Class Meeting #19: Review for Exam, Threads

Topics for Today

• Assignment #3: if you worked in a team on the original gizmo controller assignment you are required to choose a new partner for this one
• Review for midterm exam (see below)
• Review correct use of mutexes and conditions variables with threads, and design of gizmo controller using threads (see further below)

Topics Covered on Midterm Examination

1. No excuse for missing anything on the prior quizzes!
   • quiz0106.html
   • quiz0206.html
   • quiz0306.html
   • quiz0406.html
2. No excuse either for missing anything on the prior midterms exams:
   • 2003
   • 1998
3. Do not assume the exam this term will be so similar to these two as they were to one another!
4. See next slide for an independent list of topics

More Topics to Study for Midterm Examination

• Critical zone definition, theorem, and proof for preemptive fixed-priority scheduling of independent periodic and sporadic tasks on one CPU
• EDF and Rate monotonic utilization bound theorems
• Response-time test for fixed-priority preemptive scheduling of independent periodic ans sporadic tasks on one CPU
• Definition of priority inversion, why is it a problem, and how to bound it using mutexes with priority inheritance or non-preemption.
• Demand bound and load bound functions, and how to estimate them experimentally via benchmark program (your last assignment)

An OO Thread-based Design for Gizmo Controller

• Sensor thread - periodically polls sensors, and maintains estimated position of blade; adjusts period of solenoid thread if necessary; may also wake up LED thread
• Solenoid thread - periodically pulses solenoid; sleeps briefly between turning solenoid on and turning it off; may wake up LED thread if that is not done by Sensor thread
• LED thread - periodically outputs new LED settings from message buffer; may sleep during periods when LEDs need to stay out
• Input thread (main) - reads test input from user, and updates message buffer; may shut down other threads

Set priorities according to rate monotonic model

Main issue now becomes how to safely share state

Safe Sharing of Data between Threads

1. Single writer solutions, using volatile atomic variables
2. Protection with mutexes

See examples via links below for details on both.

Signaling Events between Threads

1. Use condition variables
2. Always use pthread_cond_wait in a loop with a state variable test
3. Allow for spurious and multiple wake-ups
4. Protect the state variable with a mutex

Notes and Examples of Thread Programming

Including correct usage of condition variables and mutexes

• POSIX Threads API
• Producer-Consumer Synchronization Using POSIX Threads
• Dining Philosphers Synchronization Using POSIX Threads

Things for You to Do

• Read Chapter 7 of the text
• Review chapter 1-6 and class notes, in preparation for midterm exam on 02 November
• Work on redoing gizmo controller using threads