Week 07 Notes for CS 3750 -- Fall 2000

• Take Roll.
• Announcement(s)
  • I'm handing back the Exams
  • Grades are posted in the web space.
  • I will assign program #1 soon.
  • I assigned homework #4
• Discuss Deadlock avoidance and the banker's algorithm
• Discuss chapter 6 material up to coverage of semaphores

• Take Roll.
• Announcement(s)
  • I posted the program #1 assignment: concurrent bubble sort.
• Read the programming assignment and we will discuss it next time.
• Examine the safety algorithm pseudo-code in file "bankersAlg". Note that the safety algorithm can be viewed as a test to see if the system will be deadlocked if all processes immediately request their current "needs."
• Look at the specifics of one safety check in file bankersAlgEg.
• Examine the banker's algorithm and note the role played by the safety algorithm.
• Discuss chapter 6 material up to coverage of semaphores
• Bakery Algorithm: Generalizes the 2-process critical section problem solution to n-processes.
• Hardware support allows simplifying the code for the solution to the n-process critical section problem: The solution using the Test-and-Set instruction.
• Semaphores improve the previous methods by making the user-code extremely simple and by using block/wakeup instead of busy waiting.
• Look at the way file semsFromTSL illustrates the implementation of counting semaphores. Understand how implementation of the atomic semaphore operations is another critical section problem which is solved by a previously-studied "software method." Notice how some busy-waiting is still involved in the implementation of semaphores, but only a small amount compared to what might occur if we used something like the Bakery Algorithm to wait to enter a long critical section of code.
• Go over the rest of the slides for chapter 6 quickly, making some points. What is the purpose of each new primitive?