QThread - readers and writer

qwe3

Hi,

I would like to learn how to use QThread and QSemaphore. I started with mission, where I have 2 readers and 1 writer. There is sharedVariable, which I increment in writer Object. I would like to read this variable's value in reader Objects. I debuq information about threadID and variable value.

I would like to achieve ( for example thread 1 with reader is 0x1 and thread 2 with other reader is x02 ):
0x1 1
0x2 1
0x1 2
0x2 2
0x1 3
0x2 3
0x1 4
0x2 4
0x1 5
0x2 5

Now I get ( my debuq - this is only part ):
0x1e28 38
0x1e28 38
0x1e28 38
0x1e28 38
0x1e28 46
0x1e28 46
0x1e28 46

So for example I don't get on debuq value 39, 40, 41, 42.

And...
I see each value which is presented only in one thread like this:
0x1e28 215
0x1e28 215
0x1e28 215
0x1e28 218
0x1e28 218
0x1e28 218

215 is only in 0x1e28 debuq and 218 is only in 0x1e28 thread.

My codes:
WriterClass

#include "writerclass.h"
#include <QDebug>

WriterClass::WriterClass(int &sharedVariable, QSemaphore *sharedSemaphore): sharedVar(sharedVariable), sharedSem(sharedSemaphore)
{}

void WriterClass::process()
{
    for(int i=0;i<1000;i++)
    {
         sharedSem->acquire(1);
         sharedVar++;
         sharedSem->release(1);
    }
    emit finished();
}

Reader Class:

#include "readerclass.h"
#include <QDebug>

ReaderClass::ReaderClass(int &sharedVariable, QSemaphore *sharedSemaphore): sharedVar(sharedVariable), sharedSem(sharedSemaphore)
{}

void ReaderClass::process()
{
    while(1)
    {
        sharedSem->acquire(1);
        qInfo()<<QThread::currentThreadId()<<sharedVar;
        if(sharedVar == 1000)
        {
            break;
        }
        sharedSem->release(1);
    }
    emit finished();
}

and mainWindow ( number is int and this is class variable, which started with value 0 ):

    sem = new QSemaphore(1);
    ReaderClass *reader = new ReaderClass(number,sem);
    ReaderClass *reader2 = new ReaderClass(number,sem);
    WriterClass *writer1 = new WriterClass(number,sem);

    QThread* thread = new QThread;
    QThread* thread2 = new QThread;
    QThread* thread3 = new QThread;
    reader->moveToThread(thread);
    writer1->moveToThread(thread2);
    reader2->moveToThread(thread3);

    connect(thread, SIGNAL(started()), reader, SLOT(process()));
    connect(reader, SIGNAL(finished()), thread, SLOT(quit()));
    connect(reader, SIGNAL(finished()), reader, SLOT(deleteLater()));
    connect(thread, SIGNAL(finished()), thread, SLOT(deleteLater()));

    connect(thread2, SIGNAL(started()), writer1, SLOT(process()));
    connect(writer1, SIGNAL(finished()), thread2, SLOT(quit()));
    connect(writer1, SIGNAL(finished()), writer1, SLOT(deleteLater()));
    connect(thread2, SIGNAL(finished()), thread2, SLOT(deleteLater()));

    connect(thread3, SIGNAL(started()), reader2, SLOT(process()));
    connect(reader2, SIGNAL(finished()), thread3, SLOT(quit()));
    connect(reader2, SIGNAL(finished()), reader2, SLOT(deleteLater()));
    connect(thread3, SIGNAL(finished()), thread3, SLOT(deleteLater()));

    thread->start();
    thread2->start();
    thread3->start();

Christian Ehrlicher

Why do you think that after the reader executes sharedSem->release(1) a thread context will happen? Same goes for the writer thread.

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QThread - readers and writer