CSCI 4210 — Operating Systems

Simulation Project (document version 1.2)

CPU Scheduling Simulation

操作系统代写 This project is to be completed either individually or in a team of at most three students; we recommend that you use either…


  • This project is to be completed either individually or in a team of at most three students; we recommend that you use either Nooks or your own WebEx meeting spaces to collaborate with your teams
  • Beyond your team (or yourself if working alone), do not share your code; however, feel free to discuss the project content and your fifindings with one another on the Discussion Forum
  • To appease Submitty, you must use one of the following programming languages: C, C++, Java, or Python (and be sure you choose only one language for your entire implementation)
  • Given that your simulation results might not entirely match the expected output on Submitty, we will cap your auto-graded grade at 60 points but have more than 60 auto-graded points available in Submitty; this should help you avoid the need to handle unusual corner cases, which are not an important aspect of this project
  • As per usual, your code must successfully compile/run on Submitty, which uses Ubuntu v18.04.5 LTS 操作系统代写

  • If you use C or C++, your program must successfully compile via gcc or g++ with no warning messages when the -Wall (i.e., warn all) compiler option is used; we will also use -Werror, which will treat all warnings as critical errors; the gcc/g++ compiler is version 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04).
  • For source fifile naming conventions, be sure to use *.c for C and *.cpp for C++; in either case, you can also include *.h fifiles
  • If you use Java, name your main Java fifile, and note that the javac compiler is version 8 (javac 1.8.0_282); do not use the package directive
  • For Python, you must use python3, which is Python 3.6.9; be sure to name your main Python fifile
  • For Java and Python, be sure no warning messages or extraneous output occur during compilation/interpretation
  • Please “flflatten” all directory structures to a single directory of source fifiles
  • The write-up described on the last page is worth 40% (40 points) of your project grade

Project specififications

For your simulation project, you will implement a simulation of an operating system. The focus will be on processes, assumed to be resident in memory, waiting to use the CPU. Memory and the I/O subsystem will not be covered in depth in this project.

Conceptual design 操作系统代写

A process is defifined as a program in execution. For this assignment, processes are in one of the following three states, corresponding to the picture shown further below.

  • RUNNING: actively using the CPU and executing its instructions
  • READY: ready to use the CPU, i.e., ready to execute its CPU burst
  • WAITING: blocked on I/O or some other event

Processes in the READY state reside in a queue called the ready queue. This queue is ordered based on a confifigurable CPU scheduling algorithm. There are four algorithms that you are to implement: fifirst-come-fifirst-served (FCFS); shortest job fifirst (SJF); shortest remaining time (SRT); and round robin (RR).

All four of these algorithms will be simulated for the same set of processes, which will therefore support a comparative analysis of results. As such, when you run your program, all four algorithms are to be simulated in succession.

In general, when a process is in the READY state and reaches the front of the queue, once the CPU is free to accept the next process, the given process enters the RUNNING state and starts executing its CPU burst.

After each CPU burst is completed, if the process does not terminate, the process enters the WAITING state, waiting for an I/O operation to complete (e.g., waiting for data to be read in from a fifile). When the I/O operation completes, depending on the scheduling algorithm, the process either (1) returns to the READY state and is added to the ready queue or (2) preempts the currently running process and switches into the RUNNING state.

Note that preemptions occur only for the SRT and RR algorithms. Each algorithm is described in the lecture videos from February 23 (also summarized on the next page).

First-come-fifirst-served (FCFS) 操作系统代写

The FCFS algorithm is a non-preemptive algorithm in which processes simply line up in the ready queue, waiting to use the CPU. This is your baseline algorithm (and could be implemented as RR with an “infifinite” time slice).

Shortest job fifirst (SJF)

In SJF, processes are stored in the ready queue in order of priority based on their anticipated CPU burst times. More specififically, the process with the shortest CPU burst time will be selected as the next process executed by the CPU.

Shortest remaining time (SRT)

The SRT algorithm is a preemptive version of the SJF algorithm. In SRT, when a process arrives, before it enters the ready queue, if it has a CPU burst time that is less than the remaining time of the currently running process, a preemption occurs. When such a preemption occurs, the currently running process is added back to the ready queue.

Round robin (RR) 操作系统代写

The RR algorithm is essentially the FCFS algorithm with predefifined time slice tslice. Each process is given tslice amount of time to complete its CPU burst. If this time slice expires, the process is preempted and added to the end of the ready queue (though see the rradd parameter described below).

If a process completes its CPU burst before a time slice expiration, the next process on the ready queue is immediately context-switched in to use the CPU.

Skipping preemptions in RR

For your simulation, if a preemption occurs and there are no other processes on the ready queue, do not perform a context switch. For example, given process G is using the CPU and the ready queue is empty, if process G is preempted by a time slice expiration, do not context-switch process G back to the empty queue; instead, keep process G running with the CPU and do not count this as a context switch. In other words, when the time slice expires, check the queue to determine if a context switch should occur.

Simulation confifiguration

The key to designing a useful simulation is to provide a number of confifigurable parameters. This allows you to simulate and tune for a variety of scenarios, e.g., a large number of CPU-bound processes, diffffering average process interarrival times, multiple CPUs, etc. 操作系统代写

Therefore, defifine the following simulation parameters as tunable constants within your code, all of which will be given as command-line arguments:

  • argv[1]: Defifine n as the number of processes to simulate. Process IDs are assigned in alphabetical order A through Z. Therefore, at most you will have 26 processes to simulate.
  • argv[2]: We will use a random number generator to determine the interarrival times of CPU bursts. Since we can only generate pseudo-random numbers, this command-line argument, seed, serves as the seed for the random number generator. To ensure predictability and repeatability, use srand48() with this given seed before simulating each scheduling algorithm and drand48() to obtain the next value in the range [0.0, 1.0). For other languages, implement an equivalent 48-bit linear congruential generator, as described in the man page for these functions in C.1

  • argv[4]: For the exponential distribution, this command-line argument represents the upper bound for valid pseudo-random numbers. This threshold is used to avoid values far down the long tail of the exponential distribution. As an example, if this is set to 3000, all generated values above 3000 should be skipped. For cases in which this value is used in the ceiling function (see the next page), be sure the ceiling is still valid according to this upper bound. 操作系统代写

  • argv[5]: Defifine tcs as the time, in milliseconds, that it takes to perform a context switch. Remember that a context switch occurs each time a process leaves the CPU and is replaced by another process. Note that the fifirst half of the context switch time (i.e., t cs 2 ) is the time required to remove the given process from the CPU; the second half of the context switch time is the time required to bring the next process in to use the CPU. Therefore, expect tcs to be a positive even integer.
  • argv[6]: For the SJF and SRT algorithms, since we cannot know the actual CPU burst times beforehand, we will rely on estimates determined via exponential averaging. As such, this command-line argument is the constant α. And note that the initial guess for each process is τ0 = 1 λ . When calculating τ values, use the “ceiling” function for all calculations.
  • argv[7]: For the RR algorithm, defifine the time slice value, tslice, measured in milliseconds.
  • argv[8]: Also for the RR algorithm, defifine whether processes are added to the end or the beginning of the ready queue when they arrive or complete I/O. This optional command-line argument, rradd, is set to either BEGINNING or END, with END being the default behavior.

Pseudo-random numbers and predictability

A key aspect of this assignment is to compare the results of each of the simulated algorithms with one another given the same initial conditions, i.e., the same initial set of processes. To ensure each CPU scheduling algorithm is given the same set of processes, carefully follow the algorithm below to defifine the set of processes. This algorithm should be fully executed before applying any of the scheduling algorithms.

Assume you defifine your exponential distribution pseudo-random number generation function as next_exp(). For each of the n processes, in order A through Z: 操作系统代写

  1. Identify the initial process arrival time as the “flfloor” of the next random number in the sequence given by next_exp(); note that you could therefore have a 0 arrival time
  1. Identify the number of CPU bursts for the given process as the “ceiling” of the next random number generated from the uniform distribution (obtained via drand48()) multiplied by 100; you should obtain a random integer in the inclusive range [1, 100]
  1. For each of these CPU bursts, identify the CPU burst time and the I/O burst time as the “ceiling” of the next two random numbers in the sequence given by next_exp(); multiply the I/O burst time by 10 such that I/O burst time is generally an order of magnitude slower than CPU burst time; for the last CPU burst, do not generate an I/O burst time (since each process ends with a fifinal CPU burst)

After you simulate each scheduling algorithm, you must reset the simulation back to the initial set of processes and set your elapsed time back to zero. More specififically, you must re-seed your random number generator to ensure the same set of processes and interarrival times.

Note that there may be times during your simulation in which the simulated CPU is idle because all processes are busy performing I/O. Also, when all processes terminate, your simulation ends.

Handling “ties” 操作系统代写

If difffferent types of events occur at the same time, simulate these events in the following order:

(a) CPU burst completion; (b) I/O burst completions (i.e., back to the ready queue); and then

(c) new process arrivals.

Further, any “ties” that occur within one of these three categories are to be broken using process ID order. As an example, if processes Q and T happen to both fifinish with their I/O at the same time, process Q wins this “tie” (because Q is alphabetically before T) and is therefore added to the ready queue before process T.

Be sure you do not implement any additional logic for the I/O subsystem. In other words, there are no I/O queues to implement.


For each algorithm, count the number of preemptions and the number of context switches that occur. Further, measure CPU utilization by tracking CPU usage and CPU idle time.

For each CPU burst, measure CPU burst time (given), turnaround time, and wait time. These will be averaged together for each algorithm.

CPU burst time 操作系统代写

CPU burst times are randomly generated for each process that you simulate (see algorithm above).

CPU burst time is defifined as the amount of time a process is actually using the CPU. Therefore, this measure does not include context switch times.

Turnaround time

Turnaround times are to be measured for each process that you simulate. Turnaround time is defifined as the end-to-end time a process spends in executing a single CPU burst.

More specififically, this is measured from process arrival time through to when the CPU burst is completed and the process is switched out of the CPU. Therefore, this measure includes the second half of the initial context switch in and the fifirst half of the fifinal context switch out, as well as any other context switches that occur while the CPU burst is being completed (i.e., due to preemptions).

Wait time

Wait times are to be measured for each process that you simulate. Wait time is defifined as the amount of time a process spends waiting to use the CPU, which equates to the amount of time the given process is actually in the ready queue. Therefore, this measure does not include context switch times that the given process experiences (i.e., only measure the time the given process is actually in the ready queue).

More specififically, a process leaves the ready queue when it is switched into the CPU, which takes half of context switch time tcs. Likewise, a preempted process leaves the CPU and enters the ready queue after the fifirst half of tcs.

CPU utilization 操作系统代写

Measure CPU utilization by tracking how much time the CPU is actively running CPU bursts versus total simulation time.

Required terminal output

Your simulator should keep track of elapsed time t (measured in milliseconds), which is initially zero for each scheduling algorithm. As your simulation proceeds, t advances to each “interesting” event that occurs, displaying a specifific line of output that describes each event.

Your simulator must display results for each of the four algorithms you simulate. For each algorithm, display a summary of the “pseudo-randomly” generated processes (which should be the same for each algorithm), then the “interesting” events from time 0 through time 999, followed only by process termination events and the fifinal end-of-simulation event. (v1.1) See example output fifiles posted in Submitty.

Your simulator must display a line of output for each “interesting” event that occurs using the format shown below. Note that the contents of the ready queue are shown for each event.

time <t>ms: <event-details> [Q <queue-contents>]

And the “interesting” events are: 操作系统代写

  • Start of simulation
  • Process arrival
  • Process starts using the CPU
  • Process fifinishes using the CPU (i.e., completes a CPU burst)
  • Process has its τ value recalculated (i.e., after a CPU burst completion)
  • Process preemption
  • Process starts performing I/O
  • Process fifinishes performing I/O
  • Process terminates by fifinishing its last CPU burst
  • End of simulation

The “process arrival” event occurs every time a process arrives, i.e., based on the initial arrival time and when a process completes I/O. In other words, processes “arrive” within the subsystem that consists only of the CPU and the ready queue.

The “process preemption” event occurs every time a process is preempted by a time slice expiration (in RR) or by an arriving process (in SRT). When a preemption occurs, a context switch occurs (unless for RR there are no available processes in the ready queue).

Note that when your simulation ends, you must display that event as shown below.

time <t>ms: Simulator ended for <algorithm> [Q empty]

Be sure that you still include the process removal time (i.e., half the context switch time) for this last process.

Required output fifile 操作系统代写

In addition to the above output (which should be sent to stdout), generate an output fifile called simout.txt that contains statistics for each simulated algorithm. The fifile format is shown below (with # as a placeholder for actual numerical data). Round to exactly three digits after the decimal point for your averages.

Algorithm FCFS

-- average CPU burst time: #.### ms

-- average wait time: #.### ms

-- average turnaround time: #.### ms

-- total number of context switches: #

-- total number of preemptions: #

-- CPU utilization: #.###% <=== corrected v1.1

Algorithm SJF

-- average CPU burst time: #.### ms

-- average wait time: #.### ms

-- average turnaround time: #.### ms

-- total number of context switches: #

-- total number of preemptions: #

-- CPU utilization: #.###% <=== corrected v1.1

Algorithm SRT

-- average CPU burst time: #.### ms

-- average wait time: #.### ms

-- average turnaround time: #.### ms

-- total number of context switches: #

-- total number of preemptions: #

-- CPU utilization: #.###% <=== corrected v1.1

Algorithm RR

-- average CPU burst time: #.### ms

-- average wait time: #.### ms

-- average turnaround time: #.### ms

-- total number of context switches: #

-- total number of preemptions: #

-- CPU utilization: #.###% <=== corrected v1.1

Note that averages are averaged over all executed CPU bursts. Also note that to count the number of context switches, you should count the number of times a process starts using the CPU.

Error handling

If improper command-line arguments are given, report an error message to stderr and abort further program execution. In general, if an error is encountered, display a meaningful error message on stderr, then abort further program execution.

Error messages must be one line only and use the following format:

ERROR: <error-text-here>

Submission instructions 操作系统代写

To submit your assignment (and also perform fifinal testing of your code), please use Submitty.

Note that this assignment will be available on Submitty a minimum of three days before the due date. Please do not ask when Submitty will be available, as you should fifirst perform adequate testing on your own Ubuntu platform.

Relinquishing allocated resources

Be sure that all resources (e.g., dynamically allocated memory) are properly relinquished for whatever language/platform you use for this assignment. Sloppy programming will potentially lead to grading penalties. (Consider doing frequent code reviews with your teammates if working on a team.)

Analysis and write-up requirements

Each project submission must also include a write-up with additional analysis.

Please address the questions below by submitting a PDF fifile called project-analysis.pdf. Answer all questions below in no more than six pages, not including fifigures, data, etc.

  1. Of the four simulated algorithms, which algorithm is the “best” algorithm for CPU-bound processes? Which algorithm is best-suited for I/O-bound processes? Support your answer by citing specifific simulation results.  操作系统代写
  1. For the RR algorithm, how does changing rr_add from END to BEGINNING impact your results? Which approach is “better” here?
  1. For the SJF and SRT algorithms, how does changing from a non-preemptive algorithm to a preemptive algorithm impact your results?
  1. Describe at least three limitations of your simulation, in particular how the project specififications could be expanded to better model a real-world operating system.
  1. Describe a priority scheduling algorithm of your own design (i.e., how could you calculate priority?). What are its advantages and disadvantages? Support your answer by citing specifific simulation results.

To ensure your write-up is readable, please follow the following layout requirements:

  • Use a readable 11- or 12-point font
  • Use standard 1” margins
  • Double-space your document
  • At the top of each page, include each team member’s name and RCS ID (e.g., “David Goldschmidt <goldsd3>”)
  • Number each page at the bottom (for easier reference)
  • And number your fifigures starting at 1 (i.e., Figure 1, Figure 2, etc.); reference these in your text (e.g., “As shown in Figure 1, …”)

Be sure to proofread your work before submitting! And note that you should submit your PDF along with your code for your fifinal submission.