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Parallel Programming Paradigms

MultithreadingTask level parallelism

ByApex TG India Pvt Ltdhttp://www.apextgi.in

http://www.apextgi.in/

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Serial Vs. Parallel

QPlease

COUNTER

COUNTER 1

COUNTER 2

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Single and Multithreaded Processes

Single-threaded Process

Single instruction stream Multiple instruction stream

Multiplethreaded ProcessThreads of

Execution

CommonAddress Space

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OS:Multi-Processing, Multi-Threaded

Application

Application Application

Application

CPU

Better Response Times in Multiple Application Environments

Higher Throughput for Parallelizeable Applications

CPUCPU

CPU CPU CPU

Threaded Libraries, Multi-threaded I/OThreaded Libraries, Multi-threaded I/O

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Multi-threading, continued...Multi-threaded OS enables parallel, scalable I/O

Application

CPU CPU CPU

Application

Application

OS KernelMultiple, independent I/O requests can be satisfied simultaneously because all the major disk, tape, and network drivers have been multi-threaded, allowing any given driver to run on multiple CPUs simultaneously.

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Shared memory

segments, pipes, open

files or mmapd

files

Shared memory

segments, pipes, open

files or mmapd

files

Basic Process Model

DATADATA

STACK

TEXTTEXT

DATADATA

STACK

TEXTTEXT

processesprocessesShared Memory

maintained by kernelShared Memory

maintained by kernel processesprocesses

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What are Threads?

Thread is a piece of code that can execute in concurrence with other threads.

It is a schedule entity on a processor

Local stateGlobal/ shared statePCHard/Software Context

RegistersRegisters

HardwareContext

Status WordStatus Word

Program CounterProgram Counter

Running Thread Object

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Threaded Process Model

THREAD STACK

THREAD STACK

THREAD DATA

THREAD DATA

THREAD TEXT

THREAD TEXT

SHARED MEMORY

SHARED MEMORY

Threads within a process Independent executables All threads are parts of a process hence communication easier and simpler.

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Code-GranularityCode ItemLarge grain(task level)Program

Medium grain(control level)Function (thread)

Fine grain(data level)Loop

Very fine grain(multiple issue)With hardware

Code-GranularityCode ItemLarge grain(task level)Program

Medium grain(control level)Function (thread)

Fine grain(data level)Loop

Very fine grain(multiple issue)With hardware

Levels of ParallelismLevels of Parallelism

Task i-lTask i-l Task iTask i Task i+1Task i+1

func1 ( ){........}

func1 ( ){........}

func2 ( ){........}

func2 ( ){........}

func3 ( ){........}

func3 ( ){........}

a ( 0 ) =..b ( 0 ) =..

a ( 0 ) =..b ( 0 ) =..

a ( 1 )=..b ( 1 )=..

a ( 1 )=..b ( 1 )=..

a ( 2 )=..b ( 2 )=..

a ( 2 )=..b ( 2 )=..

++ xx LoadLoad

Task Control Data Multiple Issue

Task Control Data Multiple Issue

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Java

Multithreading in Java

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Java - An Introduction

Java - The new programming language from Sun Microsystems

Java -Allows anyone to publish a web page with Java code in it

Java - CPU Independent language Created for consumer electronics Java - James , Arthur Van , and others Java -The name that survived a patent search Oak -The predecessor of Java Java is C++ -- ++

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Object Oriented Languages -A comparison

Feature C++ ObjectiveC

Ada Java

Encapsulation Yes Yes Yes YesInheritance Yes Yes No YesMultiple Inherit. Yes Yes No NoPolymorphism Yes Yes Yes YesBinding (Early or Late) Both Both Early LateConcurrency Poor Poor Difficult YesGarbage Collection No Yes No YesGenericity Yes No Yes NoClass Libraries Yes Yes Limited Yes

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Sun defines Java as:

Simple and PowerfulSimple and Powerful SafeSafe Object OrientedObject Oriented RobustRobust Architecture Neutral and PortableArchitecture Neutral and Portable Interpreted and High PerformanceInterpreted and High Performance Threaded Threaded DynamicDynamic

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Java Integrates Power of Compiled Languages

and Flexibility of Interpreted Languages

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Threads

Java has built in thread support for Multithreading Synchronization Thread Scheduling Inter-Thread Communication:

currentThread start setPriorityyield run getPrioritysleep stop suspend

resume Java Garbage Collector is a low-priority thread

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Ways of Multithreading in Java Create a class that extends the Thread class Create a class that implements the Runnable interface 1st Method: Extending the Thread class class MyThread extends Thread {

public void run() { // thread body of execution } } Creating thread: MyThread thr1 = new MyThread(); Start Execution: thr1.start();

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2nd method: Threads by implementing Runnable interface

class ClassName implements Runnable{ ..... public void run() { // thread body of execution }} Creating Object: ClassName myObject = new ClassName(); Creating Thread Object: Thread thr1 = new Thread( myObject ); Start Execution: thr1.start();

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Thread Class Members...public class java.lang.Thread extends java.lang.Object implements java.lang.Runnable {// Fieldspublic final static int MAX_PRIORITY;public final static int MIN_PRIORITY;public final static int NORM_PRIORITY;// Constructorspublic Thread();public Thread(Runnable target);public Thread(Runnable target, String name);public Thread(String name);public Thread(ThreadGroup group, Runnable target);public Thread(ThreadGroup group, Runnable target, String name);public Thread(ThreadGroup group, String name);// Methodspublic static int activeCount();public void checkAccess();public int countStackFrames();public static Thread currentThread();public void destroy();public static void dumpStack();public static int enumerate(Thread tarray[]);public final String getName();

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...Thread Class Members.public final int getPriority(); // 1 to 10 priority-pre-emption at mid.public final ThreadGroup getThreadGroup();public void interrupt();public static boolean interrupted();public final boolean isAlive();public final boolean isDaemon();public boolean isInterrupted();public final void join();public final void join(long millis);public final void join(long millis, int nanos);public final void resume();public void run();public final void setDaemon(boolean on);public final void setName(String name);public final void setPriority(int newPriority);public static void sleep(long millis);public static void sleep(long millis, int nanos);public void start();public final void stop();public final void stop(Throwable obj);public final void suspend();public String toString();public static void yield();}

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Manipulation of Current Thread// CurrentThreadDemo.javaclass CurrentThreadDemo { public static void main(String arg[]) { Thread ct = Thread.currentThread(); ct.setName( "My Thread" ); System.out.println("Current Thread : "+ct); try { for(int i=5; i>0; i--) { System.out.println(" " + i); Thread.sleep(1000); } } catch(InterruptedException e) { System.out.println("Interrupted."); } }}Run:Current Thread : Thread[My Thread,5,main] 5 4 3 2 1

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Creating new Thread...

// ThreadDemo.javaclass ThreadDemo implements Runnable{ ThreadDemo() { Thread ct = Thread.currentThread(); System.out.println("Current Thread : "+ct); Thread t = new Thread(this,"Demo Thread"); t.start(); try { Thread.sleep(3000); } catch(InterruptedException e) { System.out.println("Interrupted."); } System.out.println("Exiting main thread."); }

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...Creating new Thread.public void run() { try { for(int i=5; i>0; i--) { System.out.println(" " + i); Thread.sleep(1000); } } catch(InterruptedException e) { System.out.println("Child interrupted."); } System.out.println("Exiting child thread."); } public static void main(String args[]) { new ThreadDemo(); }}Run:Current Thread : Thread[main,5,main] 5 4 3Exiting main thread. 2 1Exiting child thread.

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Thread Priority...// HiLoPri.javaclass Clicker implements Runnable { int click = 0; private Thread t; private boolean running = true; public Clicker(int p) { t = new Thread(this); t.setPriority(p); } public void run() { while(running) click++; } public void start() { t.start(); } public void stop() { running = false; }}

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...Thread Priorityclass HiLoPri{ public static void main(String args[]) { Thread.currentThread().setPriority(Thread.MAX_PRIORITY); Clicker Hi = new Clicker(Thread.NORM_PRIORITY+2); Clicker Lo = new Clicker(Thread.NORM_PRIORITY-2); Lo.start(); Hi.start(); try { Thread.sleep(10000); } catch (Exception e) { } Lo.stop(); Hi.stop(); System.out.println(Lo.click + " vs. " + Hi.click); }}Run1: (on Solaris)0 vs. 956228Run2: (Window 95)304300 vs. 4066666

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The Java monitor model

Method 1

Method 2

Block 1Key

Threads

Monitor (synchronised) solves race-condition problem

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Parallel Programming ParadigmsSerial Vs. ParallelSingle and Multithreaded ProcessesPowerPoint PresentationSlide 5Basic Process ModelWhat are Threads?Threaded Process ModelSlide 9JavaJava - An IntroductionObject Oriented Languages -A comparisonSun defines Java as:ThreadsWays of Multithreading in Java2nd method: Threads by implementing Runnable interfaceThread Class Members......Thread Class Members.Manipulation of Current ThreadCreating new Thread......Creating new Thread.Thread Priority......Thread PriorityThe Java monitor modelSlide 26