Concorr^encia. A classe Thread (java.lang)

(1)

Concorr^encia

I

_{Concorr^encia em Java}

I

MultiThreading

I

sincronizac~ao

I

interface Runnable

I

grupos de threads

I

exemplos

Rui Camacho Complementos de Programac~ao e Algoritmos { LEIC

Apresentac~ao Java { conceitos Basicos

Java { topicos especcos

A classe Thread

(java.lang)

Os threads s~ao dependentes da plataforma. Correm por quantum de tempo em

Windows e em modo preemptive no Solaris.

Escalonador privilegia as prioridades (entre 0 e 10) mais elevadas. Podem

correr em modo daemon.

I

_{construtores: Thread(String nome), Thread(Runnable obj), ...}

I

_{metodo run() onde existe o codigo do thread}

I

_{metodo start() inicia o thread e termina}

I

_{static sleep(long MiliSegundos) coloca o thread no estado sleep}

I

_{metodo interrupt()}

I

_{metodos suspend() / resume()}

I

_{metodo stop() termina um thread (n~ao e muito usado)}

(2)

Estados de um thread

I

_{ready | pronto a executar quando houver 1 CPU}

I

_{running | em execuc~ao}

I

_{suspended | activavel com chamada a resume()}

I

_{blocked | a espera de uma operac~ao E/S}

I

_{sleeping | sem executar por um perodo pre-determinado}

I

_waiting

I

_{dead | terminou a sua execuc~ao}

Threads

do livro \Java How to Program", Deitel & Deitel

(3)

Threads

{ exemplo simples {

class PrintThread extends Thread f

int sleepTime;

public PrintThread() f

// sleep between 0 and 5 seconds

sleepTime = (int) ( Math.random() * 5000 );

System.out.println( "Name: " + getName() +

"; sleep: " + sleepTime );

g

public void run() f

try f

Thread.sleep( sleepTime );

// put thread to sleep for a random interval

System.out.println(\Dormi durante \+sleepTime+" segundos. Ate ja.");

g

catch (InterruptedException exception) f

System.err.println(exception.toString());

g

System.out.println(getName());

g

exemplo do livro \Java How to Program", Deitel & Deitel

Threads

{ exemplo simples {

public class PrintTest f

// Show multiple threads printing at dierent intervals.

public static void main(String args[])f

PrintThread thread1, thread2, thread3, thread4;

thread1 = new PrintThread();

thread2 = new PrintThread();

thread3 = new PrintThread();

thread4 = new PrintThread();

thread1.start();

thread2.start();

thread3.start();

thread4.start();

g

(4)

Sincronizac~ao

I

_{Uso de monitors (C.A. Hoare)}

I

_{Cada objecto com um metodo synchronized e um monitor}

I

_{O monitor deixa um so thread de cada vez correr um metodo}

synchronized no objecto

I

_{todos os threads que tentam invocar um metodo synchronized}

num objecto locked t^em que esperar

Sincronizac~ao

(cont.)

I

_{quando um metodo synchronized termina o monitor levanta o lock}

e o thread ready com maior prioridade pode invocar o metodo

synchronized que pretende

I

_{metodo synchronized que v^e que n~ao pode executar chama wait e}

espera numa la

I

_{outro metodo pode reactivar o metodo auto-suspendido}

noticando-o (notify) que pode voltar a correr

(5)

Threads (produtor/consumidor),

sem sincronizac~ao

public class SharedCell f

public static void main(String args[])f HoldInteger h = new HoldInteger();

ProduceInteger p = new ProduceInteger(h); ConsumeInteger c = new ConsumeInteger(h); p.start();

c.start(); g

g

class ProduceInteger extends Threadf private HoldInteger pHold;

public ProduceInteger(HoldInteger h)f pHold = h;

g

public void run()f

for(int count = 0; count < 10; count++)f pHold.setSharedInt(count);

System.out.println("Producer set sharedInt: "+ count); try f Thread.sleep((int) (Math.random() * 3000)); g catch(InterruptedException e) f System.err.println(e.toString()); g g pHold.setMoreData(false); g g

Threads (produtor/consumidor)

(cont.)

sem sincronizac~ao

class ConsumeInteger extends Thread f private HoldInteger cHold;

public ConsumeInteger(HoldInteger h)f cHold = h;

g

public void run()f int val;

while(cHold.hasMoreData())f

tryf Thread.sleep((int) (Math.random() * 3000));g catch(InterruptedException e)f

System.err.println(e.toString()); g

val = cHold.getSharedInt();

System.out.println( "Consumer retrieved " + val ); g

g g

class HoldIntegerf private int sharedInt = -1; private boolean moreData = true;

public void setSharedInt(int val)f sharedInt = val;

g

public int getSharedInt()f return sharedInt; g

public void setMoreData(boolean b)f moreData = b;

g

public boolean hasMoreData()f return moreData;

g g

do livro \Java How to Program", Deitel & Deitel

(6)

Resultado

# java SharedCell

Producer set sharedInt to 0

Producer set sharedInt to 1

Consumer retrieved 1

Producer set sharedInt to 2

Consumer retrieved 2

Producer set sharedInt to 3

Producer set sharedInt to 4

Consumer retrieved 4

Producer set sharedInt to 5

Producer set sharedInt to 6

Consumer retrieved 6

Producer set sharedInt to 7

Consumer retrieved 7

Producer set sharedInt to 8

Consumer retrieved 8

Producer set sharedInt to 9

Consumer retrieved 9

Rui CamachoApresentac~ao Complementos de Programac~ao e Algoritmos { LEIC Java { conceitos Basicos

Threads (produtor/consumidor),

com sincronizac~ao

// Do exemplo anterior so HoldInteger e diferente. class HoldInteger f

private int sharedInt = -1; private boolean moreData = true; //monitor's condition variable private boolean writeable = true;

public synchronized void setSharedInt(int val)f while(!writeable)f try f wait(); g catch(InterruptedException e)f System.err.println("Exception: " + e.toString()); g g sharedInt = val; writeable = false; notify(); g

public synchronized int getSharedInt()f while( writeable ) f try f wait(); g catch(InterruptedException e)f System.err.println("Exception: " + e.toString()); g g writeable = true; notify(); return sharedInt; g

public void setMoreData(boolean b)f moreData = b; g public boolean hasMoreData()f return moreData;g g

(7)

Resultado

# java SharedCell

Producer set sharedInt to 0

Consumer retrieved 0

Producer set sharedInt to 1

Consumer retrieved 1

Producer set sharedInt to 2

Consumer retrieved 2

Producer set sharedInt to 3

Consumer retrieved 3

Producer set sharedInt to 4

Consumer retrieved 4

Producer set sharedInt to 5

Consumer retrieved 5

Producer set sharedInt to 6

Consumer retrieved 6

Producer set sharedInt to 7

Consumer retrieved 7

Producer set sharedInt to 8

Consumer retrieved 8

Producer set sharedInt to 9

Consumer retrieved 9

Buer circular

import java.applet.Applet; import java.awt.*;

import java.text.DecimalFormat;

public class SharedCell extends Appletf private TextArea output;

public void init()f

setLayout(new BorderLayout()); output = new TextArea();

add(output, BorderLayout.CENTER); g

public void start()f

HoldInteger h = new HoldInteger(output); ProduceInteger p = new ProduceInteger(h); ConsumeInteger c = new ConsumeInteger(h); p.start();

c.start(); g

g

class ProduceInteger extends Threadf ... igual ao exemplo anterior ... g

class ConsumeInteger extends Threadf ... igual ao exemplo anterior ...

(8)

Buer circular

class HoldIntegerf

private int sharedInt[] = f -1, -1, -1, -1, -1 g; private boolean moreData = true;

private boolean writeable = true; private boolean readable = false; private int readLoc = 0, writeLoc = 0; private TextArea output;

public HoldInteger(TextArea out)f output = out;

g

public synchronized void setSharedInt(int val)f while( !writeable) f

try f

output.append(" WAITING TO PRODUCE "+val); wait(); g catch(InterruptedException e)f System.err.println(e.toString()); g g sharedInt[writeLoc] = val; readable = true; output.append("nnProduced " + val + " into cell " + writeLoc);

writeLoc = (writeLoc + 1) % 5;

output.append("ntwrite "+writeLoc+"ntread "+readLoc); printBuer(output, sharedInt); if(writeLoc == readLoc)f writeable = false; output.append("nnBUFFER FULL"); g notify(); g

Buer circular

public synchronized int getSharedInt()f int val;

while(!readable)f try f

output.append( " WAITING TO CONSUME" ); wait(); g catch ( InterruptedException e ) f System.err.println( e.toString() ); g g writeable = true; val = sharedInt[readLoc]; output.append("nnConsumed " + val + " from cell " + readLoc); readLoc = (readLoc + 1) % 5;

output.append( "ntwrite " + writeLoc + "ntread " + readLoc); printBuer(output, sharedInt); if(readLoc == writeLoc)f readable = false; output.append("nnBUFFER EMPTY"); g notify(); return val; g

(9)

Buer circular

public void printBuer( TextArea out, int buf[])f

DecimalFormat threeChs = new DecimalFormat(" #;-#"); output.append("ntbuer: ");

for(int i = 0; i < buf.length; i++)

out.append(" " + threeChs.format(buf[i])); g

public void setMoreData(boolean b)f moreData = b;

g

public boolean hasMoreData()f

if (moreData == false && readLoc == writeLoc) return false;

else return true; g

g

Threads Daemon

I

_{s~ao executados para benefcio de outros threads}

I

_{correm em background}

I

_{tornar um thread em daemon: setDaemon(true)}

I

_{a propriedade daemon tem que ser activada antes do metodo start()}

I

_{se so existirem daemons o Java termina}

I

_{ex: garbage collection}

(10)

Interface Runnable

I

_{usar a classe Thread implica heranca dessa classe}

I

_{multithreading sem heranca de Thread ! uso do interface Runnable}

I

_{declarac~ao: class Classe implements Runnable}

I

_{codigo tambem guardado em run()}

I

_{criac~ao: Thread(Runnable object) ou}

Thread(Runnable object, String threadName)

Interface Runnable

{ exemplo {

import java.applet.Applet; import java.awt.*; import java.awt.event.*;

public class RandomCharacters extends Applet implements Runnable, ActionListener f private String alphabet;

private TextField output1, output2, output3; private Button button1, button2, button3; private Thread thread1, thread2, thread3; private boolean suspend1, suspend2, suspend3; public void init()f

alphabet = new String( "ABCD...YZ"); output1 = new TextField(10);

output1.setEditable(false); output2 = new TextField(10); output2.setEditable(false); output3 = new TextField(10); output3.setEditable(false);

button1 = new Button("Suspend/Resume 1"); button1.addActionListener(this);

button2 = new Button("Suspend/Resume 2"); button2.addActionListener(this);

button3 = new Button("Suspend/Resume 3"); button3.addActionListener(this); add(output1); add(button1); add(output2); add(button2); add(output3); add(button3); g

(11)

Interface Runnable

{ exemplo

(cont.)

{

public void start()f

// create threads and start every time start is called

thread1 = new Thread(this, "Thread 1");

thread2 = new Thread(this, "Thread 2");

thread3 = new Thread(this, "Thread 3");

thread1.start();

thread2.start();

thread3.start();

g

public void stop()f

// stop threads every time stop is called

// as the user browses another Web page

thread1.stop();

thread2.stop();

thread3.stop();

g

Interface Runnable

{ exemplo

(cont.)

{

public void actionPerformed(ActionEvent e)f

if(e.getSource() == button1) if(suspend1)f thread1.resume(); suspend1 = false; g else f thread1.suspend(); output1.setText("suspended"); suspend1 = true; g

else if (e.getSource() == button2) if (suspend2) f thread2.resume(); suspend2 = false; g else f thread2.suspend(); output2.setText("suspended"); suspend2 = true; g

else if (e.getSource() == button3) if (suspend3) f thread3.resume(); suspend3 = false; g else f thread3.suspend(); output3.setText("suspended"); suspend3 = true; g g

(12)

Interface Runnable

{ exemplo

(cont.)

{

public void run()f

int location; char display;

Thread executingThread; while (true) f

// sleep from 0 to 5 seconds try f Thread.sleep((int) (Math.random() * 3000)); g catch (InterruptedException e) f e.printStackTrace(); g

location = (int) (Math.random() * 26); display = alphabet.charAt(location); executingThread = Thread.currentThread(); if (executingThread == thread1)

Concorr^encia. A classe Thread (java.lang)

Concorr^encia

I

Concorr^encia em Java

MultiThreading

sincronizac~ao

interface Runnable

grupos de threads

exemplos

A classe Thread

(java.lang)

Os threads s~ao dependentes da plataforma. Correm por quantum de tempo em

Windows e em modo preemptive no Solaris.

Escalonador privilegia as prioridades (entre 0 e 10) mais elevadas. Podem

correr em modo daemon.

I

construtores: Thread(String nome), Thread(Runnable obj), ...

I

metodo run() onde existe o codigo do thread

I

metodo start() inicia o thread e termina

I

static sleep(long MiliSegundos) coloca o thread no estado sleep

I

metodo interrupt()

I

metodos suspend() / resume()

I

metodo stop() termina um thread (n~ao e muito usado)

Estados de um thread

I

ready | pronto a executar quando houver 1 CPU

I

running | em execuc~ao

I

suspended | activavel com chamada a resume()

I

blocked | a espera de uma operac~ao E/S

I

sleeping | sem executar por um perodo pre-determinado

I

waiting

I

dead | terminou a sua execuc~ao

Threads

Threads

{ exemplo simples {

class PrintThread extends Thread f

int sleepTime;

public PrintThread() f

sleepTime = (int) ( Math.random() * 5000 );

System.out.println( "Name: " + getName() +

"; sleep: " + sleepTime );

g

public void run() f

try f

Thread.sleep( sleepTime );

System.out.println(\Dormi durante \+sleepTime+" segundos. Ate ja.");

g

catch (InterruptedException exception) f

System.err.println(exception.toString());

g

System.out.println(getName());

g

g

Threads

{ exemplo simples {

public class PrintTest f

public static void main(String args[])f

PrintThread thread1, thread2, thread3, thread4;

thread1 = new PrintThread();

thread2 = new PrintThread();

thread3 = new PrintThread();

thread4 = new PrintThread();

thread1.start();

thread2.start();

thread3.start();

thread4.start();

g

g

_{Concorr^encia em Java}

sincronizac~ao

_{construtores: Thread(String nome), Thread(Runnable obj), ...}

_{metodo run() onde existe o codigo do thread}

_{metodo start() inicia o thread e termina}

_{static sleep(long MiliSegundos) coloca o thread no estado sleep}

_{metodo interrupt()}

_{metodos suspend() / resume()}

_{metodo stop() termina um thread (n~ao e muito usado)}

_{ready | pronto a executar quando houver 1 CPU}

_{running | em execuc~ao}

_{suspended | activavel com chamada a resume()}

_{blocked | a espera de uma operac~ao E/S}

_{sleeping | sem executar por um perodo pre-determinado}

_waiting

_{dead | terminou a sua execuc~ao}

Sincronizac~ao

_{Uso de monitors (C.A. Hoare)}

_{Cada objecto com um metodo synchronized e um monitor}

_{O monitor deixa um so thread de cada vez correr um metodo}

_{todos os threads que tentam invocar um metodo synchronized}

Sincronizac~ao

_{quando um metodo synchronized termina o monitor levanta o lock}

e o thread ready com maior prioridade pode invocar o metodo

_{metodo synchronized que v^e que n~ao pode executar chama wait e}

_{outro metodo pode reactivar o metodo auto-suspendido}

noticando-o (notify) que pode voltar a correr

sem sincronizac~ao

sem sincronizac~ao

com sincronizac~ao