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public class Volatile extends Object implements Runnable {
// not marked as 'volatile', but it should be!
private int value;
private volatile boolean missedIt;
// doesn't need to be volatile-doesn't change
private long creationTime;
public Volatile() {
value = 10;
missedIt = false;
creationTime = System.currentTimeMillis();
}
public void run() {
print("entering run()");
// each time, check to see if 'value' is different
while (value < 20) {
// Used to break out of the loop if change to
// value is missed.
if (missedIt) {
int currValue = value;
// Simply execute a synchronized statement on an
// arbitrary object to see the effect.
Object lock = new Object();
synchronized (lock) {
// do nothing!
}
int valueAfterSync = value;
print("in run() - see value=" + currValue
+ ", but rumor has it that it changed!");
print("in run() - valueAfterSync=" + valueAfterSync);
break;
}
}
print("leaving run()");
}
public void workMethod() throws InterruptedException {
print("entering workMethod()");
print("about to sleep for 2 seconds");
Thread.sleep(2000);
value = 50;
print("just set value=" + value);
print("about to sleep for 5 seconds");
Thread.sleep(5000);
missedIt = true;
print("just set missedIt=" + missedIt);
print("about to sleep for 3 seconds");
Thread.sleep(3000);
print("leaving workMethod()");
}
private void print(String msg) {
long interval = System.currentTimeMillis() - creationTime;
String tmpStr = (interval / 1000.0) + "000";
int pos = tmpStr.indexOf(".");
String secStr = tmpStr.substring(pos - 2, pos + 4);
String nameStr = Thread.currentThread().getName();
nameStr = nameStr.substring(nameStr.length() - 8, nameStr.length());
System.out.println(secStr + " " + nameStr + ": " + msg);
}
public static void main(String[] args) {
try {
Volatile vol = new Volatile();
// slight pause to let some time elapse
Thread.sleep(100);
Thread t = new Thread(vol);
t.start();
// slight pause to allow run() to go first
Thread.sleep(100);
vol.workMethod();
} catch (InterruptedException x) {
System.err.println("one of the sleeps was interrupted");
}
}
}
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