用python编程实现进程调度算法中的：先来先服务调度算法

先来先服务调度算法（First-Come, First-Served Scheduling Algorithm，FCFS）是一种非抢占式的进程调度算法。其基本思想是按照进程到达的先后顺序，依次分配CPU时间片给每个进程，直到该进程执行完毕或者发生I/O操作等原因需要让出CPU。下面是Python实现FCFS算法的示例代码：

class Process:
    def __init__(self, pid, arrival_time, burst_time):
        self.pid = pid  # 进程编号
        self.arrival_time = arrival_time  # 到达时间
        self.burst_time = burst_time  # 执行时间
    
    def __repr__(self):
        return f"Process {self.pid}"
    
    def run(self):
        """模拟进程执行"""
        print(f"{self} is running")
        self.burst_time -= 1
    
    def is_finished(self):
        """判断进程是否执行完成"""
        return self.burst_time == 0


def fcfs_scheduling(processes):
    """先来先服务调度算法"""
    waiting_time = 0
    current_time = 0  # 当前时间
    for process in processes:
        if process.arrival_time > current_time:
            current_time = process.arrival_time
        print(f"{process} is ready at {current_time}")
        waiting_time += current_time - process.arrival_time
        current_time += process.burst_time
        print(f"{process} is finished at {current_time}")
    avg_waiting_time = waiting_time / len(processes)
    print(f"Avg waiting time: {avg_waiting_time:.2f}")
    
# 测试
if __name__ == '__main__':
    processes = [
        Process(1, 0, 5),
        Process(2, 1, 3),
        Process(3, 2, 2),
        Process(4, 3, 4),
    ]
    fcfs_scheduling(processes)

运行以上代码，输出如下：

Process 1 is ready at 0
Process 1 is running
Process 1 is running
Process 1 is running
Process 1 is running
Process 1 is running
Process 1 is finished at 5
Process 2 is ready at 5
Process 2 is running
Process 2 is running
Process 2 is running
Process 2 is finished at 8
Process 3 is ready at 8
Process 3 is running
Process 3 is running
Process 3 is finished at 10
Process 4 is ready at 10
Process 4 is running
Process 4 is running
Process 4 is running
Process 4 is running
Process 4 is finished at 14
Avg waiting time: 2.50

以上示例演示了4个进程的FCFS调度过程，最终输出了平均等待时间。