Programming with Skeletons: Skandium

Patrizio Dazzi (ISTI-CNR)Distributed systems: paradigms and models

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How to contact mePatrizio DazziMail: patrizio.dazzi@isti.cnr.itPhone: +39 050 315 3074Web: http://hpc.isti.cnr.it/~dazzi

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What will we see ?

Frameworks for Programming in Parallel with Skeletons

Today SkandiumFriday SkeTo

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Today OutlineSkandium framework Overview

Future conceptUsing Skandium SkeletonsSample ApplicationsDemo on my machine

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Framework conceived by Mario LeytonINRIA, FranceUniversity of Chile

Previously implemented in ProActive

Strongly relies on Future - Wait-By-Necessity semantics

Java based framework

Home page: http://skandium.niclabs.cl/

Skandium History

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Traditional control flow

Method A calls Method BA execution is stopped until B ends its execution.... is this always the behavior we need ?NO! let’s see and example

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Example simple sequential computation

A computer C needs statistics about a set S of computersStatistics are computed locally by each computer belonging to SEach statistics requires T secondsTotal time required (T x #S) seconds + (Tcomm(req) x #S) + (Tcomm(answ) x #S)

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Showing the exampleObject A Object B

RMI invocation without Futures

res = B.method();method(){ ... return value;}

Now value is available

value

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FuturesNatively supported by Java from release 5.0

Result Placeholder

Needed to achieve Asynchrony with standard Javawithout callbacks!!!

E.g.Future<Integer> fi1 = methodCall(A);Future<Integer> fi2 = methodCall(B);

Suppose each call requires 3 seconds and youhave 2 cores

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A Future exampleObject A Object B

RMI invocation with Futures

method(){ ... return value;}

put value in the container already sent

res = B.method();empty container

If the res variable is not accessed the computation can continue

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How is it set up in Java ?

Typically used in RMI or RMI-like based communication modelsA Future represents the result of an asynchronous computation. Typically, it defines proper methods

to check if the computation has been completedto wait for its completion, and to retrieve the result of the computation.

From a more theoretical point of view this inter-object synchronization policy is known as wait-by-necessity

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Wait-by-necessity

Asynchronous execution of sequential code

the client waits when it logically needs to

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Skeletons in SkandiumA lot of available SkeletonsWe will focus on a subset:

Task Parallelfarmpipeline

Data Parallelmap

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Additional Entities

StreamsExecute interfaceFuture collections

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Farm in Skandium (1)Elaborations performed by multiple “workers”Each worker computes the same application code on different, independent tasks

Tasks Computed Tasks

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Farm in Skandium (2)

class Farm

Two Constructors

public class Farm<P,R> extends AbstractSkeleton<P,R>public abstract class AbstractSkeleton<P,R> implements Skeleton<P,R>

public Farm(Skeleton<P,R> skeleton)public Farm(Execute<P,R> execute)

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Sample Farm usage (1)

public class Worker implements Execute<Integer, Integer> {

@Override public Integer execute(Integer arg0) throws Exception { Thread.sleep(3000); return new Integer(((int)Math.pow(2, arg0))); }

}

Worker

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Sample Farm usage (2)public class FirstFarm {

public static void main(String[] args) {

Skeleton<Integer, Integer> farm = new Farm<Integer, Integer>(new Worker()); Vector<Future<Integer>> futures = new Vector<Future<Integer>>(); futures.add(farm.input(new Integer(2))); futures.add(farm.input(new Integer(3))); futures.add(farm.input(new Integer(4))); futures.add(farm.input(new Integer(5))); long currentTime = System.currentTimeMillis(); for(Future<Integer> future:futures){ Integer res = null; try { res = future.get(); } catch (InterruptedException e) { e.printStackTrace(); } catch (ExecutionException e) { e.printStackTrace(); } System.out.println(res); } System.out.println("Time Elapsed: "+(System.currentTimeMillis()-currentTime)); System.exit(0); }}

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Sample Farm Usage (2)

Skeleton<Integer, Integer> farm = new Farm<Integer, Integer>(new Worker());

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Map in Skandium (1)Elaborations performed by multiple Processing elements (PEs)Each PE computes the same application code on a fragment of the input data

Data Computed Data

Split Merge

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Map in Skandium (2)

class Map

Two Constructors

public class Map<P,R> extends AbstractSkeleton<P,R> public abstract class AbstractSkeleton<P,R> implements Skeleton<P,R>

public <X,Y> Map(Split<P,X> split, Execute<X,Y> execute, Merge<Y,R> merge)public <X,Y> Map(Split<P,X> split, Skeleton<X,Y> skeleton, Merge<Y,R> merge)

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Sample Map usage (1)

public class CharProcessor implements Execute<Character, Character> {

@Override public Character execute(Character param) throws Exception { char c = param.charValue(); char upC = Character.toUpperCase(c); return new Character(upC); }

}

Computation executed by each processing element

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Sample Map usage (2)public class FirstMap {

public static void main(String[] args) throws Exception { int PARTS = Runtime.getRuntime().availableProcessors()*4; Skeleton<String, String> string = new Map<String, String>( new SplitInterval(), new CharProcessor(), new MergeResults());

long init = System.currentTimeMillis(); Future<String> future = string.input(new String("hello world today I feel good!"));

String result = future.get(); System.out.println((System.currentTimeMillis() - init)+"[ms]: "+result); }}

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Sample Map Usage (2)

Skeleton<String, String> map = new Map<String, String>(new SplitInterval(),new CharProcessor(),new MergeResults());

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Pipeline in Skandium (1)Applications organized in Stages

Each Stage performs a specific computation

Tasks Computed Tasks

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Pipeline in Skandium (2)Class Pipeline

Two Constructors

public class Pipe<P,R> extends AbstractSkeleton<P,R>

public Pipe(Skeleton<P,R> stage1, Skeleton<P,R> stage2)public Pipe(Execute<P,R> stage1,Execute<P,R> stage2)

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Sample Pipeline Usage (1)

public class Incr implements Execute<Integer, Integer> { public Integer execute(Integer arg0) throws Exception { return new Integer(arg0+1); }}

public class Power implements Execute<Integer, Integer> { public Integer execute(Integer arg0) throws Exception {

return arg0*arg0; }}

First Stage

Second Stage

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Sample Pipeline Usage (2)

public static void main(String[] args) throws Exception {

Skeleton<Integer, Integer> pipeline = new Pipe<Integer, Integer>(new Incr(), new Power());

Vector<Future<Integer>> futures = new Vector<Future<Integer>>(); try { futures.add(pipeline.input(new Integer(2))); futures.add(pipeline.input(new Integer(3))); } catch (Exception e1) { e1.printStackTrace(); } for(Future<Integer> future:futures){ Integer res = future.get(); System.out.println(res); } System.exit(0); }

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Sample Pipeline Usage (3)

Skeleton<Integer, String> pipeline = new Pipe<Integer, String>(new Incr(), new StringMaker());

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Compiling a Skandium Application

Sun Java Compiler, version >= 5

Add to the Java CLASSPATH the jar file in dist/lib

Use javac <source code>

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Questions ?

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