Computer Science 330
Operating Systems

Spring 2012, Siena College

Lab 2: Programming Unix Processes and Threads in C
Due: 9:20 AM, Friday, February 3, 2012

This week, you will gain experience creating and managing processes and threads in our Unix environments.

You may work individually or with a partner on this lab assignment.

Running Class Examples

Run the class examples that used fork and POSIX threads in the following three environments to answer the questions that follow in a file answers.txt.

  1. A Linux system in the lab.
  2. The Linux system
  3. The FreeBSD system

Question 1: Show the output of ps on each system showing the both the parent and child processes of the forking program, along with the output of the program on each system. (2 points)

Question 2: Log into a Linux system in the lab other than the one where you are doing the work for this lab (in case this crashes the system), and run the forkbomb program. How many processes can you create before you either get an error message (or the system crashes)? We won't try this experiment now on the other systems, but I was able to create over 3000 processes on winterstorm before running into trouble and well over 23,000 (!) on appserver. (1 point)

Question 3: Draw a memory diagram showing all of the variables in existence in the pthreadhello example when both child threads are executing. (2 points)

A sample output of the what_shared program on the Mac as we saw in class is:

First, we create two threads to see better what context they share...
Set this_is_global=1000
Thread 1, pid 67582, addresses: &global: 10A8, &local: B5EFC
In Thread 1, incremented this_is_global=1001
Thread 2, pid 67582, addresses: &global: 10A8, &local: 280EFC
In Thread 2, incremented this_is_global=1002
After threads, this_is_global=1002

Now that the threads are done, let's call fork..
Before fork(), local_main=17, this_is_global=17
In parent, pid 67582: &global: 10A8, &local: 5FBFEF5C
In child, pid 67583: &global: 10A8, &local: 5FBFEF5C
Child set local_main=13, this_is_global=23
In parent, local_main=17, this_is_global=17

Question 4: Run the what_shared example in each of the environments and paste in your output. What important differences do you see in the output and what do these differences mean? (3 points)

On the Mac, we saw in class that the proctree_threads program could create a thread tree of height 10 without encountering any thread creation errors, but did encounter errors at height 11.

Question 5: What is the tallest tree you can create on each of the three environments before thread creation errors are reported? (1 point)

fork() Practice

Write the program for SG&G Programming Problem 3.14 on p. 134-135. Call your program forkfib.c. Include a Makefile that compiles this program into an executable called forkfib.


Adding POSIX Shared Memory

Read Section 3.5.1 of SG&G to learn about POSIX shared memory. Then write the program for Exercise 3.18 on p. 137-138 of SG&G. Call your program forkfibshared.c and include a Makefile that compiles this program into forkfibshared.

Once your program is working, add a call to sleep(2) (recall that "2" here refers to the manual section, not the argument to pass) to your program before you detach and free the shared memory segment. In a separate window, use the ipcs command to see that your shared memory segment is listed, and that it goes away when your program terminates. Save this output and include it in a file ipcs.out to be included in your submission.

Now Using POSIX Threads

Write the program for Exercise 4.17 on p. 168-169 of SG&G. Call your program pthreadfib.c and include a Makefile that compiles this program into pthreadfib.

Submission and Evaluation

This lab is graded out of 40 points.

To submit this lab, place all of the files that you are to turn in (and nothing else) into a directory, change to that directory, and create a "tar file" to submit using a command similar to:

tar cvf lab2.tar *.out *.txt *.c Makefile

This will create a file lab2.tar in your directory. Send this tar file as an attachment to jteresco AT by 9:20 AM, Friday, February 3, 2012.

Please include a meaningful subject line (something like "CS330 Lab 2 Submission") and use the exact filenames specified (for this lab and all semester) to make my job easier when gathering your submissions together for grading. You don't want to annoy your grader with misnamed or missing files just before he grades your assignment. Please do not include any additional files, such as emacs backup files, object files, or executable programs.

Grading Breakdown

answers.txt responses and 9 points
forkfib.c correctness 6 points
forkfib.c efficiency, style, and elegance 2 points
forkfib.c documentation 2 points
forkfibshared.c correctness 6 points
forkfibshared.c efficiency, style, and elegance 2 points
forkfibshared.c documentation 2 points
pthreadfib.c correctness 6 points
pthreadfib.c efficiency, style, and elegance 2 points
pthreadfib.c documentation 2 points
Makefile(s) to build executables 1 point