How communicate two threads from QSharedMemory

sayeh_sh

please help me:
i want to communicate 2 threads :
thread1 --> write in a segment of QSharedMemory
thread2 --> read from this segment
I have do this work but i dosen't have open the segment from another class!!!!!!

class 1:
@#include "mythread.h"

#include <QtCore>
#include <QDebug>

MyThread::MyThread()
{

}

void MyThread::run()
{
qDebug() << this->name <<"Running ...";
sleep(3);
QSharedMemory shared("memory");
//shared.setKey("memory");
shared.attach(QSharedMemory::ReadWrite);
shared.lock();
char to = (char)shared.data();
qDebug() << "the content of segment is : " << to;
shared.unlock();

shared.detach();
qDebug() << "segment is deleted";

}
@

class 2:
@#include "thread.h"

#include <QtCore>
#include <QDebug>

Thread::Thread()
{
}

void Thread::run()
{
qDebug() << this->name <<"Runned thread2 MSG!!!";

QSharedMemory shared("memory");
if(!shared.create(1024,QSharedMemory::ReadWrite))
{
    qDebug() << "segment not be create!!!";
}
qDebug() << "segment memoire crée";
shared.lock();
char *to = (char*)shared.data();
char *text = "SND_SV1_LCH_DATA";
memcpy(to, text, strlen(text)+1);
shared.unlock();
qDebug()<<"thread2 terminated";

}@

main :
@
#include <QCoreApplication>
#include "mythread.h"
#include "thread.h"

int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);

MyThread mThread1;
mThread1.name = "mThread1";


Thread mThread2;
mThread2.name = "mThread2";

QMutex mutex;
mutex.lock();
mThread2.start();
mutex.unlock();

sleep(5);

mutex.lock();
mThread1.start();
mutex.unlock();


//mThread1.Stop = false;


return a.exec(&#41;;

}@

SGaist

Hi and welcome to devnet,

You are creating the threads in the wrong order. You start by creating the thread that attaches to the QSharedMemory and then the thread that creates it. It's the other way around.

sayeh_sh

thnx for your response
i inversed the order of threads but it's still wrong.
please you can help me!!

SGaist

I didn't pay attention to one detail.

Short version: in your run code, you are creating the QSharedMemory, writing to it and then, end of the function. This means that your QSharedMemory goes out of scope thus it's destroyed even before you start your second thread.

sayeh_sh

so i do it in this case!!
and it can possible to give me some example illustrate a communication between 3 process 1 parent and 2 childs using QProcess and QSharedMemory!!!!

SGaist

Less exclamation points please.

So this is school work...

Search Qt's documentation for the shared memory documentation and example.

Study the example carefully, it contains everything you need to get going.