1. Slide design: Dr. Mark L. Hornick
SE3910
5/7/2019
SE3910 Week 9, Class 1
Week 9 Lab:
Individual demos of working sub-modules
Modules that will communicate should use those interfaces during the tests
Today
Quiz
TBA
ASAP: Reinstall IntelliJ if you still use it
Monday: Class time -> Office Hours
Full agenda:
Return Exam
Questions about lab due tomorrow in class?
Threads: Locking on null object
Threads: invokeLater
Threads: The squares example
Decorator Class Diagram
More on Java IO
Class diagrams
Design Principles
in the patterns we’ve seen so far
Compare with alternatives
Decorator vs. array approach suggested in class
Non-decorator array – decorator can be added on without modifying the original hierarchy
Decorator has “before-after” and possibly other combinatorial control that would be hard-coded in array
[Show “screenshot” of discussion from class? Or just re-type?]
Strategy vs. Decorator class diagrams side-by-side
Structural difference (inheritance optional in Strategy pattern?)
Decorator vs. “Strategy” array
Perhaps next:
Coding Starbuzz coffee (?)
Add real patterns
ArrayList – null-checking
Java I/O: Students do coding examples
SE-2811
Slide design: Dr. Mark L. Hornick
Content: Dr. Hornick
Errors: Dr. Yoder
Dr. Josiah Yoder

2. Quiz topics Rate Monotonic Analysis CPU usage
SE3910
5/7/2019
Quiz topics
Rate Monotonic Analysis
CPU usage
Happens-before, caching, reordering, and sequential consistency
Short-answer questions
Code analysis
SE-2811
Dr.Yoder
Dr. Josiah Yoder

3. Textbook references This material comes from TBA
SE3910
5/7/2019
Textbook references
This material comes from
TBA
Chapter 4 of our custom text
Chapter 3 of Laplante & Ovaska, Real-Time Systems Design and Analysis, 4th ed.
Section 3.3: Mailboxes, Semaphores, Deadlocking..
SE-2811
Dr.Yoder
Dr. Josiah Yoder

4. Predicting CPU usage τi – task i pi – period i (ms)
SE3910
5/7/2019
Predicting CPU usage
τi – task i
pi – period i (ms)
ei – execution time (ms)
ui -- %CPU used for task i
SE-2811
Dr.Yoder
Dr. Josiah Yoder

5. Predicting CPU usage (2)
SE3910
5/7/2019
Predicting CPU usage (2)
ui = ei/pi U = 𝑖 𝑢 𝑖
SE-2811
Dr. Yoder
Dr. Josiah Yoder

6. CS2852
5/7/2019
In-Class Exercise
Calculation: What is the processor utilization for this problem?
Based on RMA, what order will they execute and how will they execute?
Hints: Draw release times, break up processing into multiple frames if needed.
Skip calculation if time short
SE Dr. Josiah Yoder
Slide style: Dr. Hornick
Much Material: Dr. Schilling
Dr. Yoder

7. Rate-Monotonic Example
CS2852
5/7/2019
Rate-Monotonic Example
See example soln. in text.
SE Dr. Josiah Yoder
Slide style: Dr. Hornick
Much Material: Dr. Schilling
Dr. Yoder

8. Simplifying Assumptions needed for RMS
SE3910
5/7/2019
Simplifying Assumptions needed for RMS
All tasks in the task set considered are strictly periodic.
The relative deadline of a task is equal to its period.
All tasks are independent; there are no precedence constraints.
No task has any nonpreemptible section, and the cost of preemption is negligible.
Only processing requirements are significant; memory and I/O requirements are negligible.
SE Dr. Josiah Yoder
Slide style: Dr. Hornick
Much Material: Dr. Schilling
Dr. Josiah Yoder

9. When is Rate Monotonic Guaranteed to work?
SE3910
5/7/2019
When is Rate Monotonic Guaranteed to work?
For n tasks, RMA is guaranteed to meet all deadlines if
𝑈≤𝑛( 2 1 𝑛 −1)
For a very large number of tasks (n approaching infinity), RMA is guaranteed to meet all deadlines if
𝑈≤ ln 2 ≈0.69
For many practical applications, RMA will work if
𝑈≤0.85
Dr. Josiah Yoder

10. Multithreading terminology
SE3910
5/7/2019
Multithreading terminology
Semaphores
Signals
Monitors
Mailboxes
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Dr.Yoder
Dr. Josiah Yoder

11. Semaphores Provides: Acquire – obtain a lock on a resource
5/7/2019
Semaphores
Provides:
Acquire – obtain a lock on a resource
Release – release a lock on a resource
Can allow multiple locks up to some fixed amount – e.g. to count how many processes have requested to use a socket
SE-2811
Dr.Yoder
Dr. Josiah Yoder

12. Monitors A monitor is a section of code protected by a lock.
5/7/2019
Monitors
A monitor is a section of code protected by a lock.
e.g. the synchronize statement in Java
e.g. can implement with semaphore
e.g. lock/unlock semantics in C/C++ pthreads, etc.
SE-2811
Dr.Yoder
Dr. Josiah Yoder

13. Signals Essentially a message between different parts of a program
5/7/2019
Signals
Essentially a message between different parts of a program
Implemented in Java: notify/wait
Can implement with semaphores:
Start with semaphore locked
To wait, try to lock on the semaphore
To release, unlock the semaphore
SE-2811
Dr.Yoder
Dr. Josiah Yoder

14. Mailboxes A mailbox provides: send: Send a message to another thread
5/7/2019
Mailboxes
A mailbox provides:
send: Send a message to another thread
receive: Get the message. Block until a message is ready
Rather like TCP.
SE-2811
Dr.Yoder
Dr. Josiah Yoder

15. Consider this code: synchronized(this) { im = getImage(); q.put(im); }
synchronized(this) { im = q.get(im); display(im); }
SE-2811
Dr.Yoder