I have some code that generates threads (lizards)
it also makes a cat thread.
the cat checks on the lizards (once it wakes up) and if there are to many crossing a path at one time it eats them. the idea is to have the lizards cross and eat while the world has not ‘ended’ with out interruption from the cat thread.
I need to use semaphores to control this.
I have the idea down just need that extra push so I can start taking a crack of it.
Ive edited to code to show where my issues are.
import java.util.ArrayList;
import java.util.concurrent.Semaphore;
import java.util.logging.Level;
import java.util.logging.Logger;
public class LizardsSync
{
/*
* Set this to the number of seconds you want the lizard world to
* be simulated.
* Try 30 for development and 120 for more thorough testing.
*/
private static int WORLDEND = 30;
/*
* Number of lizard threads to create
*/
private static int NUM_LIZARDS =20;
/*
* Maximum lizards crossing at once before alerting cats
*/
private static int MAX_LIZARD_CROSSING = 4;
/*
* Maximum seconds for a lizard to sleep
*/
private static int MAX_LIZARD_SLEEP_TIME = 3;
/*
* Maximum seconds for a lizard to eat
*/
private static int MAX_LIZARD_EAT_TIME = 5;
/*
* Number of seconds it takes to cross the driveway
*/
private static int CROSS_TIME = 2;
/*
* Number of seconds for the cat to sleep.
*/
private static int MAX_CAT_SLEEP;
/*
* A counter that counts the number of lizzards crossing sago to monkey grass
*/
int numCrossingSago2MonkeyGrass = 0;
/*
* A counter that counts the number of lizzards crossing monkey grass to sago
*/
int numCrossingMonkeyGrass2Sago = 0;
/**
* A semaphore to protect the crossway.
* only the max amount of lizards can cross so the cat wont 'play'
*/
Semaphore semaphoreCrossway = new Semaphore(MAX_LIZARD_CROSSING,true);
/**
* A semaphore for mutual exclusion.
*/
Semaphore mutex = new Semaphore(4);
// on both semaphores, you can call acquire() or release()
/*
* Indicates if the world is still running.
*/
private static boolean running = true;
/*
* Indicates if you want to see debug information or not.
*/
private static boolean debug = true;
public void go()
{
ArrayList<Thread> allThreads = new ArrayList<Thread>();
// create all the lizzard threads
for (int i=0; i < NUM_LIZARDS; i++)
{ allThreads.add(new LizardThread(i) );
allThreads.get(i).start();
}
// create the cat thread
Thread CatThread = new CatThread();
CatThread.start();
// let the world run for a while
sleep (WORLDEND);
// terminate all threads
running = false;
// wait until all threads terminate by joining all of them
for (int i=0; i < NUM_LIZARDS; i++) {
try {
allThreads.get(i).join();
} catch (InterruptedException ex) {
System.err.println ("unable to join thread, " + ex.getMessage());
}
}
}
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
// starts the program
new LizardsSync().go();
}
/**
* Models a cat thread.
*/
public class CatThread extends Thread {
/**
* @see java.lang.Runnable.
*/
@Override
public void run()
{
// you must finish this method
while (running) {
// sleep for a while
catSleep();
// check on lizzards
checkCrossway();
}
}
/**
* Puts cat thread to sleep for a random time.
*/
public void catSleep()
{
int sleepSeconds = 1 + (int)(Math.random()*MAX_CAT_SLEEP);
if (debug) {
System.out.println ("Cat is sleeping for " + sleepSeconds + " seconds.");
System.out.flush();
}
try {
sleep(sleepSeconds*1000);
} catch (InterruptedException ex) {
Logger.getLogger(LizardsSync.class.getName()).log(Level.SEVERE, null, ex);
}
if (debug) {
System.out.println ("Cat awakes.");
System.out.flush();
}
}
/**
* Simulates cat checking the crossway.
*/
public void checkCrossway()
{
if (numCrossingMonkeyGrass2Sago + numCrossingSago2MonkeyGrass > MAX_LIZARD_CROSSING) {
System.out.println ("The cat says yum!");
System.out.flush();
System.exit(-1);
}
}
}
/**
* Models a lizard thread.
*/
public class LizardThread extends Thread {
private int _id;
/**
* Creates a new lizard thread.
*
* @param id the id assigned to the lizard thread
*/
public LizardThread(int id)
{
_id = id;
}
/**
* @see java.lang.Runnable.
*/
@Override
public void run()
{
while (running) {
// sleep for a while in sago
lizardSleep();
// wait until safe to cross from sago to monkey grass
sagoToMonkeyIsSafe();
// cross path to monkey grass
crossedOverToMonkey();
// eat in the monkey grass
lizardEat();
// wait untill its safe to cross back to sago
monkeyToSagoIsSafe();
// cross from cross monkey grass to sage
crossMonkeyToSago();
}
}
/**
* This tests if it is safe to travel from sago to monkey.
* Finish this.
*/
public void sagoToMonkeyIsSafe()
{
if (debug) {
System.out.println ("Lizard [" + _id + "] checks sago -> monkey grass.");
System.out.flush();
}
// you must add code here
// use a semaphore
if (debug) {
System.out.println ("Lizard [" + _id + "] thinks sago -> monkey grass is safe.");
System.out.flush();
}
}
/**
* Indicates that lizard crossed over to monkey grass.
* Finish this.
*/
public void crossedOverToMonkey()
{
if (debug) {
System.out.println ("Lizard [" + _id + "] made it to monkey grass.");
System.out.flush();
}
// add code here
}
/**
* This tests if it is safe to travel from monkey to sago.
* Finish this.
*/
public void monkeyToSagoIsSafe()
{
if (debug) {
System.out.println ("Lizard [" + _id + "] checks monkey grass -> sago.");
System.out.flush();
}
// you must add code here
// use a semaphore
if (debug) {
System.out.println ("Lizard [" + _id + "] thinks monkey grass -> sago is safe.");
System.out.flush();
}
}
/**
* Indicates that lizard crossed over to sago.
* Finish this.
*/
public void crossedOverToSago()
{
if (debug) {
System.out.println ("Lizard [" + _id + "] made it to sago.");
System.out.flush();
}
// add code here
}
/**
* Indicates that lizard is crossing over from monkey to sago.
* Finish this
*/
void crossMonkeyToSago()
{
if (debug) {
System.out.println ("Lizard [" + _id + "] is crossing monkey grass to sago.");
System.out.flush();
}
numCrossingMonkeyGrass2Sago++;
// simulate walk
try {
sleep(CROSS_TIME*1000);
} catch (InterruptedException ex) {
Logger.getLogger(LizardsSync.class.getName()).log(Level.SEVERE, null, ex);
}
numCrossingMonkeyGrass2Sago--;
}
/**
* Indicates that lizard is crossing over from sago to monkey.
*/
void crossSagoToMonkey()
{
if (debug) {
System.out.println ("Lizard [" + _id + "] is crossing sago to monkey grass.");
System.out.flush();
}
numCrossingSago2MonkeyGrass++;
// simulate walk
try {
sleep(CROSS_TIME*1000);
} catch (InterruptedException ex) {
Logger.getLogger(LizardsSync.class.getName()).log(Level.SEVERE, null, ex);
}
numCrossingSago2MonkeyGrass--;
}
/**
* Puts lizard thread to sleep for a random amount of time.
*/
public void lizardSleep()
{
int sleepSeconds = 1 + (int)(Math.random()*MAX_LIZARD_SLEEP_TIME);
if (debug) {
System.out.println ("Lizard [" + _id + "] is sleeping for " + sleepSeconds + " seconds.");
System.out.flush();
}
try {
sleep(sleepSeconds*1000);
} catch (InterruptedException ex) {
Logger.getLogger(LizardsSync.class.getName()).log(Level.SEVERE, null, ex);
}
if (debug) {
System.out.println ("Lizard [" + _id + "] awakes.");
System.out.flush();
}
}
/**
* Simulates lizard eating for a random amount of time.
*/
public void lizardEat()
{
int eatSeconds = 1 + (int)(Math.random()*MAX_LIZARD_EAT_TIME);
if (debug) {
System.out.println ("Lizard [" + _id + "] is eating for " + eatSeconds + " seconds.");
System.out.flush();
}
try {
sleep(eatSeconds*1000);
} catch (InterruptedException ex) {
Logger.getLogger(LizardsSync.class.getName()).log(Level.SEVERE, null, ex);
}
if (debug) {
System.out.println ("Lizard [" + _id + "] finished eating.");
System.out.flush();
}
}
}
/**
* Puts current thread to sleep for a specified amount of time.
*
* @param seconds the number of seconds to put the thread to sleep
*/
private static void sleep(int seconds)
{
try {
Thread.sleep(seconds*1000);
} catch (InterruptedException ex) {
Logger.getLogger(LizardsSync.class.getName()).log(Level.SEVERE, null, ex);
}
}
}
this code as of now writes something like this
Cat awakes.
The cat says yum!
Lizard [8] finished eating.
Lizard [0] is sleeping for 1 seconds.
Lizard [8] checks monkey grass -> sago.
Lizard [1] finished eating.
Lizard [8] thinks monkey grass -> sago is safe.
Lizard [1] checks monkey grass -> sago.
Lizard [8] is crossing monkey grass to sago.
Lizard [1] thinks monkey grass -> sago is safe.Java Result: -1
BUILD SUCCESSFUL (total time: 5 seconds)
This is exactly what
java.util.concurrent.Semaphoreis for.