Prerequisite: Round Robin Scheduling with arrival time as 0
Round robin scheduling algorithm is used to schedule process fairly each job a time slot or quantum and the interrupting the job if it is not completed by then the job come after the other job which are arrived in the quantum time that make these scheduling fairly
- Round robin is a cyclic nature starvation doesn’t occur
- Round robin is variant of first come, first scheduling
- No priority, special importance given to any process or task
- RR scheduling is also know as Time slicing scheduling
- Each process is served by Cpu for a fixed time so priority is same for each one
- Starvation is not occur because of cyclic nataure.
- The quantum time make the throughput depend on it.
- if we want to give some process take first than other we can’t do these.
|Process||Arrival Time||Burst Time|
Quantum time is 3 that mean each process is only executing for only 3 unit at a time.
How to compute these process request:-
- Take the process which occur first and start executing the process.(only for quantum time only)
- Check that is any other process is come. if the process come in between quantum time in which process is executing then add it to the Ready queue
- After quantum time check is any process in Ready queue if ready queue is empty continue process if not empty then and if current process is not complete then add it to the ready queue at last.
- Take the first process from ready queue and executing it (same rules)
- Repeat all above step form 2-5
- If the process is complete and the ready queue is empty then task is complete
After all these we get the three time which are:
- Completion Time: the time at which process is complete.
- Turn Around Time: total time the process exist in system.(completion time – arrival time).
- Waiting Time: total time the waiting for there complete execution.(turn around time – burst time ).
How to implement in programming language
1. Create two arrays of burst time res_b and of arrival time res_a and copy the value of the b and a array for calculate the remaining time.(b is burst time, a arrival time). 2. Create an another array for wt to store waiting time. 3. Initialize Time : t=0; 4. Keep traversing the all process while all process are not done. Do following for i'th process if it is not done yet. a- if res_a[i]<= q (quantum time :- q) 1. if res_b[i]>q a. t=t+q b. res_b[i]-=q; c. a[i]+=q; 2. else res_b[i]<=q(for last to execute) a. t=t+b[i]; b. wt[i]=t-b[i]-a[i]; c.res_b[i]=0; b- else res_a[i]<q 1. Initialize j=0 to number of process if a[j]<a[i] (compare is there any other process come before these process) 1. if res_b[j]>q a. t=t+q b. res_b[j]-=q; c. a[j]+=q; 2. else res_b[j]<=q a. t=t+b[j]; b. wt[j]=t-b[j]-a[j]; c.res_b[j]=0; 2. now we executing the i'th process 1. if res_b[i]>q a. t=t+q b. res_b[i]-=q; c. a[i]+=q; 2. else res_b[i]<=q a. t=t+b[i]; b. wt[i]=t-b[i]-a[i]; c.res_b[i]=0;
Below is the implementation of the above approach:
name ctime wtime p1 22 12 p2 15 11 p3 16 11 p4 9 6 Average waiting time is 10.0 Average compilation time is 15.5 Sequence is like that ->p1->p2->p3->p4->p1->p2->p3->p1->p1
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