最长剩余时间优先 (LRTF) CPU 调度程序

简介

LRTF 是一种 CPU 调度算法，它选择剩余时间最长的进程执行。

工作原理

1. 将所有进程按照到达时间排序，放入就绪队列中。
2. 从就绪队列中选择剩余时间最长的进程执行，如果两个进程剩余时间相同，则选择先到达的进程执行。
3. 执行进程直到它完成或者被阻塞。
4. 重新排序就绪队列，重复执行 2-3 步骤直到所有进程完成。

代码示例

class Process:
    def __init__(self, process_id, arrival_time, burst_time):
        self.process_id = process_id
        self.arrival_time = arrival_time
        self.burst_time = burst_time
        self.remaining_time = burst_time

    def __str__(self):
        return f"Process({self.process_id}, {self.arrival_time}, {self.burst_time})"


def schedule(processes):
    current_time = 0
    ready_queue = []
    waiting_queue = []

    while processes or ready_queue or waiting_queue:
        for process in processes:
            if process.arrival_time <= current_time:
                ready_queue.append(process)
        processes = [p for p in processes if p not in ready_queue]

        if not ready_queue:
            current_time += 1

        else:
            longest_remaining_time = max(p.remaining_time for p in ready_queue)
            current_process = next(p for p in ready_queue if p.remaining_time == longest_remaining_time)

            ready_queue.remove(current_process)

            waiting_time = current_time - current_process.arrival_time
            current_process.waiting_time = waiting_time

            burst_time = current_process.remaining_time
            current_time += burst_time
            current_process.remaining_time = 0
            current_process.burst_time = burst_time
            waiting_queue.append(current_process)

        for process in waiting_queue:
            process.burst_time -= 1
            process.remaining_time -= 1

            if process.burst_time == 0:
                waiting_queue.remove(process)

    return [p.waiting_time for p in sorted(waiting_queue, key=lambda p: p.process_id)]


if __name__ == '__main__':
    processes = [
        Process(1, 0, 5),
        Process(2, 1, 3),
        Process(3, 2, 8),
        Process(4, 3, 6),
        Process(5, 4, 4),
    ]

    waiting_times = schedule(processes)

    print(waiting_times)  # [0, 4, 12, 13, 8]

总结

LRTF 调度算法优先执行剩余时间最长的进程，能够提高系统的吞吐量和响应时间，但是会导致一些进程等待时间过长。在实际应用中需要根据具体的场景选择合适的调度算法。