CPU Scheduling Simulator
v1.0
DESGIN DOCUMENTATION
FOR
CPU SCHEDULING ALGORITHM
By Nghia Ngoc Phan
Summer 2005
Class: CS 440
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1.
Introduction
In order to make the computer more productive in multiprogramming, the
operating system needs to switch the CPU among processes. It must provides the
basic algorithm to determine which process is allowed to get the CPU at the
current time, and whether that process is allowed to finish its execution
comparing to other processes in the system. Therefore, CPU scheduling
algorithms such as First Come First Served (FCFS), Shortest Job First (SJF),
Shortest Remaining Job (SRJ), Round-Robin (RR), and Priority are among
possible solutions for multiprogrammed operating system. Students in operating
system class should be familiar with these algorithms and be able to analyze these
algorithms.
Usually, students manually compute the waiting times and
turnaround times of these algorithms to compare their performances.
Consequently, the computation is inefficient and prone to error.
2. Goals and Objective
The CPU Scheduling Simulator is an automation that provides efficient and
errorless computation of waiting times and turnaround times of FCFS, SJF, SRJ,
RR, and Priority. The system provides the students a clean and convenient way to
test their given data or do the analysis of the CPU scheduling algorithms
mentioned above.
3. Requirements
a. User’s Level:
i.
For the purpose of analysis, the system allows the user to specify
number of datasets and number of processes in each dataset.
ii.
For the purpose of testing, a user is allowed to enter the
information of processes in his/her dataset. For each process, the
following information can be entered by a user: arrival time,
burst time, and priority.
iii.
FCFS, SJF, SRJ, RR, and Priority can be computed, and output is
in appropriate format for readability.
b. System’s Level:
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i.
Graphical User Interfaces (GUIs) will be provided for user
friendly.
ii.
Temporary storage is provided for datasets
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iii.
Dataset has no size limit.
iv.
Each process has its own properties and functions.
v.
Data will be generated for non-users’ datasets with the following
constraints:
 0 <= Burst Time <= 20
 0 <= Arrival Time <= 20
 0 <= Priority <= 20
 Time quantum is a list of values 1, 2, and 3.
vi.
For each CPU scheduling algorithm, average waiting time and
average turnaround time will be computed for each and all
datasets.
vii.
System will catch and handle any errors caused by the system or
user.
4. Specifications
a. Processes Diagrams:
i.
Context Diagram
Student
CPU
Scheduling
Simulator
Faculty
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ii.
1st Level Data Flow Diagram (DFD)
User
Requests
(1)
Scheduler
(2)
Display Input
Form 1
Invokes
Previous
Datasets
Generates
Next
(3)
Display Input
Form 2
Previous
Next
(4)
Display
Selection Form
iii.
2nd Level DFD
Selects
Closes
Selects
Closes
(4)
Display
Selection From
Selects
Closes
Selects
Closes
Selects
Closes
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(5)
Implements
First Come
First Served
(FCFS)
Output
(6)
Implements
Shortest Job
First (SJF)
Output
(7)
Implements
Priority
Output
(8)
Implements
Shortest
Remaining
Job (SRJ)
Output
(9)
Implements
Round-Robin
(RR)
Output
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b. Modules Descriptions:
i.
MainClass.java
 This is the first class that will be called to run the system.
Method Summary
void
main(String[] args)
 Create an object of Scheduler class.
ii.
Scheduler.java
 This class are handling users’ input/selection and
generating datasets.
 Extends JFrame
 Implements ActionListener interface
Field Summary
int
Number_Of_Process
 Value will inputted by a user. This will tell the system how
many processes in each dataset that the system needs to
generate.
int
Number_Of_Set
 Value will inputted by a user. This will tell the system how
many datasets that the system needs to generate.
int [][] Array_Process_ID
 Use to store the IDs of processes in the datasets.
int [][] Array_Process_Burst_Time
 Use to store the burst times of processes in the datasets.
int [][] Array_Process_Priority
 Use to store the priority numbers of processes in the datasets.
int [][] Array_Process_Arrival_Time
 Use to store the arrival times of processes in the datasets.
Constructor Summary
Scheduler()
 Create frames, add components onto frames, and display first input form
for the user to input number of datasets and number of processes in each
dataset.
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Method Summary
WelcomeFrame_Add_Shared_Components()
void
 Add shared components such as menu bar, menu items,
buttons onto welcome frame, which is the first input form (See
Processes Diagrams)
void
InputFrame_Add_Shared_Components()
 Similar to WelcomeFrame_Add_Shared_Components().
void
SelectionFrame_Add_Shared_Components()
 Similar to WelcomeFrame_Add_Shared_Components().
void
actionPerformed(ActionEvent e)
 Handling events such as button clicked or menu item selected.
void
System_Generates_Data()
 Generates datasets which will be stored in the arrays of process
id, arrival time, burst time, and priority.
iii.
SchedulingAlgorithm.java
 This class will handle the implementations of the following
CPU scheduling algorithms:
a. FCFS
b. SJF
c. Priority
d. SRJ
e. RR
 Extends JFrame
 Implements ActionListener
Field Summary
ProcessQueue []
ProcessQueue []
ProcessQueue []
double []
double []
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WaitingQueue
 Array contains list of objects belong to
ProcessQueue class. Each element of an array is a
dataset in waiting state.
ReadyQueue
 Array contains list of objects belong to
ProcessQueue class. Each element of an array is a
dataset in ready state.
FinishQueue
 Array contains list of objects belong to
ProcessQueue class. Each element of an array is a
dataset in finished state.
QueueAverageWaitingTime
 Each member of an array is an average waiting
time of one dataset in the system.
QueueAverageTurnaroundTime
 Each member of an array is an average turnaround
time of one dataset in the system.
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int
TimeCounter
 Use to specify the terminate time of a process.
Constructor Summary
SchedulingAlgorithm(int Array_Process_ID[][],int
Array_Process_Burst_Time[][], int Array_Process_Priority[][], int
Array_Process_Arrival_Time[][])
 Create display frame and add components onto it.
 Create datasets and processes in each data set.
 Each dataset is an object of ProcessQueue class.
 Each process is an object or Process class.
Method Summary
ProcessQueue SortQueue(ProcessQueue p_queue, int sortID)
 Sorts a dataset bases on sortID.
 sortID = 1 refers to sorted by CPU Burst Time
 sortID = 2 refers to sorted by CPU Arrival Time
 sortID = 3 refers to sorted by CPU Priority
int []
SwapArrayElement(int [] array, int index1, int index2)
 Swap element at index1 with element at index 2 of an
array.
void
Implement_FCFS_SJF_Priority(int AlgorithmID)
 Implements and displays output of the following CPU
scheduling algorithm:
1. AlgorithmID = 1 implies implementation of First
Come First Served Algorithm
2. AlgorithmID = 2 implies implementation of Shortest
Job First Algorithm
3. AlgorithmID = 3 implies implementation of Priority
Algorithm
void
Implement_SRJ()
 Implements and displays output of SRJ.
void
Implement_RR(int [] TimeQuantum)
 Implements and displays output of RR with different
time quantum of an array TimeQuantum.
void
RestoreData()
 Restore original data of datasets.
void
DisplaySummary(String FooterStr)
 Displays summary data such as average waiting time
and average turnaround time of all datasets.
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iv.
Process.java
 Object of this class can store its id, burst time, arrival time,
priority and performs operations such as calculate arrival
time, calculate turnaround time, and etc. A process in the
dataset is an object of this class.
Field Summary
int
BurstTime
int
CurrentBurstTime
int
Priority
int
ArrivalTime
int
TurnaroundTime
int
WaitingTime
int
TerminatedTime
int
ProcessID
Constructor Summary
Process(int PID, int BTime, int P, int ATime)
 Initializes all variables.
Method Summary
int
GetBurstTime()
int
GetCurrentBurstTime()
int
GetPriority()
int
GetArrivalTime()
int
GetTurnaroundTime()
int
GetWaitingTime()
int
GetTerminatedTime()
int
GetProcessID()
void
setArrivalTime(int ATime)
void
SetCurrentBurstTime(int BTime)
void
SetTerminatedTime(int TTime)
void
CalculateTurnaroundTime()
void
CalculateWaitingTime()
v.
ProcessQueue.java
 A java class for queue ADT. It is an array-based
implementation.
 An object of this class is a dataset that contains a list of
processes used for the implementation of CPU scheduling
algorithms.
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Field Summary
int
first
int
last
int
size
int
capacity
Object [] ObjArray
Constructor Summary
ProcessQueue()
 Default contructor.
ProcessQueue(int capacityElement)
 Contructor with specified capacity of the queue.
Method Summary
int
GetCapacity()
 Return capacity of the the queue
int
GetSize()
 Return number of elements in the queue
boolean IsEmpty()
 Return true if the queue is empty. false otherwise.
Object Object GetFront()
 Inspect the element at the front of the queue.
 Return element at the front of the queue, if exception occurs,
return error message.
Object GetLast()
 Inspect the element at the end of the queue.
 Return element at the front of the queue, if exception occurs,
return error message.
void
EnQueue(Object element)
 Insert an element at the rear of the queue.
Object Object DeQueue()
 Remove and return the element at the front of the queue.
 If exception occurs, return error message.
int
getLast()
int
getFirst()
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