1. Slide design: Dr. Mark L. Hornick
SE3910
4/24/2019
SE3910 Week 9, Class 3
Today
Multithreading in Java and C++11
Monday: Class time -> Office Hours / Demo time (Perhaps in S-365)
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. SE3910
4/24/2019
Lab Announcements
To link to OpenCV from Qt, please add these lines at the end of your .pro file:
unix: CONFIG += link_pkgconfig unix: PKGCONFIG += opencv
If you are getting many underflows, you may want to check that the CPU is set to its maximum frequency. On the BB, run the commands 
cpufreq-info
cpufreq-set -f 1000MHz 
to get the frequency set correctly. (Thanks, Dr. Schilling.)
SE-2811
Dr.Yoder
Dr. Josiah Yoder

3. SE3910
4/24/2019
Lab Announcements
When checking out a kit for an LCD, check out two kits. If you have any trouble getting it to boot to a Desktop, shutdown and use the other LCD. Or come to my office and borrow mine.
When debugging on the desktop, you may want to use a script to automatically capture the output of your commands. e.g., containing:
./mylab8 arguments > output.txt 2> errror.txt
Dr. Josiah Yoder

4. Total and Partial Order
SE2811
4/24/2019
Total and Partial Order
Each thread has a Total Order
Without synchronize or volatile, actions are concurrent ?
In a partial order, some “happens-before” relationships are specified, but not all.
In a total order, all “happens-before” relationships are specified. (So there is only one way through the program)
For any given multithreaded program, different total orders are possible.
But from a synchronization perspective, each thread has only one intra-thread total order. This is the “Program order” of that thread.
SE-2811
Dr.Yoder
Dr. Josiah Yoder

5. Total and Partial Order
SE2811
4/24/2019
Total and Partial Order
Partial Order
One Total Order
In a partial order, some “happens-before” relationships are specified, but not all.
In a total order, all “happens-before” relationships are specified. (So there is only one way through the program)
SE-2811
Dr.Yoder
Dr. Josiah Yoder

6. Total and Partial Order
SE2811
4/24/2019
Total and Partial Order
Partial Order
One Total Order
In a partial order, some “happens-before” relationships are specified, but not all.
In a total order, all “happens-before” relationships are specified. (So there is only one way through the program)
SE-2811
Dr.Yoder
Dr. Josiah Yoder

7. Total and Partial Order
SE2811
4/24/2019
Total and Partial Order
Partial Order
Another Total Order
In a partial order, some “happens-before” relationships are specified, but not all.
In a total order, all “happens-before” relationships are specified. (So there is only one way through the program)
For any given multithreaded program, different total orders are possible when the program runs. These are called the “Execution order”
But from a synchronization perspective, each thread has only one intra-thread total order.
SE-2811
Dr.Yoder
Dr. Josiah Yoder

8. Total and Partial Order
SE2811
4/24/2019
Total and Partial Order
Partial Order
Another Total Order
In a partial order, some “happens-before” relationships are specified, but not all.
In a total order, all “happens-before” relationships are specified. (So there is only one way through the program)
For any given multithreaded program, different total orders are possible when the program runs. These are called the “Execution order”
But from a synchronization perspective, each thread has only one intra-thread total order.
SE-2811
Dr.Yoder
Dr. Josiah Yoder

9. Languages using Happens-Before
SE3910
4/24/2019
Languages using Happens-Before
Java
C++11
Golang
LLVM (Technically not a language, but a compiler infrastructure, but it does include an intermediate representation language)
SE-2811
Dr.Yoder
Dr. Josiah Yoder

10. Happens-Before in C++11 Some are transitive
SE3910
4/24/2019
Happens-Before in C++11
Some are transitive
“If we ignore consume operations and the dependency-ordered-before relation in C++11, the remaining forms of happens-before end up being transitive.” (Preshing)
Specifications are notoriously difficult to understand, even the most precise ones.
This question clarifies exactly where the C++11 defines what happens-before means.
The asker is confused because they say A is true if B is true instead of A is true if and only if B is true.
Important to our current discussion: I don’t have access to the C++11 specification. It is not an open standard. You have to purchase a copy, which I have not done. (or at least it doesn’t pop up on Google)
SE-2811
Dr.Yoder
Dr. Josiah Yoder

11. Example http://en.cppreference.com/w/cpp/atomic/memory_order
SE3910
4/24/2019
Example
#include <thread> #include <atomic> #include <cassert> #include <string> std::atomic<std::string*> ptr; int data; void producer() { std::string* p = new std::string("Hello"); data = 42; ptr.store(p, std::memory_order_release); }
void consumer() { std::string* p2; while (!(p2 = ptr.load(std::memory_order_acquire))) /* do nothing */; assert(*p2 == "Hello"); // never fires assert(data == 42); // never fires } int main() std::thread t1(producer); std::thread t2(consumer); t1.join(); t2.join();
SE-2811
Dr.Yoder
Dr. Josiah Yoder

12. Consider this code: synchronized(this) { im = getImage(); q.put(im); }
SE3910
4/24/2019
Consider this code:
synchronized(this) { im = getImage(); q.put(im); }
synchronized(this) { im = q.get(im); display(im); }
SE-2811
Dr.Yoder
Dr. Josiah Yoder