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Note that when thread 2 goes into wait, the condition predicate of thread 1 has become false. When notify() is invoked by thread 3, it can be delivered to either thread 1 or thread 2 depending on the JVM. If thread 1 is chosen, it's condition turns out to be false. Even though this notify was meant for thread 2 (whose condition is on the other hand, true) thread 1 wakes up on its false condition.
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import java.util.LinkedList;
import java.io.IOException;
public class MissedSignal implements Runnable{
private static LinkedList list = new LinkedList();
private static int buffer_count = 5;
private int number; //selects function based on thread number
public MissedSignal(int number) {
this.number = number;
}
public void run (){
synchronized(list) {
try {
if(number == 1) {
System.out.println("Thread 1 started...");
while(buffer_count == 0) {
System.out.println("Beginning wait() Thread 1...");
list.wait();
System.out.println("Thread 1 got notified this time...");
}
System.out.println("Exiting because Thread 1 condition is false...");
}
else if(number == 2) {
System.out.println("Thread 2...");
while(buffer_count > 0) {
System.out.println("Beginning wait() Thread 2...");
list.wait();
System.out.println("Thread 2 got notified this time...");
}
System.out.println("Exiting because the thread 2 condition is false...");
}
else if(number == 3) {
Thread.sleep(2000);
list.notify();
}
}catch (InterruptedException ie) {ie.printStackTrace(); }
}
}
public static void makeThread1True() {
buffer_count = 0;
}
public static void makeThread2True() {
buffer_count = 10;
}
public static void main(String[] args) throws IOException {
makeThread1True();
Runnable runnable1 = new MissedSignal(1);
Thread t1 = new Thread(runnable1);
t1.start();
try {
new Thread().sleep(5000);
makeThread2True();
} catch (InterruptedException e) { e.printStackTrace(); }
Runnable runnable2 = new MissedSignal(2);
Thread t2 = new Thread(runnable2);
t2.start();
Runnable runnable3 = new MissedSignal(3);
Thread t3 = new Thread(runnable3);
t3.start();
}
}
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