c语言实现完成单处理器系统中的进程调度，要求实现时间片轮转、优先数、最短进程优 先和最短剩余时间优先四种调度算法。实验具体包括：首先确定进程控制块的内容，进程控 制块的组成方式；然后完成进程创建原语和进程调度原语；最后编写主函数对所作工作进行 测试。 模拟程序只对你所设置的“虚拟 PCB”进行相应的调度模拟操作，即每发生“调度” 时，显示出当前运行进程的“进程标识符”、“优先数”、“剩余运行时间”等，而不需要对系 统中真正的 PCB 等数据进行修改。要求能够动态地随机生成新进程添加到就绪队列中。主要考虑三个问题：如何组织进程、如何创建进程和如何实现处理器调度。首先要设定进程控制块的内容。进程控制块 PCB 记录各个进程执 行时的情况。每个进程都要有一个唯一的标识符，用来标识进程的存在和区别于其他进程。可以用符号或编号实现，它必须是操作系统分配的。记录进程的基本情况，例如进程的状态、等待原因、进程程序存放位置、进程数据存放位置等等。实验中，因为进程没有数据和程序，仅使用模拟的进程控制块，所以这部分 内容仅包含进程状态。进程状态可假设只有就绪、运行、终止三种。现场信息记录各个寄存器的内容。管理信息记录进程管理和调度的信息。例如进程优先数、进程队列指针等

。以下是一个简单的实现，包括进程控制块的定义、进程创建和调度原语的实现以及四种调度算法的实现。

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define MAX_PROCESS_NUM 10 // 最大进程数
#define TIME_SLICE 3 // 时间片长度

// 进程状态
enum ProcessState {
    READY,
    RUNNING,
    TERMINATED
};

// 进程控制块
struct PCB {
    int pid; // 进程标识符
    enum ProcessState state; // 进程状态
    int priority; // 进程优先级
    int arrival_time; // 进程到达时间
    int remaining_time; // 进程剩余执行时间
};

// 就绪队列
struct PCB *ready_queue[MAX_PROCESS_NUM];
int ready_queue_size = 0;

// 当前运行进程
struct PCB *running_process = NULL;

// 进程标识符计数器
int pid_counter = 0;

// 随机生成进程
void generate_process() {
    // 进程数量已达到最大值，不再生成新进程
    if (ready_queue_size == MAX_PROCESS_NUM) {
        return;
    }

    // 生成新的进程控制块
    struct PCB *process = (struct PCB *) malloc(sizeof(struct PCB));
    process->pid = pid_counter++;
    process->state = READY;
    process->priority = rand() % 5; // 随机生成优先级
    process->arrival_time = rand() % 10; // 随机生成到达时间
    process->remaining_time = rand() % 10 + 1; // 随机生成剩余执行时间

    // 将新进程加入就绪队列
    ready_queue[ready_queue_size++] = process;
}

// 时间片轮转调度算法
void schedule_round_robin() {
    // 当前没有运行进程，从就绪队列中选取一个进程开始执行
    if (running_process == NULL) {
        if (ready_queue_size > 0) {
            running_process = ready_queue[0];
            running_process->state = RUNNING;
            printf("Running process %d (priority %d, remaining time %d)\n",
                   running_process->pid, running_process->priority, running_process->remaining_time);
            ready_queue_size--;
            for (int i = 0; i < ready_queue_size; i++) {
                ready_queue[i] = ready_queue[i + 1];
            }
            ready_queue[ready_queue_size] = NULL;
        }
    }
    // 当前有运行进程，时间片到期，将其放回就绪队列尾部
    else {
        running_process->remaining_time -= TIME_SLICE;
        if (running_process->remaining_time <= 0) {
            running_process->state = TERMINATED;
            printf("Terminating process %d\n", running_process->pid);
            free(running_process);
            running_process = NULL;
        }
        else {
            running_process->state = READY;
            printf("Putting process %d back to ready queue (priority %d, remaining time %d)\n",
                   running_process->pid, running_process->priority, running_process->remaining_time);
            ready_queue[ready_queue_size++] = running_process;
            running_process = NULL;
        }
    }
}

// 优先数调度算法
void schedule_priority() {
    // 从就绪队列中选取优先级最高的进程开始执行
    int highest_priority = -1;
    int highest_priority_index = -1;
    for (int i = 0; i < ready_queue_size; i++) {
        if (ready_queue[i]->priority > highest_priority) {
            highest_priority = ready_queue[i]->priority;
            highest_priority_index = i;
        }
    }
    if (highest_priority_index != -1) {
        running_process = ready_queue[highest_priority_index];
        running_process->state = RUNNING;
        printf("Running process %d (priority %d, remaining time %d)\n",
               running_process->pid, running_process->priority, running_process->remaining_time);
        ready_queue_size--;
        for (int i = highest_priority_index; i < ready_queue_size; i++) {
            ready_queue[i] = ready_queue[i + 1];
        }
        ready_queue[ready_queue_size] = NULL;
    }
}

// 最短进程优先调度算法
void schedule_shortest_job_first() {
    // 从就绪队列中选取需要执行时间最短的进程开始执行
    int shortest_time = 100000;
    int shortest_time_index = -1;
    for (int i = 0; i < ready_queue_size; i++) {
        if (ready_queue[i]->remaining_time < shortest_time) {
            shortest_time = ready_queue[i]->remaining_time;
            shortest_time_index = i;
        }
    }
    if (shortest_time_index != -1) {
        running_process = ready_queue[shortest_time_index];
        running_process->state = RUNNING;
        printf("Running process %d (priority %d, remaining time %d)\n",
               running_process->pid, running_process->priority, running_process->remaining_time);
        ready_queue_size--;
        for (int i = shortest_time_index; i < ready_queue_size; i++) {
            ready_queue[i] = ready_queue[i + 1];
        }
        ready_queue[ready_queue_size] = NULL;
    }
}

// 最短剩余时间优先调度算法
void schedule_shortest_remaining_time_first() {
    // 从就绪队列中选取需要执行时间最短的进程开始执行
    int shortest_time = 100000;
    int shortest_time_index = -1;
    for (int i = 0; i < ready_queue_size; i++) {
        if (ready_queue[i]->remaining_time < shortest_time) {
            shortest_time = ready_queue[i]->remaining_time;
            shortest_time_index = i;
        }
    }
    if (shortest_time_index != -1) {
        // 如果当前没有运行进程，或者运行进程的剩余执行时间比被选中的进程剩余执行时间多，
        // 则将被选中的进程作为当前运行进程，否则将其放回就绪队列尾部
        if (running_process == NULL || running_process->remaining_time > shortest_time) {
            if (running_process != NULL) {
                running_process->state = READY;
                printf("Putting process %d back to ready queue (priority %d, remaining time %d)\n",
                       running_process->pid, running_process->priority, running_process->remaining_time);
                ready_queue[ready_queue_size++] = running_process;
            }
            running_process = ready_queue[shortest_time_index];
            running_process->state = RUNNING;
            printf("Running process %d (priority %d, remaining time %d)\n",
                   running_process->pid, running_process->priority, running_process->remaining_time);
            ready_queue_size--;
            for (int i = shortest_time_index; i < ready_queue_size; i++) {
                ready_queue[i] = ready_queue[i + 1];
            }
            ready_queue[ready_queue_size] = NULL;
        }
    }
}

// 主函数
int main() {
    srand(time(NULL));

    // 生成初始进程
    for (int i = 0; i < MAX_PROCESS_NUM / 2; i++) {
        generate_process();
    }

    // 模拟进程调度
    for (int i = 0; i < 20; i++) {
        printf("Time %d:\n", i);

        // 随机生成新进程
        if (rand() % 2 == 0) {
            generate_process();
        }

        // 执行调度算法
        //schedule_round_robin();
        //schedule_priority();
        //schedule_shortest_job_first();
        schedule_shortest_remaining_time_first();
    }

    return 0;
}

注意，这个实现仅是一个简单的示例，实际的操作系统中还需要考虑更多的因素，例如进程间的同步与通信、内存管理、文件系统等等。