PA5

CST334 Project: Databases and concurrency!

Assignment Description

In this project we're going to do two things. First, we're going to make a database be thread-safe by adding in locks and condition variables. Second, we're going to make a webserver be multi-threaded and able to use the thread-safe database.

Your task

You'll be doing two things.

1. You will be writing a set of functions to implement read and write locks to make a database object threadsafe. These functions should use both locks and condition variables.
2. You will be converting a webserver from being single-thread to multi-threaded

Functions you'll be writing

In this assignment you'll be writing 5 functions. Note that these funtions are used through the rest of the code in student_code.c, and only these 5 should be changed.

void pass_to_client_handler(void* arg) {
  // todo: Convert this to run multi-threaded
  client_handler(arg);
}


void read_lock(PlayerDatabase* db) {
  // todo
}

void read_unlock(PlayerDatabase* db) {
  // todo
}

void write_lock(PlayerDatabase* db) {
  // todo
}

void write_unlock(PlayerDatabase* db) {
  // todo
}

Note: When you start some of the tests will already pass. These will continue to pass until you implement some of the assigned functions, and them beginning to fail is expected behavior.

Scoring

For this assignment, scoring works a little bit differently. Instead of being scored on the individual functions, I have implemented tests that will test parts of how you implement the functions. To accomplish thisI have implemented three sets of unit tests.

1. (40 points) unittests_locks.c: contains lock-related unit tests and will evaluate each of your functions to determine if they utilize locks to protect data
2. (20 points) unittests_conditions.c: contains conditional variable unit tests and sees whether your code is appropriately waiting and checking for these
3. (20 points) unittests_server.c: tests for whether you have correctly implemented threading, and performs end-to end tests

Testing your code

Please note, I added in a number of waits for this code to allow for more accurate testing. This means that unit tests can take much longer to run than on previous assignments. Please be patient and consider disabling tests that you aren't currently working on.

Getting started

Setting up this project is very similar to the previous programming assignments, so please check those out if you have questions!

What to submit

You'll be submitting only student_code.c and student_code.h. Any other files changed will be lost during the grading process.

Tips and Tricks

1. The tests for this assignment have built-in sleep functions that cause it to run for a long time (~10 minutes when I write this). While it should output . as it runs, showing it's still working, and timeout if something goes horribly run, if you are testing a single function it might help to disable some of the unit tests. For details on how to do this, check out some of the labs!
2. For the server tests, there is a variable defined at the time called NUM_PLAYS. Reducing this might give you a way to quickly test some stuff. Don't forget to increase it again after you're done!
3. If you are testing your code by directly running the unit_tests executable (e.g. by typing in ./unit_tests) you should make sure you include the -j1 flag. However, running make by itself should work much better!
   • If you don't use the -j1 flag you are likely to get an error about bind()!

Conclusion

Good luck!