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CriticalSection.java
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172 lines (128 loc) · 3.67 KB
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package concurrency;
import java.util.concurrent.*;
import java.util.concurrent.atomic.*;
import java.util.*;
/**
* RUN:
* javac concurrency/CriticalSection.java && java concurrency.CriticalSection
*
* OUTPUT:
* pm1: Pair: x: 37, y: 37 checkCounter = 610
* pm2: Pair: x: 38, y: 38 checkCounter = 18281499
*/
public class CriticalSection {
static void testApproaches(PairManager pman1, PairManager pman2) {
ExecutorService exec = Executors.newCachedThreadPool();
PairManipulator pm1 = new PairManipulator(pman1);
PairManipulator pm2 = new PairManipulator(pman2);
PairChecker pcheck1 = new PairChecker(pman1);
PairChecker pcheck2 = new PairChecker(pman2);
exec.execute(pm1);
exec.execute(pm2);
exec.execute(pcheck1);
exec.execute(pcheck2);
try {
TimeUnit.MILLISECONDS.sleep(500);
}
catch (InterruptedException e) {
System.out.println("Sleep interrupted");
}
System.out.println("pm1: "+pm1 +"\npm2: "+pm2);
System.exit(0);
}
public static void main(String[] args) {
PairManager pman1 = new PairManager1();
PairManager pman2 = new PairManager2();
testApproaches(pman1, pman2);
}
}
// NOT THREAD-SAVE
class Pair {
private int x, y;
public Pair(int x, int y) {
this.x = x;
this.y = y;
}
public Pair() { this(0, 0); }
public int getX() { return x; }
public int getY() { return y; }
public void incrementX() { x++; }
public void incrementY() { y++; }
public String toString() {
return "x: " + x + ", y: " + y;
}
public class PairValuesNotEqualException extends RuntimeException {
public PairValuesNotEqualException() {
super("Pair values not equal: " + Pair.this);
}
}
public void checkState() {
if (x != y) {
throw new PairValuesNotEqualException();
}
}
}
// protection for Pair.class inside thread-save class
abstract class PairManager {
AtomicInteger checkCounter = new AtomicInteger(0);
protected Pair p = new Pair();
private List<Pair> storage = Collections.synchronizedList(new ArrayList<Pair>());
public synchronized Pair getPair() {
// create copy for secure original
return new Pair(p.getX(), p.getY());
}
protected void store(Pair p) {
storage.add(p);
try {
TimeUnit.MILLISECONDS.sleep(50);
}
catch (InterruptedException e) {
//
}
}
public abstract void increment();
}
class PairManager1 extends PairManager {
public synchronized void increment() {
p.incrementX();
p.incrementY();
store(getPair());
}
}
class PairManager2 extends PairManager {
public void increment() {
Pair temp;
synchronized(this) {
p.incrementX();
p.incrementY();
temp = getPair();
}
store(temp);
}
}
class PairManipulator implements Runnable {
private PairManager pm;
public PairManipulator(PairManager pm) {
this.pm = pm;
}
public void run() {
while (true) {
pm.increment();
}
}
public String toString() {
return "Pair: " + pm.getPair() + " checkCounter = " + pm.checkCounter.get();
}
}
class PairChecker implements Runnable {
private PairManager pm;
public PairChecker(PairManager pm) {
this.pm = pm;
}
public void run() {
while (true) {
pm.checkCounter.incrementAndGet();
pm.getPair().checkState();
}
}
}