Mohammad’s Unreliable Guide to Exam 2

This is heavily based on Buffalo’s guide for Exam 2 from previous quarters, modified a bit to reflect some changes for this quarter.

| Last Modified | Winter 22-23 | | :———— | ———— |

Exam Format and Structure

This exam will be a timed take home exam where you will have to choose a 3 hours block of time to take the exam anywhere that is most convenient to you. Similar to Exam 1, you will be asked to clone a password-protected git repository. You will get the password from Moodle when you open the submission box.

Please note that once you complete the exam, you should submit your code to BOTH Moodle and Gradescope. It would make our life a lot easier to grade if we have access to your code in both places. If you skip submitting to gradescope, you risk us not seeing your solution.

In general, there will be 4 problems in this exam:

3 condition variables problems worth 70 points.
1 thread creation problem worth 30 points. This problem might be split into two parts if needed.

At the end of the exam, you should submit all of the .c files that you have changed. Feel free to include your thought process in comments in the code to help us better understand your approach and give you partial credit whenever applicable.

General Remarks

Time management is part of the exam, so keep an eye on your time.
The problem should generally be independent though of varying difficulty. Feel free to attempt a different problem if you get stuck on a particular one.
Keep backups of your code. If you have a partially working solution and would like to attempt something new, it might be worth it to backup the old one before making new changes.
Think in terms of patterns, and try to remember if we solved something similar in class. You have full access to the course website and any code that we have solved together in class.
It helps me personally to imagine a real-world analogy of the concurrency problem I am trying to solve. I tend to ask myself questions like: “If I were to solve this problem in real-life, how would I organize things?”

A Note on External Resources

Generally, problems you will have to solve are novel so Googling them is not a good idea as it often can be misleading. If you have questions, your instructor and the guidance sheet are your best source of information.
[New in 2023] I know that you might be tempted to use ChatGPT to solve your problem. My advice is simply to stay away from it. Here is my reasoning:
- The goal of you taking the class is to learn how to think about these kinds of problems, and not actually to just write a solution. You are not being tested on whether you can use the Internet (or the AI or whatever) to copy and paste a solution.
- You are doing yourself a disservice on the long term. Being an engineer is about problem solving and not about solution copying.
- I did experiment with ChatGPT a bit and so far, it has been 0/4 on the concurrency problems I have asked it to solve. So even if it spits out a solution, there are no guarantees that it will actually work.
- Finally, it is generally very easy for us to tell whether you really understand your attempted solution (even if it doesn’t work) compared to when you just copy it from somewhere else.

Required Skills

Thread Creation

You will be asked to parallelize a sequential program by creating threads at the appropriate time, and joining them.
Remember how you can pass parameters to the threads:
- Thread functions accept void * arguments, so pretty much you can pass anything in there assuming you properly cast it afterwards.
- If you need more than one argument, you can use a struct.
Recall what we talked about in class. The iterator variable in a for loop will disappear after the loop terminates, similarly for variables created inside the body of the loop, so passing those as parameters to thread functions is a pretty bad idea.
If you need synchronization at this point, a mutex lock is often enough, but a condition variable might be needed.

Exam 2 Preparation