Computer Science 225
Advanced Programming

Spring 2021, Siena College

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Agenda

• Announcements
  • lots going on!
  • Lab 8: Animation (in Canvas and GitHub)
    • not due until May 4 or 5 depending on your lab section
    • if you have finished the required functionality (as many have) and decide to go back to add some bonus functionality, be sure to let me know so I notice it
    • the threading and animation aspect of this lab is not fair game for the exam next week, but the code refactoring to add a common base class is
  • Problem Set 5
    • groups are formed, repositories created, now let's get it done
    • very good practice for the upcoming exam
  • Final Project
    • everyone should have been adding to the shared document for group formation and topic selection by now
    • groups need to be formed and repositories created by Monday
    • Proposals not due until Friday, but you are encouraged to get them in so I can check them sooner
  • Exam 2 - see the information/study guide shared document
• Finishing up the "windy" in-class excercise from last time
• Dangers of concurrency
• In-class exercise (5 points), create a Google document in your shared CSIS 225 folder for your response.
  1. Build a table that lists all of the possible interleavings of the instructions in the notes where Thread A and Thread B concurrently execute an increment and a decrement of the same variable counter.
  2. Suppose the counter variable starts at 0 before any of the statements are executed. Add a column to your table that gives the value of counter after the statements have been executed.
  3. Highlight the rows so that ones for which counter will have the correct final value (that is, the same as it was when we started) in green, and ones that give an incorrect answer in red.

Terminology

• interleaving of operations
• interference
• race condition
• process or thread synchronization

Examples

• ATMConcurrency