Discrete Event Simulation

des.py

import heapq

class Task:
    def __init__(self, task_id, arrival_time, duration, priority):
        self.task_id = task_id
        self.arrival_time = arrival_time
        self.duration = duration
        self.priority = priority
        self.start_time = None
        self.end_time = None

    def __lt__(self, other):
        return self.priority < other.priority

class Event:
    def __init__(self, time, event_type, task):
        self.time = time
        self.event_type = event_type
        self.task = task

    def __lt__(self, other):
        return self.time < other.time

    def __repr__(self):
        return f"Event(type={self.event_type}, time={self.time}, task={self.task.task_id})"

class Scheduler:
    def __init__(self):
        self.event_queue = []
        self.ready_queue = []
        self.clock = 0
        self.cpu_busy = False
        self.completed_tasks = []

    def schedule_event(self, event):
        heapq.heappush(self.event_queue, event)
        # print(f"[DEBUG] Pushed event {event}.")

    def add_task(self, task):
        arrival_event = Event(task.arrival_time, "arrival", task)
        self.schedule_event(arrival_event)

    def run(self):
        while self.event_queue:
            event = heapq.heappop(self.event_queue)
            # print(f"[DEBUG] Processing event {event}")
            self.clock = event.time
            if event.event_type == 'arrival':
                self.handle_arrival(event.task)
            elif event.event_type == 'complete':
                self.handle_complete(event.task)
        else:
            print("Broke out of event loop since no more events.")


    def handle_arrival(self, task):
        print(f"[{self.clock}] Task {task.task_id} arrived.")
        # self.ready_queue.append(task)
        heapq.heappush(self.ready_queue, task)
        if not self.cpu_busy:
            self.start_next_task()

    def handle_complete(self, task):
        print(f"[{self.clock}] Task {task.task_id} completed.")
        self.cpu_busy = False
        self.completed_tasks.append(task)
        self.start_next_task()

    def start_next_task(self):
        if self.ready_queue:
            # task = self.ready_queue.pop(0)
            task = heapq.heappop(self.ready_queue)
            start_time = self.clock
            finish_time = self.clock + task.duration
            print(f"[{start_time}] Task {task.task_id} started (runs till {finish_time})")
            self.cpu_busy = True
            self.schedule_event(Event(finish_time, 'complete', task))

if __name__ == "__main__":
    task_list = [
        Task(task_id=1, arrival_time=0, duration=4, priority=2),
        Task(task_id=2, arrival_time=1, duration=10, priority=1),
        Task(task_id=3, arrival_time=5, duration=2, priority=5),
        Task(task_id=4, arrival_time=6, duration=2, priority=3),
    ]

    scheduler = Scheduler()

    for t in task_list:
        scheduler.add_task(t)

    scheduler.run()