CPU Scheduling Criteria

// Calculating scheduling metrics for 3 processes (non-preemptive)
// Process | Arrival | Burst
//    P1   |    0    |   6
//    P2   |    2    |   3
//    P3   |    4    |   1
// FCFS order: P1, P2, P3

// Gantt chart:
// | P1 (0-6) | P2 (6-9) | P3 (9-10) |
//   0         6          9           10

int[] arrival  = {0, 2, 4};
int[] burst    = {6, 3, 1};
int[] start    = {0, 6, 9};   // when each process first gets CPU
int[] finish   = {6, 9, 10};  // when each process completes

int n = 3;
double totalTurnaround = 0, totalWait = 0;
for (int i = 0; i < n; i++) {
    int turnaround = finish[i] - arrival[i];   // finish - arrival
    int waiting    = turnaround - burst[i];    // turnaround - burst
    System.out.printf("P%d → Turnaround: %d, Waiting: %d%n",
        i + 1, turnaround, waiting);
    totalTurnaround += turnaround;
    totalWait       += waiting;
}
System.out.printf("Avg Turnaround: %.1f%n", totalTurnaround / n);
System.out.printf("Avg Waiting:    %.1f%n", totalWait / n);
// Avg Turnaround: 5.67   Avg Waiting: 2.67

// Demonstrating response time importance in interactive systems
// Response time = time from request to first byte of response

// BAD: one long task blocks all short tasks (poor response time)
// | LONG_TASK (0–100ms) | SHORT1 (100–101ms) | SHORT2 (101–102ms) |
// Response time for SHORT1 = 100ms — user notices lag

// GOOD: Round Robin gives every task CPU time quickly
// | LONG(0-10) | SHORT1(10-11) | SHORT2(11-12) | LONG(12-22) | ...
// Response time for SHORT1 = 10ms — snappy

// Java: measuring task response time with CompletableFuture
long submitTime = System.nanoTime();
CompletableFuture<String> future = CompletableFuture.supplyAsync(() -> {
    // simulate work
    return "result";
});
future.thenAccept(result -> {
    long responseTime = System.nanoTime() - submitTime;
    System.out.printf("Response time: %.2f ms%n", responseTime / 1e6);
});