操作系统进程调度算法(Java 实现)

FCFS(First Come First Server，先来先服务)

这是最简单，最基本的算法，它的思想非常简单，就是按照进程到来的时间顺序，逐个分配 CPU 资源
优点：简单，方便
缺点：效率低，资源利用率低

/**  * CPU 占用情况  * 1: 空闲  * 0: 正被占用  */ static int CPU = 1; /**  * 等待队列长度  */ static final int MAXLEN = 10; /**  * 先来先服务算法  * @param processes  */ public static void FCFS(List<Process> processes){     int count = processes.size();     int time = 0;     int[] waitQueue = new int[MAXLEN];     int front = 0;int tail = 0;     int running = 0;     System.out.println("-------------FCFS算法-------------");     if (count <= 0){         System.out.println("无可用进程");         return;     }     while (count > 0){         System.out.print("第 " + time + " 秒: ");         for (int i = 0; i < processes.size(); i++){             if (processes.get(i).isAlive() && processes.get(i).getInTime() == time){                 System.out.print("进程 " + i + " 到来 ");                 waitQueue[tail] = i;                 tail = (tail+1) % MAXLEN;             }             if (processes.get(running).isAlive() && processes.get(running).getCount() == 0){                 System.out.print("进程 " + running + " 结束运行 ");                 processes.get(running).setAlive(false);                 processes.get(running).setEndTime(time);                 count--;                 CPU = 1;             }         }         if (CPU == 1 && front != tail){             running = waitQueue[front];             front = (front+1) % MAXLEN;             System.out.print("进程 " + running + " 开始运行");             int temp = processes.get(running).getCount();             temp--;             processes.get(running).setCount(temp);             CPU = 0;         } else if (CPU == 0){             int temp = processes.get(running).getCount();             temp--;             processes.get(running).setCount(temp);         }         time++;         System.out.println();     }     System.out.println("---------------------------------");     ShowResult(processes); }

SJF(Short Job First，短作业优先)

按照进程预计需要的运行时间，按照从小到大分配资源
优点：简单进程执行速度快
缺点：无法准确预估运行时间，容易造成长进程饥饿

/** * 短作业优先算法 * 就是在 FCFS 算法中加入对 waitQueue 等待队列按照运行时间排序 *///改变部分...for (int i = 0; i < processes.size(); i++){    if (processes.get(i).isAlive() && processes.get(i).getInTime() == time){        System.out.print("进程 " + i + " 到来 ");        waitQueue[tail] = i;        tail = (tail+1) % MAXLEN;        length++;        /**         * 对等待队列按进程运行时长按从小到大排序         */        for (int x=front, z=0; z < length; x=(x+1)%MAXLEN, z++){            for (int y=x+1, q=0; q < length-x; y=(y+1)%MAXLEN, q++){                if (processes.get(waitQueue[x]).getCount() > processes.get(waitQueue[y]).getCount()){                    int t = waitQueue[x];                    waitQueue[x] = waitQueue[y];                    waitQueue[y] = t;                }            }        }    }...

PSA(优先级调度)

按照进程的优先级选择调度顺序

/** * 优先级调度算法 * 就是将 SJF 算法中的排序，改为按照优先级排序 *//** * 改变部分 * 对等待队列按进程优先级按从小到大排序 */for (int x=front, z=0; z < length; x=(x+1)%MAXLEN, z++){    for (int y=x+1, q=0; q < length-x; y=(y+1)%MAXLEN, q++){        if (processes.get(waitQueue[x]).getPriority() > processes.get(waitQueue[y]).getPriority()){            int t = waitQueue[x];            waitQueue[x] = waitQueue[y];            waitQueue[y] = t;        }    }}

RR (时间片轮转算法)

为 CPU 的执行设定一个时间片大小，每个进程轮询分配时间片，时间片结束后暂停运行加入等待队列

  /**   * 时间片轮转算法   * @param processes   * @param round   */  public static void RR(List<Process> processes, int round){      int count = processes.size();      int time = 0;      int[] waitQueue = new int[MAXLEN];      int front = 0;int tail = 0;      int running = 0;      System.out.println("------------- RR 算法-------------");      if (count <= 0){          System.out.println("无可用进程");          return;      }      while (count > 0){          System.out.print("第 " + time + " 秒: ");          for (int i = 0; i < processes.size(); i++){              if (processes.get(i).isAlive() && processes.get(i).getInTime() == time){                  System.out.print("进程 " + i + " 到来 ");                  waitQueue[tail] = i;                  tail = (tail+1) % MAXLEN;              }              if (processes.get(running).isAlive() && processes.get(running).getCount() == 0){                  System.out.print("进程 " + running + " 结束运行 ");                  processes.get(running).setAlive(false);                  processes.get(running).setEndTime(time);                  count--;                  CPU = 1;              }          }          if (CPU == 1 && front != tail){              running = waitQueue[front];              front = (front+1) % MAXLEN;              System.out.print("进程 " + running + " 开始运行");              int temp = processes.get(running).getCount();              temp--;              processes.get(running).setCount(temp);              CPU = 0;          } else if (CPU == 0){              int temp = processes.get(running).getCount();              temp--;              processes.get(running).setCount(temp);              if (time % round == 0){                  System.out.print("进程 " + running + " 暂停运行");                  waitQueue[tail] = running;                  tail = (tail+1) % MAXLEN;                  CPU = 1;              }          }          time++;          System.out.println();      }      System.out.println("---------------------------------");      ShowResult(processes);  }

算法运行结果显示

    /**     * 输出时间统计结果     * @param processes     */    public static void ShowResult(List<Process> processes){        int averageTime = 0;        for (int i = 0; i < processes.size(); i++){            int inTime = processes.get(i).getInTime();            int endTime = processes.get(i).getEndTime();            averageTime += endTime-inTime;            System.out.println("进程 " + i + " : 到来时间: " +                    inTime + " 结束时间: " +                    endTime + " 周转时间: " +                    (endTime-inTime));        }        System.out.println("平均周转时间: " + averageTime / processes.size());        System.out.println("---------------END--------------");    }