CST334 Week 6 Report

 Concurrency: Part II

This week, we learned a ton more about concurrency in operating systems. Notably, the main topic was semaphores, which are essentially an upgraded version of our previous basic locks and condition variables which we can use to improve system performance, especially in multi-threading applications. Our book specifically defines a semaphore as an object with an integer value that we can manipulate with two routines, which in the posix standard are sem_wait() and sem_post(). It is important to remember that the initival value of a semaphore defines its behavior, so it must first be initialized to some value. The first type of semaphore we studied is the binary semaphore, used as a lock. Next, we learned how to implement semaphores for ordering events in a concurrent program. These semaphores can be very useful to use when a thread which is waiting for a list to become non-empty, so it can delete an element from it. Specifically, the semaphore would signal when another thread has completed, in order for the waiting thread to awaken into action, much like how condition variables work. We also learned about the producer/consumer problems and dining philosopher problems as means to understand semaphores on a deeper level. Avoiding concurrency bugs, including deadlock, was very helpful especially since we may implement semaphores ourselves in the future.