cs480_110211

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cs480 (Prasad) L11Threads 1

Cooperative Concurrent Threads

Producer-Consumer Problem

Bounded-Buffer Problem

(Clients and Servers : Resource Sharing)

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Simplistic 1-Cell Buffer

class Buffer {Object x;

// synchronized

public void put (Object _x, String id) {

System.out.println(

"Done > " + id + " gets " + x);return x;

}

}

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class Producer extends Thread {

private Random r = new Random();

Buffer b; String id;public Producer(Buffer _b, String _id) {

b = _b; id = _id;

}

public void run () {

int delay; Integer ir;

try {

while (true) {

delay = Math.abs(r.nextInt() % 1999) + 50;

sleep(delay); ir = new Integer(delay);

System.out.println("Ready

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class Consumer extends Thread {

private Random r = new Random();

Buffer b; String id;

public Consumer(Buffer _b, String _id) {

b = _b; id = _id;

}


int delay; Integer ir = null;

try

{while (true) {

delay = Math.abs(r.nextInt() % 1999) + 50;

sleep(delay);

System.out.println("Ready >> " + id + " gets ");

ir = (Integer) b.get(id);

}} catch (Exception e) {System.out.println("Exception$ " + e);};

}

}

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Producer-Consumer : Bounded Bufferpublic class PCB {public static void main(String[] args) {

Buffer b = new Buffer();

new Consumer(b,"C1") . start();

new Producer(b,"P1") . start();

try {Thread.sleep(1000);

} catch (Exception e){};

new Consumer(b,"C2") . start();

new Producer(b,"P2") . start();

}

}

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Unfettered Run

Ready >> C1 gets

Ready > C1 gets null

Done > C1 gets

Done >> C1 gets 488

Ready >> C2 getsDone >> C2 gets 488

Ready C2 gets 815Ready C1 gets

Done >> C1 gets 1223

Ready C2 gets

Done >> C2 gets 403

...

(transient stability?!)premature

puts

gets

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Concurrency control : class Bufferclass Buffer {

Object x;boolean empty = true;public synchronized void put

(Object _x, String id) throws Exception{ ...}

public synchronized Object get

(String id) throws Exception { ... }}

Two producers (consumers) cannot put(get) twoitems in (from) the same buffer slotsimultaneously.

Two producers (consumers) cannot put(get) twoitems in (from) the same buffer slot without anintervening consumer (producer).

A consumer (producer) is not permitted to get(put)an item from (into) buffer if empty (full).

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public synchronized void

put (Object _x, String id) throws Exception {

while (!empty) wait();

empty = ! empty;

System.out.println("Done

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public synchronized Object

get (String id) throws Exception {while (empty) wait();

empty = ! empty;

System.out.println("Done >> "+id+" gets "+x);

notifyAll();return x;

}

Note that notify cannot always be used inplace ofnotifyAll because a consumer may be woken up.

while required because notifyAlldue to a producerdoes not guarantee that wait-ing consumers will find anitem in the buffer.

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Synchonization and Mutual Exclusion

Ready >> C2 gets

Ready >> C1 gets

Ready C2 gets 1672

Ready C1 gets 774

Ready C1 gets

Done >> C1 gets 168

Ready C1 gets

Done >> C1 gets 1263

...

Ready C1 gets

Done >> C1 gets 622

Ready >> C2 gets

Ready C2 gets 1447

Ready > C1 gets 96

Done

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Methods in class Object

public final void wait() throwsInterruptedException {...}

Current thread is suspended (afteratomicallyreleasing the lock on this) until some other thread

invokes notify()ornotifyAll()orinterrupts.

public final void notify() {...}Notifies exactly one thread waiting on thisobject for

a condition to change. The awakened thread cannot

proceed until this thread relinquishes the lock.

public final void notifyAll() {...} These methods must be invoked inside synchronized

code or else IllegalMonitorStateExceptionwill be thrown.

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Single Cell Buffer in C#

using System;

using System.Threading;

class Buffer {

Object x;

bool empty = true;

public void put (Object _x, string id) {

lock(this){

while (!empty) Monitor.Wait(this);

empty = ! empty;

Console.WriteLine("Done > " + id + " gets " + x);

Monitor.PulseAll(this);

return x;

}

}

}

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class Producer {

private System.Random r = new System.Random();


public Producer(Buffer _b, String _id) {

b = _b; id = _id;

}


int delay;

try {

while (true) {

delay = r.Next(2000) + 50;

Thread.Sleep(delay);

Console.WriteLine("Ready

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class Consumer {

private System.Random r = new System.Random();


public Consumer(Buffer _b, String _id) {

b = _b; id = _id;

}


int delay;

try {

while (true) {

delay = r.Next(2000) + 50;

Thread.Sleep(delay);

Console.WriteLine("Ready >> " + id + " gets ");

delay = (int) b.get(id);

}

} catch (Exception e)

{Console.WriteLine("Exception$ " + e);};

}

}

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public class PCB {

public static void Main(string[] args) {

Buffer b = new Buffer();

new Thread( new ThreadStart(new Consumer(b,"C1").run)) . Start();

new Thread( new ThreadStart(new Producer(b,"P1").run)) . Start();

try {Thread.Sleep(1000);}

catch (Exception e){Console.WriteLine("Exception$ " + e);};

new Thread( new ThreadStart(new Consumer(b,"C2").run)) . Start();

new Thread( new ThreadStart(new Producer(b,"P2").run)) . Start();

}

}

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cs480 (Prasad) LSysVsScipt 16

Scripting vs Systems Programming

Languages

Designed for gluingapplications : flexibility

Interpreted Dynamic variable creation Data and code integrated :

meta-programmingsupported

Dynamic typing (typeless) Examples: PERL, Tcl,

Python, Ruby, Scheme,Visual Basic, etc

Designed for buildingapplications : efficiency

Compiled Variable declaration Data and code separated :

cannot create/run code onthe fly

Static typing Examples: PL/1, Ada,

Java, C/C++, C#, etc

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(contd)

Does application implement complex algorithms and datastructures?

Does application process large data sets (>10,000 items)? Are application functions well-defined, fixed?If yes, consider a system programming language.

Is the main task to connect components, legacy apps? Does the application manipulate a variety of things? Does the application have a GUI? Are the application's functions evolving rapidly? Must the application be extensible? Does the application do a lot of string manipulation?If yes, consider a scripting language.

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Current Trends

Hybrid Languages : Scripting + Systems Programming Recent JVM-based Scripting Languages

Jython : Python dialectClojure : LISP dialectScala : OOP +Functional Hybrid

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Jython (for convenient access to Java APIs)

I:\tkprasad\cs480>jython

Jython 2.1 on java1.4.1_02 (JIT: null)

Type "copyright", "credits" or "license" for more information.

>>> import javax.swing as swing

>>> win = swing.JFrame("Welcome to Jython")

>>> win.size = (200, 200)

>>> win.show()>>> ^Z

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Java vs Jython

map = new HashMap();map.put("one",new Integer(1));map.put("two",new Integer(2));map.put("three",new Integer(3));

System.out.println(map.get("one"));

list = new LinkedList();

list.add(new Integer(1));list.add(new Integer(2));list.add(new Integer(3));

map = {"one":1,"two":2,"three":3}

print map ["one"]

list = [1, 2, 3]

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(contd)

for i in list:

(* iterator *)

newList =[function(i) for i in oldList]

(* list comprehension *)

for (Iterator i; i.hasNext();){

i.next();

}

List newList = ArrayList()for (Iterator i; i.hasNext();){

Object obj = i.next();newList.add(function(obj))

}

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Defining functions and expressions in Jython

(file: eg.py)

list =[pow(i,i) for i in [1,2]]

from math import *print PI=%f, e=%f % (pi,e)

Y = range(1,9,1)# [1,2,3,4,5,6,7,8]Y[1:3]#[2, 3]Y[::2]

#[1, 3, 5, 7]

def fac(x) :factorial functionif x

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More Jython code examples

Dynamic code evaluationprint eval ([1,3] + range(6,10,3))

# [1, ,3, 6, 9]

x = 2 + 3j

exec x = 5, x + x

#(5, (4+6j)

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Contd

Exceptionsdef readfile (name):return lines in file or None if unreadable

try: file = open(name, r)try: # raise IOError

return file.readlines()finally:

file.close()except IOError, ioe:

print Exception , ioe

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Contd

Functional Programmingapply(lambda x,y : x*y, (10, 20))

# 200

map(lambda x,y: x + y, [[1,2],[a]], [[3],[b]])# [[1, 2, 3], [a, b]]

reduce(lambda x,y: x + y, [1,2,3], 100)

# 106

filter(lambda x: x > 0, range(10,-5,-3))# [10, 7 , 4, 1]

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import java.lang as langimport javax.swing as swingimport java.awt as awt

names = ["Groucho", "Chico", "Harpo"]

quotes = {"Groucho": "Say the secret word", "Chico": "Viaduct?","Harpo": "HONK!"}

def buttonPressed(event):field.text = quotes[event.source.text]

def exit(event):lang.System.exit(0)

def createButton(name):return swing.JButton(name, preferredSize=(100,20),actionPerformed=buttonPressed)

Java functionality through Jython

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win = swing.JFrame("Welcome to Jython", size=(200,200),windowClosing=exit)

win.contentPane.layout = awt.FlowLayout( )

field = swing.JTextField(preferredSize=(200,20))win.contentPane.add(field)

buttons = [createButton(each) for each in names]

for eachButton in buttons:win.contentPane.add(eachButton)

win.pack( )win.show( )

cs480_110211

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