Today Quiz Multithreading Options Qt socket buffers between threads Quiz today & Tuesday in lab SE-2811 Slide design: Dr. Mark L. Hornick Content: Dr. Hornick Errors: Dr. Yoder 1 SE3910 Week 7, Class 3

Quizzes Today Various unit analyses (e.g. audio rates, video rates, Nyquist theorem) Scheduling Round-robin vs. Cyclic Code Scheduling Rate Monotonic Analysis Compile vs. Link errors In-lab (8-Lab) Interthread communication Ask me on Monday! SE-2811 Dr.Yoder 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] pthreads 3

From my thesis SE-2811 Dr.Yoder 4

From my thesis SE-2811 Dr.Yoder 5

From my thesis (zoom in) SE-2811 Dr.Yoder 6

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. a-threads-vs-pthreads SE Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 7

Threading – qthreads Javaqthreads java.lang.Thread #include No external jar needed(moc and friends take care of this) Thread t = new Thread(r) t.start(); QThread *q = new QThread; moveToThread(o); 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… ???? 8

Threading – qthreads Javaqthreads java.lang.Thread #include No external jar needed(moc and friends take care of this) Thread t = new Thread(r) t.start(); QThread *q = new QThread; moveToThread(o); 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… ???? 9

Looks 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. ” -to-really-truly-use-qthreads-the-full-explanation/ I have now successfully used this approach. SE-2811 Dr.Yoder 10

Possibly Fun Very simple C++ wrapper for pthreads cs345/lectures/CS345-Lecture-09.pdf cs345/lectures/CS345-Lecture-09.pdf notify/wait – example comparison with Java and pthreads Compares create for Java, pthreads, and Win32 threads adsII.pdf adsII.pdf SE Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 11

Certainly fun (Dr. Taylor’s Reviews) ointers ointers Function Pointers C/C++/Java Object-Oriented C SE Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 12

Other references s/02-14.jpg s/02-14.jpg Simple pthread chart From m0/index.jsp?topic=%2Fapis%2Fusers_75. htm 1m0/index.jsp?topic=%2Fapis%2Fusers_75. htm IBM example of using pthread_cond_init SE Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 13

Standards 9/xsh/pthread.h.html 9/xsh/pthread.h.html pthead.h 9/xsh/systypes.h.html 9/xsh/systypes.h.html systypes.h – for xxxx_t SE Dr. Josiah Yoder Slide style: Dr. Hornick Much Material: Dr. Schilling 14

Muddiest Point Wait for the slides, or follow this link to answer both questions at once: SE-2811 Dr.Yoder 15

SE-2811 Dr. Josiah Yoder 16

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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 18

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 19

Task States Wiki:Process (computing) See also Laplante and Ovaske 4E p. 97 SE-2811 Dr.Yoder 20