private void step() {
int q = this.quantum;
int used;
Process proc;
// we MUST process the queues in reverse order for two reasons
// - so a process can't get promoted and re-calculated in another queue
// - so our wait times don't get messed up
for (int i = level.size() - 1; i >= 0; i--) {
// retrieve first item (does not remove!)
proc = level.get(i).peek();
// no process? good bye
if (proc == null) {
continue;
}
// how much of the quantum do we need to use?
used = q < proc.getBurstTime() ? q : proc.getBurstTime();
proc.changeBurstTime(-1 * used);
// finished and in the last fifo queue...
if (i == level.size() - 1) {
// and we're finished, lets remove this process
if (proc.getBurstTime() == 0) {
level.get(level.size() - 1).poll();
}
}
// if we aren't finished and are not in the last queue
// remove from current queue and move to next queue
else {
level.get(i).poll();
level.get(i + 1).offer(proc);
}
// finally, we add all the wait times to the other processes
// synchronized(level.get(i)) {
for (Process p : level.get(i)) {
if (p != proc) {
p.addWaitTime(used);
}
}
// }
}
}
public static void main(String[] args) {
final String PROCESSES_FILE = "processes.txt";
final int TIME_QUANTUM = 2;
// Read processes in from the file and add them to the ready queue.
Queue<Process> readyQueue = new LinkedList<Process>();
for (int i = 0; i < 20; i++) {
readyQueue.add(new Process(i, i + 20, i + 13, 0.3));
}
int ticker = 0;
CPU cpu = new CPU();
Process process = readyQueue.poll();
while (readyQueue.size() > 0) {
if (process.getState() == ProcessState.TERMINATED) {
readyQueue.remove(process);
process = readyQueue.poll();
} else if (process.getBurstTime() % TIME_QUANTUM == 0) {
// Put the current process in ready state and add it back to
// the queue
process.setState(ProcessState.READY);
readyQueue.add(process);
process = readyQueue.poll();
}
process.setState(ProcessState.RUNNING);
try {
cpu.setPC(process.generateInstruction());
cpu.setRegisters(process.generateRegisters());
process.incrementBurstTime();
System.out.print("CPU at " + ticker + ": " + cpu + " on pid: " + process.getPid() + "\n");
} catch (Exception e) {
System.out.println(e.getMessage());
}
ticker++;
}
}
