In this article, we are going to implement of Round Robin CPU Scheduling Algorithm (which is a preemptive version of FCFS algorithm) using C++ program. Submitted by Aleesha Ali, on February 06, 2018 This algorithm is the preemptive version of FCFS algorithm. Explanation:-Priority Scheduling Algorithm is a Non-Primitive algorithm most commonly used in Batch System, In this Type of system each process has Priority and according to Priority Process is executed By CPU and If Two process has same Priority then first come first serve to apply for executing the process.Higher Priority is executed first and so on and Priority of the process can be decided. Start exploring endless computing possibilities with your own Raspberry Pi computer and accessories.Perfect for beginners and students. Cpu scheduling program in c++ Life isn't about finding yourself. Life is about creating yourself. George Bernard Shaw Desire to have things done quickly prevents their being done thoroughly. Looking at small advantages prevents great affairs from being accomplished. Priority scheduling is necessarily a form of preemptive scheduling where priority is the basis of preemption. Problem with priority scheduling algorithm. 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.
- Priority Cpu Scheduling C Program
- Priority Based Scheduling
- Priority Cpu Scheduling Program In C
- Priority Scheduling Algorithm In C
- Operating System Tutorial
- OS - Exams Questions with Answers
- Operating System Useful Resources
- Selected Reading
A Process Scheduler schedules different processes to be assigned to the CPU based on particular scheduling algorithms. There are six popular process scheduling algorithms which we are going to discuss in this chapter −
- First-Come, First-Served (FCFS) Scheduling
- Shortest-Job-Next (SJN) Scheduling
- Priority Scheduling
- Shortest Remaining Time
- Round Robin(RR) Scheduling
- Multiple-Level Queues Scheduling
Priority Cpu Scheduling C Program
These algorithms are either non-preemptive or preemptive. Non-preemptivealgorithms are designed so that once a process enters the running state, it cannot be preempted until it completes its allotted time, whereas the preemptive scheduling is based on priority where a scheduler may preempt a low priority running process anytime when a high priority process enters into a ready state.
First Come First Serve (FCFS)
- Jobs are executed on first come, first serve basis.
- It is a non-preemptive, pre-emptive scheduling algorithm.
- Easy to understand and implement.
- Its implementation is based on FIFO queue.
- Poor in performance as average wait time is high.
Wait time of each process is as follows −
Process | Wait Time : Service Time - Arrival Time |
---|---|
P0 | 0 - 0 = 0 |
P1 | 5 - 1 = 4 |
P2 | 8 - 2 = 6 |
P3 | 16 - 3 = 13 |
![System System](/uploads/1/2/6/4/126482415/791432250.jpg)
Average Wait Time: (0+4+6+13) / 4 = 5.75
Shortest Job Next (SJN)
- This is also known as shortest job first, or SJF
- This is a non-preemptive, pre-emptive scheduling algorithm.
- Best approach to minimize waiting time.
- Easy to implement in Batch systems where required CPU time is known in advance.
- Impossible to implement in interactive systems where required CPU time is not known.
- The processer should know in advance how much time process will take.
Given: Table of processes, and their Arrival time, Execution time
Process | Arrival Time | Execution Time | Service Time |
---|---|---|---|
P0 | 0 | 5 | 0 |
P1 | 1 | 3 | 5 |
P2 | 2 | 8 | 14 |
P3 | 3 | 6 | 8 |
Waiting time of each process is as follows −
Process | Waiting Time |
---|---|
P0 | 0 - 0 = 0 |
P1 | 5 - 1 = 4 |
P2 | 14 - 2 = 12 |
P3 | 8 - 3 = 5 |
Average Wait Time: (0 + 4 + 12 + 5)/4 = 21 / 4 = 5.25
Priority Based Scheduling
- Priority scheduling is a non-preemptive algorithm and one of the most common scheduling algorithms in batch systems.
- Each process is assigned a priority. Process with highest priority is to be executed first and so on.
- Processes with same priority are executed on first come first served basis.
- Priority can be decided based on memory requirements, time requirements or any other resource requirement.
Given: Table of processes, and their Arrival time, Execution time, and priority. Here we are considering 1 is the lowest priority.
Process | Arrival Time | Execution Time | Priority | Service Time |
---|---|---|---|---|
P0 | 0 | 5 | 1 | 0 |
P1 | 1 | 3 | 2 | 11 |
P2 | 2 | 8 | 1 | 14 |
P3 | 3 | 6 | 3 | 5 |
Waiting time of each process is as follows −
Process | Waiting Time |
---|---|
P0 | 0 - 0 = 0 |
P1 | 11 - 1 = 10 |
P2 | 14 - 2 = 12 |
P3 | 5 - 3 = 2 |
Priority Based Scheduling
Average Wait Time: (0 + 10 + 12 + 2)/4 = 24 / 4 = 6
Shortest Remaining Time
Priority Cpu Scheduling Program In C
- Shortest remaining time (SRT) is the preemptive version of the SJN algorithm.
- The processor is allocated to the job closest to completion but it can be preempted by a newer ready job with shorter time to completion.
- Impossible to implement in interactive systems where required CPU time is not known.
- It is often used in batch environments where short jobs need to give preference.
Round Robin Scheduling
- Round Robin is the preemptive process scheduling algorithm.
- Each process is provided a fix time to execute, it is called a quantum.
- Once a process is executed for a given time period, it is preempted and other process executes for a given time period.
- Context switching is used to save states of preempted processes.
Wait time of each process is as follows −
Process | Wait Time : Service Time - Arrival Time |
---|---|
P0 | (0 - 0) + (12 - 3) = 9 |
P1 | (3 - 1) = 2 |
P2 | (6 - 2) + (14 - 9) + (20 - 17) = 12 |
P3 | (9 - 3) + (17 - 12) = 11 |
Average Wait Time: (9+2+12+11) / 4 = 8.5
Multiple-Level Queues Scheduling
Priority Scheduling Algorithm In C
Multiple-level queues are not an independent scheduling algorithm. They make use of other existing algorithms to group and schedule jobs with common characteristics.
- Multiple queues are maintained for processes with common characteristics.
- Each queue can have its own scheduling algorithms.
- Priorities are assigned to each queue.
For example, CPU-bound jobs can be scheduled in one queue and all I/O-bound jobs in another queue. The Process Scheduler then alternately selects jobs from each queue and assigns them to the CPU based on the algorithm assigned to the queue.