Project 5S

Chapter 5 - Simulation

Download fork.py from the course website, and answer the following six questions from the end of Chapter 5 in the “Simulation” section. The readme file will be very useful as well.

Note: Write up your answers using whichever text editor you wish, but ultimately submit your answers as a pdf called project5s.pdf.

  1. Run fork.py -s 10 and see which actions are taken. Try to predict what the process tree looks like at each step. Use the -c flag to check your answers. Try a few different random seeds (using -s) or add more actions (using -a) to get the hang of it.

  2. One control the simulator gives you is the fork percentage, controlled by the -f flag. The higher it is, the more likely the next action is a fork; the lower it is, the more likely the action is an exit. Run the simulator with a large number of actions (e.g., -a 100) and vary the fork percentagefrom 0.1 to 0.9. What do you think the resulting final process trees will look like as the percentage changes? Check your answer with -c.

  3. Now, switch the output by using the -t flag (e.g., run fork.py -t). Given a set of process trees, can you tell which actions were taken?

  4. One interesting thing to note is what happens when a child exits; what happens to its children in the process tree? To study this, let’s create a specific example: fork.py -A a+b,b+c,c+d,c+e,c-. This example has process ‘a’ create ‘b’, which in turn creates ‘c’, which then creates ‘d’ and ‘e’. However, then, ‘c’ exits. What do you think the process tree should like after the exit? What if you use the -R flag? Learn more about what happens to orphaned processes on your own to add more context.

  5. One last flag to explore is the -F flag, which skips intermediate steps and only asks to fill in the final process tree. Run fork.py -F and see if you can write down the final tree by looking at the series of actions generated. Use different random seeds to try this a few times.

  6. Finally, use both -t and -F together. This shows the final process tree, but then asks you to fill in the actions that took place. By looking at the tree, can you determine the exact actions that took place? In which cases can you tell? In which can’t you tell? Try some different random seeds to delve into this question.