Description
This program sorts strings using “enzymes”. An enzyme is a function that sorts
two consecutive characters. We define one enzyme per pair of consecutive
characters; these enzymes working together in parallel can sort the entire
string. We use pthreads to instantiate and parallelize the enzymes.
Unfortunately, this program doesn’t seem to be working correctly. That’s where
you come in.
Before you edit the code, read through it, and answer these questions:
1) Briefly explain why this application would be difficult to write using
multiple processes instead of threads.
2) What is the significance of ‘workperformed’? How is it used?
3) Explain exactly what is the type of ‘fp’ in the following declaration:
void *(*fp)(void *)
Part II
=======
Now, to fix the program:
1) The function run_enzyme() needs to be created. Please see the notes inside
enzyme.c.
2) The function ‘make_enzyme_threads’ has a memory bug. Fix this by simply
re-ordering the lines in this function. It is simple fix but may take a
while for you to find it.
3) The function ‘join_on_enzymes’ is incomplete. Read the relevant man pages
and figure out how the function is supposed to work. Then insert the
correct code snippets into ‘whatgoeshere’.
4) Your programming work can be considered complete when you have completed
the above and all of the tests pass.
Testing
——-
make test
./enzyme -test -f0 all
Running tests…
1.make ::pass
2.sort ::pass
3.pleasequit1 ::pass
4.pleasequit0 ::pass
5.swap1 ::pass
6.swap2 ::pass
7.swap3 ::pass
8.run_enzyme ::pass
9.join ::pass
10.cancel ::pass
You may also want to experiment with the cancel function –
./enzyme Cba
./enzyme CBA
Questions
=========
1) Why do we not detach any of the enzyme threads? Would the program function
if we detached the sleeper thread?
2) Why does the program use sched_yield? What happens if this is not used?
Will the swap counts always be identical?
3) Threads are cancelled if the string contains a ‘C’ e.g. “Cherub”.
Why do we not include cancelled threads when adding up the total number
of swaps?
4) What happens when a thread tries to join itself?
(You may need to create a test program to try this)
Does it deadlock? Or does it generate an error?
5) Briefly explain how the sleeper thread is implemented.
6) Briefly explain why PTHREAD_CANCEL_ASYNCHRONOUS is used in this assignment.
7) Briefly explain the bug in Part II, #2 above.