1. Today Return Quiz First release of final project template Multithreading Options Qt socket buffers between threads Tomorrow: Quiz Interthread communication in Qt SE-2811 Slide design: Dr. Mark L. Hornick Content: Dr. Hornick Errors: Dr. Yoder 1 SE3910 Week 8, Class 2

2. Options for multithreading (review) pthreads POSIX (Linux/Unix standard) threads Can use in C/C++ qthreads Qt Threads Object-Oriented Uses pthreads under the hood, when on POSIX [1] Derek Malloy’s GPIO class Uses pthreads under the hood, but is single- threaded Boost (Please discuss this with me BEFORE HAND if you want to use it.) [1] http://stackoverflow.com/questions/4140189/qthreads-vs- pthreads 2

3. I was asked this question in an interview today…. (continued) "When we create a thread with pthread_create() (POSIX Threads), the thread starts on its own. Why do we need to explicitly call start() in Java. What is the reason that Java doesnt start the thread when we create an instance of it." I was blank and interviewer was short of time and eventually he couldnt explain the reason to me. http://stackoverflow.com/questions/5269535/jav a-threads-vs-pthreads SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 3

4. Task States (more essential rambling) Wiki:Process (computing) See also Laplante and Ovaske 4E p. 97 SE-2811 Dr.Yoder 4

5. Threading – pthreads (review) JavaPthreads java.lang.Thread#include No external jar neededlink with -pthread Thread t = new Thread(r) t.start(); pthread_create(t,r,sr,a) interface Runnable { void run(); } Parameter: void* (*sr) (void *) t.join()t.join();pthread_join(*t, &p) Object o;pthread_mutex_init(m,null) synchronized(o) { … } … /* Garbage coll. */ pthread_mutex_lock(…) … pthread_mutex_destroy(…) 5

6. Threading – pthreads (updated with links) JavaPthreads Object o; o.notify(); phread_cond_t c = PTHREAD_COND_INITIALIZER; pthread_cond_broadcast(c); o.wait();pthread_cond_wait(c,m); o.notify();phtread_cond_signal(c); o.notifyAll();phtread_cond_broadcast(c); SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 6 See Java coding example NotifyWaitExample Caveat: “POSIX threads can wait at condition variables of a greater generality than available in Java, but the corresponding queues may be leaky.” http://wimhesselink.nl/pub/whh241b.pdf

7. Ex: Edit to include notify/wait to interleave these threads. Consider this code- snippet Queue q = … … synchronized(q) { while(true) { img = getImage(); q.offer(img); } // on another thread synchronized(q) { while(true) { img = q.poll(); showImage(); } SE-2811 Dr.Yoder 7

8. Threading – qthreads (with corrections) Javaqthreads java.lang.Thread#include No external jar needed(moc and friends take care of this) Thread t = new Thread(r) t.start(); QThread *t = new QThread; moveToThread(t); // note here interface Runnable { void run(); } QObject (e.g. QWidget (e.g. QMainWindow)) t.join(); connect the QThread::finish() signal to a slot that checks if all threads are done. Object o;QMutex synchronized(o) { … } … /* Garbage coll. */ Avoid sharing memory entirely… … see code example… ???? 8

9. Useful if you are into Qt slots/signals == events “A QThread should be used much like a regular thread instance: prepare an object (QObject) class with all your desired functionality in it. Then create a new QThread instance, push the QObject onto it using moveToThread(QThread*) of the QObject instance and call start() on the QThread instance. That’s all. ” https://mayaposch.wordpress.com/2011/11/01/how -to-really-truly-use-qthreads-the-full-explanation/ I have successfully used this approach. SE-2811 Dr.Yoder 9

10. Qt’s connect method http://doc.qt.io/qt-5/qobject.html#connect http://doc.qt.io/qt-5/qt.html#ConnectionType- enum http://doc.qt.io/qt-5/qt.html#ConnectionType- enum SE-2811 Dr.Yoder 10

11. Qt Connection types ConstantValueDescription Qt::AutoConnection 0 (Default) If the receiver lives inthe thread that emits the signal, Qt::DirectConnection is used. Otherwise, Qt::QueuedConnection is used. The connection type is determined when the signal is emitted.lives in Qt::Direct Connection 1 The slot is invoked immediately when the signal is emitted. The slot is executed in the signalling thread. Qt::Queued Connection 2 The slot is invoked when control returns to the event loop of the receiver's thread. The slot is executed inhe t receiver's thread. Qt::Blocking QueuedConnection 3 Same as Qt::QueuedConnection, except that the signalling thread blocks until the slot returns. This connection must not be used if the receiver lives in the signalling thread, or else the application will deadlock. Qt::Unique Connection 0x80 This is a flag that can be combined with any one of the above connection types, using a bitwise OR. When Qt::UniqueConnection is set,QObject::connect() will fail if the connection already exists (i.e. if the same signal is already connected to the same slot for the same pair of objects). This flag was introduced in Qt 4.6.QObject::connect SE-2811 Dr.Yoder 11 http://doc.qt.io/qt-5/qt.html#ConnectionType-enum

12. Coding example. Exercise: Both the Java and Qt solutions will behave poorly if I start multiple threads. Predict how each solution will behave if I: Click start // what happens? (For Java? For Qt?) Click stop // what happens? (For Java? For Qt?) SE-2811 Dr.Yoder 12

13. A bit more on the Rate Monotonic Analysis SE-2811 Dr.Yoder 13

14. Possibly Fun Very simple C++ wrapper for pthreads http://www.cs.utexas.edu/users/lavender/courses/ cs345/lectures/CS345-Lecture-09.pdf http://www.cs.utexas.edu/users/lavender/courses/ cs345/lectures/CS345-Lecture-09.pdf notify/wait – example comparison with Java and pthreads http://wimhesselink.nl/pub/whh241b.pdf Compares create for Java, pthreads, and Win32 threads http://cs.millersville.edu/~csweb/lib/userfiles/9Thre adsII.pdf http://cs.millersville.edu/~csweb/lib/userfiles/9Thre adsII.pdf SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 14

15. Certainly fun (Dr. Taylor’s Reviews) http://msoe.us/taylor/tutorial/ce2810/functionp ointers http://msoe.us/taylor/tutorial/ce2810/functionp ointers Function Pointers http://msoe.us/taylor/tutorial/ce2810/csimilar C/C++/Java http://msoe.us/taylor/tutorial/ce2810/ooc Object-Oriented C SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 15

16. Other references http://granite.sru.edu/~whit/cpsc464/Notes/fig s/02-14.jpg http://granite.sru.edu/~whit/cpsc464/Notes/fig s/02-14.jpg Simple pthread chart From http://granite.sru.edu/~whit/cpsc464/Notes/ch2.html http://granite.sru.edu/~whit/cpsc464/Notes/ch2.html https://pic.dhe.ibm.com/infocenter/iseries/v7r 1m0/index.jsp?topic=%2Fapis%2Fusers_75. htm https://pic.dhe.ibm.com/infocenter/iseries/v7r 1m0/index.jsp?topic=%2Fapis%2Fusers_75. htm IBM example of using pthread_cond_init SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 16

17. Standards http://pubs.opengroup.org/onlinepubs/790879 9/xsh/pthread.h.html http://pubs.opengroup.org/onlinepubs/790879 9/xsh/pthread.h.html pthead.h http://pubs.opengroup.org/onlinepubs/790879 9/xsh/systypes.h.html http://pubs.opengroup.org/onlinepubs/790879 9/xsh/systypes.h.html systypes.h – for xxxx_t SE-3910 - Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 17

18. Muddiest Point Wait for the slides, or follow this link to answer both questions at once: http://bit.ly/1Mow5a3 SE-2811 Dr.Yoder 18

19. SE-2811 Dr. Josiah Yoder 19 http://bit.ly/1Mow5a3

20. SE-2811 Dr. Josiah Yoder 20 http://bit.ly/1Mow5a3

21. References EBB: Derek Malloy, Exploring Beaglebone, Wiley, 2015 RTS: Laplante and Ovaska, Real-Time Systems Design and Analysis by, Fourth Edition, Wiley, 2012 SE-2811 Slide design: Dr. Mark L. Hornick Content: Dr. Hornick Errors: Dr. Yoder 21

22. Someday soon Late next week? Real-Time Operating Systems What is a RTOS? How does it relate to the rest? OS roles Interrupts and the OS Definitions, Flowchart, Timing diagram Detailed steps Scheduling Task states & pre-runtime vs runtime SE-2811 Dr.Yoder 22

23. Task States Wiki:Process (computing) See also Laplante and Ovaske 4E p. 97 SE-2811 Dr.Yoder 23