Hi All,
I have come up with a little different version of this program to understand how synchronized keyword works. I have written this program such that the program exits when the values of i and j are out of sync in SyncData object. If the program doesn't exit then it meens that the values of i and j are in sync.
Though the sync() method is synchronized, the program exits after executing for some time. I don't understand why those values are going out of sync though the sync() is synchronized. Does anyone have any idea?
Following is the program. Just compile and run it.
Thanks,
Srinivas.
package com.test;
public class Controller {
public static void main(String args[]) {
// JVM will have only one instance of SyncData, i.e data
SyncData data = SyncData.getInstance();
Worker w1 = new Worker(data, true);
w1.kickStart();
Thread.yield();
Worker w2 = new Worker(data, false);
w2.kickStart();
Thread.yield();
while(true) {
if(data.inSync()) {
System.out.println("In Sync, i = " + data.getI() + " and j = " + data.getJ() + " continuing...");
}
else {
System.out.println("Not in Sync, i = " + data.getI() + " and j = " + data.getJ());
w1.terminate();
w2.terminate();
break;
}
}
}
}
class Worker implements Runnable {
private SyncData data;
private boolean forward;
private Thread theThread;
public Worker(SyncData data, boolean forward) {
this.data = data;
this.forward = forward;
}
public void kickStart() {
if(theThread==null) {
theThread=new Thread(this);
theThread.start();
}
}
public void terminate() {
theThread=null;
}
public void run() {
double d = 0.0D;
while(theThread==Thread.currentThread()) {
if(forward) {
d = d + 1;
}
else {
d = d - 1;
}
this.data.sync(d);
}
}
}
//Its a singleton, to make sure JVM has only one instance of it.
class SyncData {
private static SyncData data;
private SyncData() {
}
public static SyncData getInstance() {
if(data == null) {
data = new SyncData();
}
return data;
}
private double i = 0;
private double j = 0;
// Makes sure that i and j are always in sync.
// This is synchronized to make sure i and j are always in sync.
// But doesn't seem to work.
// What am I missing?
public void sync(double syncValue) {
synchronized (this) {
System.out.println("Sync called with " + syncValue);
this.i = syncValue;
// Kill some time. Don't yeild.
for(int x=0; x<1000; x++) {
new Object();
}
this.j = syncValue;
}
}
public boolean inSync() {
return i==j;
}
public double getI() {
return i;
}
public double getJ() {
return j;
}
}
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