FCFS(First Come First Server，先來先服務)

這是最簡單，最基本的演算法，它的思想非常簡單，就是按照程序到來的時間順序，逐個分配 CPU 資源
優點：簡單，方便
缺點：效率低，資源利用率低

/**
  * CPU 佔用情況
  * 1: 空閒
  * 0: 正被佔用
  */
 static int CPU = 1;
 /**
  * 等待佇列長度
  */
 static final int MAXLEN = 10;

 /**
  * 先來先服務演算法
  * @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演算法-------------");
     if (count <= 0){
         System.out.println("無可用程序");
         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("程序 " + i + " 到來 ");
                 waitQueue[tail] = i;
                 tail = (tail+1
 
) % MAXLEN;
             }
             if (processes.get(running).isAlive() && processes.get(running).getCount() == 0){
                 System.out.print("程序 " + running + " 結束執行 ");
                 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("程序 " + running + " 開始執行");
             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，短作業優先)

按照程序預計需要的執行時間，按照從小到大分配資源
優點：簡單程序執行速度快
缺點：無法準確預估執行時間，容易造成長程序飢餓

/**
 * 短作業優先演算法
 * 就是在 FCFS 演算法中加入對 waitQueue 等待佇列按照執行時間排序
 */

//改變部分
...

for (int i = 0; i < processes.size(); i++){
    if (processes.get(i).isAlive() && processes.get(i).getInTime() == time){
        System.out.print("程序 " + i + " 到來 ");
        waitQueue[tail] = i;
        tail = (tail+1) % MAXLEN;
        length++;
        /**
         * 對等待佇列按程序執行時長按從小到大排序
         */
        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(優先順序排程)

按照程序的優先順序選擇排程順序

/**
 * 優先順序排程演算法
 * 就是將 SJF 演算法中的排序，改為按照優先順序排序
 */

/**
 * 改變部分
 * 對等待佇列按程序優先順序按從小到大排序
 */
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 (時間片輪轉演算法)

為 CPU 的執行設定一個時間片大小，每個程序輪詢分配時間片，時間片結束後暫停執行加入等待佇列

  /**
   * 時間片輪轉演算法
   * @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 演算法-------------");
      if (count <= 0){
          System.out.println("無可用程序");
          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("程序 " + i + " 到來 ");
                  waitQueue[tail] = i;
                  tail = (tail+1) % MAXLEN;
              }
              if (processes.get(running).isAlive() && processes.get(running).getCount() == 0){
                  System.out.print("程序 " + running + " 結束執行 ");
                  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("程序 " + running + " 開始執行");
              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("程序 " + running + " 暫停執行");
                  waitQueue[tail] = running;
                  tail = (tail+1) % MAXLEN;
                  CPU = 1;
              }
          }
          time++;
          System.out.println();
      }
      System.out.println("---------------------------------");
      ShowResult(processes);
  }

演算法執行結果顯示

    /**
     * 輸出時間統計結果
     * @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("程序 " + i + " : 到來時間: " +
                    inTime + " 結束時間: " +
                    endTime + " 週轉時間: " +
                    (endTime-inTime));
        }
        System.out.println("平均週轉時間: " + averageTime / processes.size());
        System.out.println("---------------END--------------");
    }