HW- 07 Solution

For this assignment we will honor those who have been married

(and divorced) multiple times. AKA If at first you don't succeed,

try, try again. Don't give up too easily; persistence pays off

in the end. The proverb has been traced back to 'Teacher's Manual'

by American educator Thomas H. Palmer and 'The Children of the

New Forest' by English novelist Frederick Maryat (1792-1848).

Originally a maxim used to encourage American schoolchildren

to do their homework. Palmer (1782-1861) wrote in his 'Teacher's

Manual': 'Tis a lesson you should heed, try, try again. If at

first you don't succeed, try, try again.' The saying was popularized

by Edward Hickson (1803-70) in his 'Moral Song' and is now applicable

to any kind of activity." From "Random House Dictionary of Popular

Proverbs and Sayings" by Gregory Y. Titelman (Random House, New York,

1996, Page 154).




PART 1:

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Create a set of 4 stand-alone programs, as follows:




Program #0 - Will always be called first and must create a set of

semaphores. Program #0 must print the exact text "Executing process

#0." when it runs. It must then terminate.




Program #1 - Will be started sometime after program #0 and must

adjust the semaphore(s) such that program #2 can run. Program #1

must print the exact text "Executing process #1." when it runs. It

must then terminate. Program #1 doesn't do anything else.




Program #2 - Will be started sometime after program #0 and must

adjust the semaphore(s) such that program #3 can run. Program #2

must print the exact text "Executing process #2." when it runs.

It must then terminate. Program #2 doesn't do anything else. However,

program #2 can only run AFTER program #1 runs! If program #2 runs

before program #1 it must simply terminate itself.




Program #3 - Will be started sometime after program #0 and should

remove the semaphores from the system. Program #3 must print the

exact text "Executing process #3." when it runs. It must then

terminate. Program #3 doesn't do anything else. However, program #3

can only run AFTER program #2 runs! If program #3 runs before program

#2 it must simply terminate itself.




PART 2:

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We will test your code using my program (a script) that will always

call program #0 first, but will call the remaining programs in all

possible permutations. Obviously, to get full credit only the correct

permutation should result in the following output:




Executing process #0.

Executing process #1.

Executing process #2.

Executing process #3.




SUGGESTIONS:

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See man pages for semget, semop, and semctl.




See man pages for errno and include errno.h - this will make things

much easier! You can use errno to troubleshoot your code and to help

determine how to tell when a process is attempted out-of-turn.




See my web site for a new file (errno.txt).




REQUIREMENTS:

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1. Your program must run on Linux Mint (Leonard 110/112).




2. Your full name must appear as a comment at the beginning of your

program.




3. Your programs MUST be named program0, program1, program2, and program3.

My script will assume those filenames. If your programs do not work because

you used different filename, you will get 0 points.




4. Your tarball must be named hw7-yourname.tar




5. Your program must use system V semaphores (semget, semop, and semctl).