• 操作系统抢占式优先级调度Priority scheduling is a type of scheduling algorithm used by the operating system to schedule the processes for execution. The priority scheduling has both the preemptive mode...
操作系统抢占式优先级调度Priority scheduling is a type of scheduling algorithm used by the operating system to schedule the processes for execution. The priority scheduling has both the preemptive mode of scheduling and the non-preemptive mode of scheduling. Here, we will discuss the non-preemptive priority scheduling algorithm.
优先级调度是操作系统用来调度要执行的进程的调度算法。 优先级调度既有抢占式调度又有非抢占式调度。 在这里， 我们将讨论非抢占式优先级调度算法 。
As the name suggests, the scheduling depends upon the priority of the processes rather than its burst time. So, the processes, in this case, must also have the priority number in its details on the basis of which the OS will schedule it.
顾名思义，调度取决于进程的优先级，而不是突发时间。 因此，在这种情况下，进程还必须在其详细信息中具有优先级号，操作系统将根据该优先级号对其进行调度。
For example, suppose we have 4 processes: P1, P2, P3 and P4 and they enter the CPU as follows:
例如，假设我们有4个进程： P1 ， P2 ， P3和P4 ，它们按如下方式进入CPU：
Note: Here, lower the priority number, higher is the priority.
注意：此处，优先级数字越低，优先级越高。
As per the non-preemptive priority scheduling, the processes will be executed as follows:
根据非抢先优先级调度 ，将按以下方式执行过程：
Gant Chart:
甘特图：
Explanation:
说明：
There is only P1 available at time 0, so it will be executed first irrespective of the priority, and it cannot be preempted in between before its completion. 在时间0只有P1可用，因此无论优先级如何都将首先执行它，并且在完成之前不能抢占它。 When it is completed at 4th-time unit, we have all P2, P3, and P4 available. So, they are executed according to their priorities. 当以第 4 次单位完成时，我们将拥有所有P2 ， P3和P4 。 因此，将根据优先级执行它们。     Total Turn Around Time = 4 + 7 + 9 + 2
= 22 milliseconds
Average Turn Around Time= Total Turn Around Time / Total No. of Processes
= 22 / 4
= 5.5 milliseconds

Total Waiting Time = 0 + 5 + 6 + 0
= 11 milliseconds
Average Waiting Time = Total Waiting Time / Total No. of Processes
= 11 / 4
= 2.75 milliseconds


翻译自: https://www.includehelp.com/operating-systems/priority-scheduling-non-preemptive.aspx操作系统抢占式优先级调度
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• 操作系统抢占式优先级调度In the priority scheduling, the processes are scheduled on the basis of their priority, and not on the basis of their burst time. If the preemptive mode of this scheduling is ...
操作系统抢占式优先级调度In the priority scheduling, the processes are scheduled on the basis of their priority, and not on the basis of their burst time. If the preemptive mode of this scheduling is being followed, then a process with a higher priority than the currently executing process can replace the executing process. This can be well explained with the help of the following example:
在优先级调度中 ，将根据进程的优先级而不是根据突发时间来调度进程。 如果遵循此调度的抢占模式 ，则优先级高于当前正在执行的进程的进程可以替换正在执行的进程。 可以通过以下示例很好地解释这一点：
Suppose, we have four processes: P1, P2, P3 and P4, and they enter the CPU in the following manner:
假设我们有四个进程： P1 ， P2 ， P3和P4 ，它们以以下方式进入CPU：
As per the preemptive priority scheduling, the processes will be executed as follows:
根据抢先优先级调度 ，这些过程将按以下方式执行：
Gant Chart
甘特图
Explanation:
说明：
There is only P1 available at time 0, so it will be executed first irrespective of the priority until some other process with a higher priority is encountered by the OS. 在时间0只有P1可用，因此它将优先于优先级执行，直到OS遇到其他具有更高优先级的进程为止。 At the beginning of the 1st-time unit, we have P2 which has a higher priority than P1, so it replaces P1. 在第1 个 -时间单元的开始，我们有P2具有比P1更高的优先级，因此它取代P1。 At 2nd time unit, we have the process P3, but its priority is less than the executing process P2, so P2 keeps executing without any replacement. 在第二时间单位，我们有进程P3 ，但是它的优先级小于执行进程P2 ，因此P2继续执行而没有任何替换。 At 3rd time unit, our P2 has been completed and till now we have processes P1 and P3 left. So, P1 which has a higher priority than P3 is executed. 在第三个时间单元，我们的P2已完成，到现在为止，我们还有流程P1和P3 。 因此，执行优先级高于P3的 P1 。 At 4th time unit, we have process P4 which has the highest priority of them all. So, it replaces P1. 在第 4 个时间单位，我们有进程P4 ，它是所有进程中的最高优先级。 因此，它将替换P1 。 Since now we have no more processes left to arrive, the processes will now run according to their priorities and will complete their execution. 从现在开始，我们不再需要其他任何流程，这些流程将根据其优先级运行并完成其执行。     Total Turn-Around Time = 8 + 2 + 9 + 2
= 21 milliseconds
Average Turn-Around Time= Total Turn-Around Time / Total No. of Processes
= 21 / 4
= 5.25 milliseconds

Total Waiting Time = 4 + 0 + 6 + 0
= 10 milliseconds
Average Waiting Time = Total Waiting Time / Total No. of Processes
= 10 / 4
= 2.5 milliseconds


翻译自: https://www.includehelp.com/operating-systems/priority-scheduling-preemptive.aspx操作系统抢占式优先级调度
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• 某小型实时操作系统采用优先级进行调度，就绪表最多容纳32个任务，用4个元素的数组P表示就绪表，每个元素为一个字节，每个字节的一位表示该优先级的任务是否就绪。若P[0]=00100010,则表示优先级为1与优先级为5的任务...
• 优先级调度算法动态优先级We are already familiar with what Priority Scheduling is. It is one of the most used process scheduling algorithm used in operating systems, in which every process is assigned ...
优先级调度算法动态优先级We are already familiar with what Priority Scheduling is. It is one of the most used process scheduling algorithm used in operating systems, in which every process is assigned with a priority. According to this algorithm, the process with the highest priority is set to be provided the CPU first or simply is to be executed first.
我们已经熟悉什么是优先调度。 它是操作系统中使用最广泛的进程调度算法之一，在该算法中，每个进程都分配了优先级。 根据该算法，将优先级最高的过程设置为首先提供给CPU或简单地首先执行。
In priority scheduling algorithm, a major problem to be considered is the starvation of a process i.e. a process which is ready to be executed but is waiting for the CPU because of its low priority. This can lead to the indefinite waiting of the low-priority processes. A continuous flow of higher priority processes to the O.S can prevent a low priority process from ever getting the CPU.
在优先级调度算法中 ，要考虑的主要问题是进程的饥饿 ，即由于其低优先级而准备执行但正在等待CPU的进程。 这可能导致无限期等待低优先级进程。 高优先级进程不断流向OS可以防止低优先级进程获得CPU。
Let's take an example to understand what starvation is. Suppose there are 100 processes in which a process 'X' has the lowest priority because of which it will be executed at last. Let say before the process 'X' is provided CPU for the execution some more processes are provided to the operating system having a priority higher than that of process 'X'. Now what will happen is, the process 'X' won't get the chance to get executed no matter what was its arrival time. It is possible that, as the time passes by the O.S is given more processes having higher priority than that of 'X', due to which 'X' can wait indefinitely or could never be executed. This Problem is known as 'Starvation'.
让我们举一个例子来了解什么是饥饿 。 假设有100个进程，其中进程'X'具有最低优先级，因为它最终将被执行。 可以说，在为CPU提供进程“ X”以供执行之前，向操作系统提供的其他进程的优先级高于进程“ X”的优先级。 现在将要发生的是，无论到达时间是什么，进程“ X”都不会有执行的机会。 随着时间的流逝，可能会给OS提供更多比'X'具有更高优先级的进程，因此'X'可以无限期等待或无法执行。 这个问题被称为“饥饿” 。
For solving the problem of starvation we have the concept of Aging. In aging what we do is increasing the priority of those process that has been waiting long because of low priority after some specified amount of time. Due to which after the specified time its priority is increased and could be provided with the CPU for the execution.

为了解决饥饿问题，我们有老龄化的概念。 在老化中，我们要增加由于在指定的时间量后优先级较低而一直等待很久的那些进程的优先级。 因此，在指定的时间之后，其优先级会增加，并且可以随CPU提供以执行该优先级。
翻译自: https://www.includehelp.com/operating-systems/problem-associated-with-priority-scheduling-and-its-solution.aspx优先级调度算法动态优先级
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• 优先级调度算法c实现Here you will get C and C++ program for priority scheduling algorithm. 在这里，您将获得用于优先级调度算法的C和C ++程序。 What is Priority Scheduling Algorithm? 什么是优先级调度...
优先级调度算法c实现Here you will get C and C++ program for priority scheduling algorithm.
在这里，您将获得用于优先级调度算法的C和C ++程序。
What is Priority Scheduling Algorithm?
什么是优先级调度算法？
In priority scheduling algorithm each process has a priority associated with it and as each process hits the queue, it is stored in based on its priority so that process with higher priority are dealt with first. It should be noted that equal priority processes are scheduled in FCFS order.

Also Read: C Program for Shortest Job First (SJF) Scheduling Algorithm
在优先级调度算法中，每个进程都具有与之关联的优先级，并且当每个进程到达队列时，将根据其优先级将其存储在其中，以便优先处理优先级较高的进程。 应该注意的是，以FCFS顺序安排优先级相同的进程。
另请阅读： 最短作业优先(SJF)调度算法的C程序
C/C++ Program for First Come First Served (FCFS) Scheduling Algorithm用于先到先得(FCFS)调度算法的C / C ++程序To prevent high priority processes from running indefinitely the scheduler may decrease the priority of the currently running process at each clock tick (i.e., at each clock interrupt). If this action causes its priority to drop below that of the next highest process, a process switch occurs. Alternatively, each process may be assigned a maximum time quantum that it is allowed to run. When this quantum is used up, the next highest priority process is given a chance to run.
为了防止高优先级进程无限期地运行，调度程序可以在每个时钟滴答时(即，在每个时钟中断时)降低当前正在运行的进程的优先级。 如果此操作导致其优先级降低到下一个最高进程的优先级以下，则会发生进程切换。 替代地，可以为每个过程分配允许其运行的最大时间量。 当这个数量用完时，下一个优先级最高的进程将有机会运行。
局限性 (Limitations)The problem occurs when the operating system gives a particular task a very low priority, so it sits in the queue for a larger amount of time, not being dealt with by the CPU. If this process is something the user needs, there could be a very long wait, this process is known as “Starvation” or “Infinite Blocking”.
当操作系统为特定任务赋予非常低的优先级时，就会发生此问题，因此它会在队列中停留较长的时间，而不会由CPU处理。 如果用户需要此过程，则可能要等待很长时间，此过程称为“饥饿”或“无限阻止”。
解 (Solution)Many operating systems use a technique called “aging”, in which a low priority process slowly gains priority over time as it sits in the queue. Even if, the priority of the process is low, there is a surety of its execution.
许多操作系统使用一种称为“老化”的技术，其中低优先级的进程位于队列中时，它会随着时间的流逝逐渐获得优先级。 即使该进程的优先级较低，也可以肯定其 执行。
C程序 (C Program)
#include<stdio.h>

int main()
{
int bt[20],p[20],wt[20],tat[20],pr[20],i,j,n,total=0,pos,temp,avg_wt,avg_tat;
printf("Enter Total Number of Process:");
scanf("%d",&n);

printf("\nEnter Burst Time and Priority\n");
for(i=0;i<n;i++)
{
printf("\nP[%d]\n",i+1);
printf("Burst Time:");
scanf("%d",&bt[i]);
printf("Priority:");
scanf("%d",&pr[i]);
p[i]=i+1;           //contains process number
}

//sorting burst time, priority and process number in ascending order using selection sort
for(i=0;i<n;i++)
{
pos=i;
for(j=i+1;j<n;j++)
{
if(pr[j]<pr[pos])
pos=j;
}

temp=pr[i];
pr[i]=pr[pos];
pr[pos]=temp;

temp=bt[i];
bt[i]=bt[pos];
bt[pos]=temp;

temp=p[i];
p[i]=p[pos];
p[pos]=temp;
}

wt[0]=0;	//waiting time for first process is zero

//calculate waiting time
for(i=1;i<n;i++)
{
wt[i]=0;
for(j=0;j<i;j++)
wt[i]+=bt[j];

total+=wt[i];
}

avg_wt=total/n;      //average waiting time
total=0;

printf("\nProcess\t    Burst Time    \tWaiting Time\tTurnaround Time");
for(i=0;i<n;i++)
{
tat[i]=bt[i]+wt[i];     //calculate turnaround time
total+=tat[i];
printf("\nP[%d]\t\t  %d\t\t    %d\t\t\t%d",p[i],bt[i],wt[i],tat[i]);
}

avg_tat=total/n;     //average turnaround time
printf("\n\nAverage Waiting Time=%d",avg_wt);
printf("\nAverage Turnaround Time=%d\n",avg_tat);

return 0;
}
C ++程序 (C++ Program)
#include<iostream>

using namespace std;

int main()
{
int bt[20],p[20],wt[20],tat[20],pr[20],i,j,n,total=0,pos,temp,avg_wt,avg_tat;
cout<<"Enter Total Number of Process:";
cin>>n;

cout<<"\nEnter Burst Time and Priority\n";
for(i=0;i<n;i++)
{
cout<<"\nP["<<i+1<<"]\n";
cout<<"Burst Time:";
cin>>bt[i];
cout<<"Priority:";
cin>>pr[i];
p[i]=i+1;           //contains process number
}

//sorting burst time, priority and process number in ascending order using selection sort
for(i=0;i<n;i++)
{
pos=i;
for(j=i+1;j<n;j++)
{
if(pr[j]<pr[pos])
pos=j;
}

temp=pr[i];
pr[i]=pr[pos];
pr[pos]=temp;

temp=bt[i];
bt[i]=bt[pos];
bt[pos]=temp;

temp=p[i];
p[i]=p[pos];
p[pos]=temp;
}

wt[0]=0;            //waiting time for first process is zero

//calculate waiting time
for(i=1;i<n;i++)
{
wt[i]=0;
for(j=0;j<i;j++)
wt[i]+=bt[j];

total+=wt[i];
}

avg_wt=total/n;      //average waiting time
total=0;

cout<<"\nProcess\t    Burst Time    \tWaiting Time\tTurnaround Time";
for(i=0;i<n;i++)
{
tat[i]=bt[i]+wt[i];     //calculate turnaround time
total+=tat[i];
cout<<"\nP["<<p[i]<<"]\t\t  "<<bt[i]<<"\t\t    "<<wt[i]<<"\t\t\t"<<tat[i];
}

avg_tat=total/n;     //average turnaround time
cout<<"\n\nAverage Waiting Time="<<avg_wt;
cout<<"\nAverage Turnaround Time="<<avg_tat;

return 0;
}
Output
输出量
翻译自: https://www.thecrazyprogrammer.com/2014/11/c-cpp-program-for-priority-scheduling-algorithm.html优先级调度算法c实现
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