  Asynchronously

• Future:  Essentially  a  Task  that  returns  a  result  value  • A  future  is  to  a  task  as  a  function  is  to  a  procedure  • Future  is  defined  with  Generic  Type  of  the  result  • Calculates  result  in  the  background  asynchronously  • Will  block  on  read  if  not  finished  • Special  instructions  to  enable  for  C++  (see  download)

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Future  Syntax

var        FutureString:  IFuture<string>;  //  .  .  .      FutureString  :=  TTask.Future<string>(          function:string          begin              Result  :=  DoRESTCall(editArtist.Text);          end);  //  .  .  .      ResultsMemo.Text  :=  FutureString.Value;

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DEMONSTRATIONTasks  and  Futures

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Background  by  Tdvance  used  under  CC-­‐BY-­‐SA  2.5  Font  from  http://www.dafont.com/back-­‐to-­‐the-­‐future.font  

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Review:  Futures  and  the  PPL

• Uses  System.Threading  unit  • Self-­‐tuning  thread  pool  (based  on  CPU  and  Load)  • Tasks  are  asynchronous  units  of  work  • Futures  allow  asynchronous  value  calculation  • Customizable  Thread  Pools

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PPL  Resources

• Samples  – C:\Users\Public\Documents\Embarcadero\Studio\15.0\Samples\Object  Pascal\RTL\Parallel  Library  – C:\Users\Public\Documents\Embarcadero\Studio\15.0\Samples\CPP\RTL\Parallel  Library  

• DocWiki  Overview  – http://docwiki.embarcadero.com/RADStudio/en/Using_the_Parallel_Programming_Library    

• Blog  Posts  – CodeRage  9  Video  http://dannywind.nl/delphi/coderage9/    – Stephen  Ball’s  series  http://delphiaball.co.uk/tag/parallel-­‐programming/    – Malcolm  Groves’  series  http://www.malcolmgroves.com/blog/?cat=109    – Examples,  links  and  more:  http://delphi.org/?p=1914  (Including  the  C++  Lambda  links)

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Next  Time….

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