Today Return Quiz First release of final project template Multithreading Options

Qt socket buffers between threads Tomorrow: Quiz

Interthread communication in Qt

SE-2811Slide design: Dr. Mark L. Hornick

Content: Dr. HornickErrors: Dr. Yoder

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SE3910Week 8, Class 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

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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/java-threads-vs-pthreads

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Task States (more essential rambling)

Wiki:Process (computing)See also Laplante and Ovaske 4E p. 97SE-2811

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Threading – pthreads (review) Java Pthreadsjava.lang.Thread #include <pthread.h>No external jar needed link with -pthreadThread t = new Thread(r)t.start();

pthread_create(t,r,sr,a)

interface Runnable {void run(); }

Parameter:void* (*sr) (void *)

t.join(); pthread_join(*t, &p)Object o; pthread_mutex_init(m,null)synchronized(o) {…} … /* Garbage coll. */

pthread_mutex_lock(…)…pthread_mutex_destroy(…)

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Threading – pthreads (updated with links)Java PthreadsObject 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);

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• 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

Ex: Edit to include notify/wait to interleave these threads.Consider this code-snippetQueue q = ……synchronized(q) { while(true) { img = getImage(); q.offer(img); }}

// on another thread

synchronized(q) { while(true) { img = q.poll(); showImage(); }}

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Threading – qthreads (with corrections) Java qthreads

java.lang.Thread #include <QThread>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; QMutexsynchronized(o) {…} … /* Garbage coll. */

Avoid sharing memory entirely…… see code example…???? 8

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.

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Qt’s connect method http://doc.qt.io/qt-5/qobject.html#connect http://

doc.qt.io/qt-5/qt.html#ConnectionType-enum

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Qt Connection types

Constant Value Description

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.

Qt::DirectConnection 1 The slot is invoked immediately when the signal is emitted. The

slot is executed in the signalling thread.

Qt::QueuedConnection 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::BlockingQueuedConnection 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::UniqueConnection 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.

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http://doc.qt.io/qt-5/qt.html#ConnectionType-enum

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 Click start // what happens? (For Java? For Qt?) Click stop // what happens? (For Java? For Qt?)

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A bit more on the Rate Monotonic Analysis

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Possibly Fun Very simple C++ wrapper for pthreads

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.pdfSE-3910 - Dr. Josiah Yoder

Slide style: Dr. HornickMuch Material: Dr. Schilling

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Certainly fun (Dr. Taylor’s Reviews) 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

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Other references 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

https://pic.dhe.ibm.com/infocenter/iseries/v7r1m0/index.jsp?topic=%2Fapis%2Fusers_75.htm IBM example of using pthread_cond_init

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Standards http://pubs.opengroup.org/onlinepubs/790879

9/xsh/pthread.h.html pthead.h

http://pubs.opengroup.org/onlinepubs/7908799/xsh/systypes.h.html systypes.h – for xxxx_t

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Muddiest Point

Wait for the slides, or follow this link to answer both questions at once: http://bit.ly/1Mow5a3

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

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

References

EBB: Derek Malloy, Exploring Beaglebone, Wiley, 2015RTS: Laplante and Ovaska, Real-Time Systems Design and Analysis by, Fourth Edition, Wiley, 2012

SE-2811Slide design: Dr. Mark L. Hornick

Content: Dr. HornickErrors: Dr. Yoder

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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

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Task States

Wiki:Process (computing)See also Laplante and Ovaske 4E p. 97SE-2811

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