Cohort 23 CS Online Journal

CST370 - Week 1 New course! CST370 is Design & Analysis of Algorithms.  Currently, I am wracking my brain trying to remember C++. It's been a while, but I feel more comfortable working with it versus Java.  From what I've read, using pseudocode is the most fundamental way to begin thinking about making programs. Before even translating it to a language, try to walk through the algorithm in your head or on paper. If you find that the algorithm is frustrating to make sense of already, how do you even begin implementing it in code? (Well, you still can, but understanding how it works is why we're here.)  I remember one of the hardest concepts for me to grasp was binary tree traversal. I hope I get a lot more practice out of it in this class!

Ooops. Forgot to update these.      Since I last made a blog post, I learned a great deal more about computer science. I am way more interested in web development, and had a great opportunity working with Eat for the Earth to create a better website. For my capstone project, I am more interested in making a web app resource for my TTRPG, to make it more accessible and easier to parse its content. Tentatively, the name of it is "Monstery Manual", because my TTRPG is called Monstery Dungeon. Might not do well with SEO using that name, so I will come up with a better name later. If you're familiar with Draw Steel's online resource Forge Steel, or LANCER RPG's online resource COMP/CON, it will be very similar to those and draw much of its design inspirations from them.      CST462S was very informative by teaching students how to work in a professional environment. The experience was a lot more laid-back than I expected, but might be because I worked with a non...

Week 7 Reflection This week, we covered a lot about persistence, and how the OS interacts with files, directories, and I/O devices.  I/O devices can range from memory buses to hard drives to keyboards. For a canonical I/O device, the canonical protocol is: While (STATUS == BUSY) ; // wait until device is not busy (polling the device) Write data to DATA register Write command to COMMAND register (Doing so starts the device and executes the command) While (STATUS == BUSY) ; // wait until device is done with your request  The basic protocol to interact with an IDE disk is: Wait for drive to be ready (polling). Write parameters to command registers. Start the I/O. Data transfer. Handle interrupts. Error handling. I/O time, or T I/O , is calculated by the seek delay + rotational delay + transfer delay. In other words,  T I/O  = T seek  +  T rotation +  T transfer The rate of I/O is the size of the transfer divided by the I/O time, or Size transfer  /...

Week 6 Reflection This week, we learned more about semaphores, and the bugs that are commonly faced in concurrency, such as deadlocks.  Semaphores are a synchronization primitive that has a modifiable integer value. The behavior of the semaphore is determined by this value. They can be used as both locks and condition variables for concurrency.  sem_wait() and sem_post() are used to interact with a semaphore. sem_wait() waits for a condition to be met, while sem_post() increments the value of the semaphore, then wakes a waiting thread. If a semaphore's value is negative, this number is equal to the number of waiting threads. For example, -4 equals four waiting threads, incrementing by 1 will change it to -3, waking one thread and now resulting in three waiting threads. Concurrency creates bugs that are difficult or costly to fix correctly. Non-deadlock bugs include atomicity violations and order violations. Atomicity violations occur when instructions that sho...

Week 5 Reflection      In this week, I learned a great deal about concurrency, threads, and best practices on how to keep threads managed efficiently. A thread is seen as a process that can share the same address space as another thread, and access the same data, rather than needing to occupy a different address space. Multi-threading is handling multiple threads in the same address space using thread control blocks (TCBs) to store thread states. For multi-threaded processes, each thread has its own stack, called the thread-local storage.       In the aside, four key terms are highlighted:  critical section: Code that accesses a shared resource, like a data structure or variable.  race condition (aka data race): If multiple threads enter the critical section at the same time, a race condition occurs. These threads could be executed in any order, leading to the program becoming indeterminate. indeterminate program: A program with one or more r...

Week 4 Reflection Paging - Virtual address --> Physical address Find the VPN bits (first X bits of a virtual address). Find the offset bits of the virtual address, which are the last Y bits (or, the virtual address with leading VPN bits removed). Find the corresponding PTE (if available). If the most significant bit (MSB) is a 1, it is a valid address. If 0, it is not valid and a physical address cannot be obtained from this virtual address. Find the PFN, which is the last Y bits of the PTE. If one is not listed, the number of pages a physical address can hold determines the PFN bits using the formula: [log2(number of pages)]. Then, combine the PFN and offset in this order to obtain the translated physical address. Swapping Swapping makes use of a few policies to determine what pages to swap in memory: The optimal policy (aka Belady or MIN) replaces pages that are accessed furthest in the future to maximize cache hit rates. This is not very practical because implementing pr...