Project #3 The scheduler

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BLG 335E Analysis of Algorithms I
Project #3
Problem Definition
The scheduler is a component of the operating system of our computers. As its name suggests, it schedules, or
alternates the resources provided to processes. The scheduler gives permission and resources for a particular
process to run. Then, depending on the structure of the underlying algorithm, it may preempt, or take
away that resource and provide it to another process. One of the most dangerous things that can happen
when scheduling multiple processes to take turns using particular CPU resources is deadlock. A deadlock
occurs when processes are holding onto resources such that there are not enough resources for any of them
to continue. Each process waits for the others to finish, causing an issue called starvation.
In the literature, there are many algorithms that are designed to prevent deadlock. One particular
algorithm is the Completely Fair Scheduler (CFS). CFS keeps a virtual running time (time allotted for a
process to date) of each process and increments this running time by the amount of time that process was
given CPU privileges. The run time for a process can be expressed as a monotonically increasing running
V irtualRunningT ime = V irtualRunningT ime + AllocatedT ime
When a process arrives, its initial virtual run time is calculated. Inputs such as a nice value can act as
a multiplier for a particular process to receive more or less CPU time–depending on its priority. At each
scheduling point, newly arriving processes are added to a Red Black Tree. In order to choose a process to
run, CFS selects the process with the minimum virtual running time. The virtual running time of the process
is updated, and if the process has not run to completion, then it is inserted back into the tree to await its
turn. At the next scheduling point, the process with the minimum run time is selected again. Because the
minimum run times are incremented, the upcoming orders of processes are shuffled. Therefore, deadlocks
and starvation are avoided. For more information on CFS, check out the link provided1
A description of the expected implementation can be given as follows:
1. Processes will be read according to their arrival time and stored in an RBTree structure (RBTree rules
apply.) according to their vruntime. A special case is that processes may have the same vruntime. In
this case, the process that is read/arrived later is added to the right child of the current process.
2. Check for incoming processes. Add any to your RB-Tree that have an arrival time less than or equal
to the current CPU time.
3. If there is a running task, and its vruntime is greater than the minvruntime, then remove that and add
it back to the tree with its updated vruntime value.
4. If there is no task running currently, choose the task with the smallest vruntime on the tree. Remove
that task from the tree to give it CPU privileges.
5. Update the currently running task by incrementing its vruntime value. Check whether or not it should
stop running.
6. Repeat until the max allotted time for the simulation is finished, or all the processes have come to
Important Note: Any addition or deletion to/from the red-black tree should be followed by the appropriate fixup routine.
Page 1 of 5
BLG 335E Analysis of Algorithms I Homework #3
• The arrival time and run time required inputs are not timestamp values but rather integer value. You
are free to simulate time in an abstract form (simply run through with a loop)!
• Please make sure to implement all of your tree methods naively. That is, your code should be written
by you and you only.
• No use of STL is permitted.
Sample Cases
Your code should read the processes from a .txt file. The desired format for the input is given in Listing
1. The output format should be as provided in Listing 2.
Code Listing 1: Input File Format
1 NumProcesses SimulatorRunTime
2 ProcessID TimeOfArrival BurstTime
Code Listing 2: Output File Format
1 CurrTime, RunningTask, TaskVruntime, MinVruntime, RBTTraversal, TaskStatus
3 Scheduling finished in … ms.
4 x of y processes are completed.
5 The order of completion of the tasks: x-y-z
*Note that the RBTree status will be provided using inorder traversal.
An example input file is given in Fig. 1, and the related simulation is illustrated in Fig. 2. Your code is
expected to work correctly in any input scenario. Further examples for input and outputs are provided in
Listings 3-6.
Figure 1: Sample of processes file
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BLG 335E Analysis of Algorithms I Homework #3
RBTree Simulation
CPU_time: 0 1 2 3 4 5 6
Info: min_vruntime = 0 min_vruntime = 0 min_vruntime = 0 min_vruntime=1 min_vruntime=1 min_vruntime=1
P1_vruntime += 1 P2_vruntime += 1 P3_vruntime += 1 P3_vruntime += 1 P1_vruntime += 1 P2_vruntime += 1
P3 Completed! P1 Completed! P2 Completed!
All (3) processes are completed!
Figure 2: Simulation of RBTree-based CFS
Code Listing 3: Example Input-1
1 3 7
2 P1 1 2
3 P2 2 2
4 P3 2 2
Code Listing 4: Example Output-1
1 0,-,-,-,-,-,-
2 1,P1,0,0,P1:0-Black,Incomplete
3 2,P2,0,0,P2:0-Red;P3:0-Black;P1:1-Red,Incomplete
4 3,P3,0,0,P3:0-Red;P1:1-Black;P2:1-Red,Incomplete
5 4,P3,1,1,P3:1-Red;P1:1-Black;P2:1-Red,Complete
6 5,P1,1,1,P1:1-Black;P2:1-Red,Complete
7 6,P2,1,1,P2:1-Black,Completed
9 Scheduling finished in …ms.
10 3 of 3 processes are completed.
11 The order of completion of the tasks: P3-P1-P2
Code Listing 5: Example Input-2
1 3 5
2 P1 1 2
3 P2 2 2
4 P3 2 2
Code Listing 6: Example Output-2
1 0,-,-,-,-,-,-
2 1,P1,0,0,P1:0-Black,Incomplete
3 2,P2,0,0,P2:0-Red;P3:0-Black;P1:1-Red,Incomplete
4 3,P3,0,0,P3:0-Red;P1:1-Black;P2:1-Red,Incomplete
5 4,P3,1,1,P3:1-Red;P1:1-Black;P2:1-Red,Complete
7 Scheduling finished in …ms.
8 1 of 3 processes are completed.
9 The order of completion of the tasks: P3
Page 3 of 5
BLG 335E Analysis of Algorithms I Homework #3
• Your efficient C++ Implementation of CFS using RB Trees. [70 pts]
– Please write your code clearly.
– Provide detailed comments.
• Report detailing your implementation. [30 pts]
– We expect your report to be in your own words.
– We expect that you write clearly and proofread your work before submitting.
Report Structure
Please answer the following questions in your report. Make sure to use your own words. Write your
report in sections, and provide visuals when necessary.
• Section 1: Description of Code Explain briefly the data structures you’ve constructed. Discuss
the attributes and methods you’ve implemented. Provide pseudocodes of the methods in your implementation.
• Section 2: Complexity Analysis What is the piece-wise AND overall complexity of your implementation? Provide a detailed discussion and upper bounds.
• Section 3: Food For Thought Answer the following questions briefly.
– Can you think of any advantages of using the RB Tree as the underlying data structure?
– Is the CFS used anywhere in the real world?
– What is the maximum height of the RBTree with N processes? Upper bound T(N)=? Prove it.
Page 4 of 5
BLG 335E Analysis of Algorithms I Homework #3
Submission Rules
• You should write your code in C++ language and try to follow an object-oriented methodology
with well-chosen variables, methods, and class names and comments where necessary.
• You cannot use the C++ Standard Template Library (STL) algorithms. In addition, the use of
specialized STL containers like deque, queue or priority queue is not permitted, but the use of vector
or list is allowed.
• You can define multiple classes in a single cpp file or use multiple cpp files with header files.
• It is mandatory to include a MakeFile which makes your code compiled with the ”make all” command.
• Also, make sure that your code can be run on our Docker container in the form of ./homework3
[input file].
• If the code is not self-explanatory and does not include adequate comments, a point penalty of up to
20 points will be applied.
All the reports must be prepared in LaTeX platform. You can use the following template: Sample
• Hand-written reports will not be accepted. Also for pseudocodes, please prepare them properly, do not
copy and paste your exact C++ code that you used for your assignments.
• Do not share any code or text that can be submitted as a part of an assignment (discussing ideas is



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