Semaphore
{
class public Semaphore() { this(1); }
public Semaphore(int i) { value = i; }
public synchronized void P() {
while (value <= 0) {
try { wait(); }
catch (InterruptedException e) {}
}
value--;
}
public synchronized void V() {
value++;
notify();
}
private int value;
}
enum Phase {ODD, EVEN}
public class Taskb implements Runnable
{
Phase phase;
int count;
Semaphore sync;
public Taskb(Phase phase, int count, Semaphore sync)
{
this.phase = phase;
this.count = count;
this.sync = sync;
}
public void run()
{
switch (phase) {
case ODD:
for (int i = 1; i < count; i += 2) {
// print i's value twice without interruption
sync.P();
System.out.println(i);
System.out.println(i);
sync.V();
break;
}
case EVEN:
for (int i = 0; i < count; i += 2) {
// print i's value twice without interruption
sync.P();
System.out.println(i);
System.out.println(i);
sync.V();
}
}
}
static public void main(String[] args)
{
if (args.length != 1) {
System.out.println("Usage: java Taskb <count>");
System.exit(1);
}
Semaphore sem1 = new Semaphore(1);
int count = ...