CMPUT 379 Written Assignment

CMPUT379--Operating System Concepts

Assignment I
Winter 2001

Due Date: Monday February 12, 2001

Submit your solutions to the instructor (in class) in printed form (hand written answers are not acceptable)--with the exception of neat, hand-drawn diagrams, if any. A print-out of a text file (properly formatted and with 2 cm margins) is acceptable, but a nice presentation (using a standard documentation tool) will make your work easier to read and mark.

Concise well-written answers are expected. A good source of background material is the first six chapters of your text by Silberschatz and Galvin, and your recent laboratory exercises.

1. What two advantages do threads have over multiple processes? What major disadvantage do they have? Suggest one application that would benefit from the use of threads, and one that would not. Explain why.

2. As presented in Section 4.4 of the text, the Pascal-like pseudo code there uses a maximum of N-1 of the available N buffers. Convert that to C-style pseudo code AND do so in such a way that now all N buffers can be correctly used. Build a solution that handles the general case (K-producers, M-consumers), perhaps? The text considers only the case K=M=1, you should handle K>=1 and M>=1.

Declare and initialize all variables and semaphores you use. Show the details of buffer index incrementation. Your answer must include specification of P()/V() synchronization primitives for a binary semaphore [perhaps using busy waiting], and wait()/free() primitives for a counting semaphore. Use these primitives appropriately to protect all shared resources and shared variables you use.

3. Provide simple busy-wait P() and V() synchronization primitives in C-pseudo code. Use them to solve the "Burger-Maker Problem". Common ingredients in a burger are: a pattie, a bun and cheese. Consider a system with three "dispenser" processes sitting at a conveyor; one has a supply of patties, one a supply of buns and one a supply of cheese. A fourth process, the cook, has a supply of all three and places any two different ingredients, selected randomly, on the conveyor. The dispenser with the missing third ingredient then completes the burger. Assuming that all supplies of pattie, bun and cheese are limitless, write C-pseudo code to implement and synchronize the activities of the cook and the dispensers. Be sure that only the dispenser who is currently garnishing and wrapping the burger signals to the cook to produce more ingredients. Here the cook is the"producer" and the dispensers are "consumers" in the classic producer/consumer problem sense.

4. Write a working C-program that accepts an arbitrary number of input lines of arbitrary length. Every line will contain Unix commands, each separated by a semicolon. As each line is read it is passed to a child process. That child process in turn creates as many children as necessary to execute concurrently all the Unix commands in the line. For example, an input line might be "date;ls -dg *;sleep 100;ps -aux". In this case the parent will create a child to accept the line and in turn create four children of its own to process the commands. Comment your program appropriately.

Submit a listing of your program, written as elegantly as you can. Describe the design issues you faced and how you addressed them. Show output from several test suites, enough to demonstrate the correctness and robustness of your program. Emphasise your attempts to find command sequences that break your program. Document your findings.