FCFS ও SJF শিডিউলিং

# FCFS ও SJF শিডিউলার -- সত্যিকারের অ্যালগরিদম, টয় প্রসেস ডেটার উপর, কোনো real OS কল নয়
processes = [
    # (নাম, arrival_time, burst_time)
    ("P1", 0, 7),
    ("P2", 1, 2),
    ("P3", 2, 1),
    ("P4", 3, 4),
]

def fcfs(processes):
    procs = sorted(processes, key=lambda p: p[1])   # arrival অনুযায়ী ক্রম
    time = 0
    results = []
    for name, arrival, burst in procs:
        start = max(time, arrival)
        completion = start + burst
        waiting = start - arrival
        turnaround = completion - arrival
        time = completion
        results.append((name, arrival, burst, start, completion, waiting, turnaround))
    return results

def sjf_nonpreemptive(processes):
    remaining = list(processes)
    time = 0
    results = []
    done_names = set()
    while len(done_names) < len(remaining):
        available = [p for p in remaining if p[1] <= time and p[0] not in done_names]
        if not available:
            future = [p for p in remaining if p[0] not in done_names]
            time = min(p[1] for p in future)     # পরবর্তী arrival পর্যন্ত এগিয়ে যাওয়া
            continue
        chosen = min(available, key=lambda p: p[2])   # সবচেয়ে ছোট burst
        name, arrival, burst = chosen
        start = time
        completion = start + burst
        waiting = start - arrival
        turnaround = completion - arrival
        time = completion
        results.append((name, arrival, burst, start, completion, waiting, turnaround))
        done_names.add(name)
    return results

def print_schedule(title, results):
    print(f"--- {title} ---")
    print(f"{'নাম':4}{'arrival':9}{'burst':7}{'start':7}{'completion':12}{'waiting':9}{'turnaround':10}")
    for name, arrival, burst, start, completion, waiting, turnaround in results:
        print(f"{name:4}{arrival:<9}{burst:<7}{start:<7}{completion:<12}{waiting:<9}{turnaround:<10}")
    avg_wait = sum(r[5] for r in results) / len(results)
    avg_turn = sum(r[6] for r in results) / len(results)
    print(f"গড় waiting time    = {avg_wait:.2f}")
    print(f"গড় turnaround time = {avg_turn:.2f}\n")
    return avg_wait

fcfs_results = fcfs(processes)
avg_wait_fcfs = print_schedule("FCFS", fcfs_results)

sjf_results = sjf_nonpreemptive(processes)
avg_wait_sjf = print_schedule("SJF (non-preemptive)", sjf_results)

print("=== তুলনা ===")
print(f"FCFS গড় waiting time = {avg_wait_fcfs:.2f}")
print(f"SJF  গড় waiting time = {avg_wait_sjf:.2f}")
print("SJF <= FCFS (গড় waiting time)?", avg_wait_sjf <= avg_wait_fcfs)