Share multiple segment with QSharedMemory

boumacmilan

Hi every body

i want to use QSharedMemory to share data between 2 applications using it for sharing one segment works perfectly but when i try 2 share more than one i have access just to the last one

this my code

sharedMemroy.cpp in the first application

@
void SharedMemory::loadIntoSharedMem(QString memoryKey,QString &data)
{
sharedMem.setKey(memoryKey);
if (sharedMem.isAttached())
{
sharedMem.detach();
}
if( data.length())
{
// load into shared memory
QBuffer buffer;
buffer.open(QBuffer::ReadWrite);
QDataStream out(&buffer);
out << data;
int size = buffer.size();

     if (!sharedMem.create(size)) {
         qDebug()<<"Unable to create shared memory segment."<<sharedMem.isAttached()<<" "<<sharedMem.error();

     }

     sharedMem.lock();
     char *to = (char*)sharedMem.data();
     const char *from = buffer.data().data();
     memcpy(to, from, qMin(sharedMem.size(), size));
     sharedMem.unlock();
    }
else
    {
      qDebug()<< "no data to share"
    }

}

@

and in main

@
SharedMemory sh;
sh.loadIntoSharedMem("memo1",data1 );
sh.loadIntoSharedMem("memo2",data2 );
sh.loadIntoSharedMem("memo3",data3 );
@

and on showSharedData.cpp in the seconde application

@
QString ShowSharedMemory::loadFromSharedMem(QString memoryKey)
{
sharedMem.setKey(memoryKey);
if (!sharedMem.attach())
{
qDebug()<<"Unable to load!";
return"";
}

QBuffer buffer;
QDataStream in(&buffer);
QString text;

sharedMem.lock();
buffer.setData((char*)sharedMem.constData(), sharedMem.size());
buffer.open(QBuffer::ReadOnly);
in >> text;
sharedMem.unlock();

sharedMem.detach();
return text;

}
@

and in main

@
data1=showMemory.loadFromSharedMem("memo1");
data2=showMemory.loadFromSharedMem("memo2");
data3=showMemory.loadFromSharedMem("memo3");
@

thanks for your help

dheerendra

in the first source code I see shared memory key as 'mem' etc. In the reader code you specifying the sharedmemory keys as dddd etc. Why are giving different keys for reader and writer ? It need to be same key for both reader and writer.

boumacmilan

@dheerendra thanks aswring
yes sur it was just a mistake of copy/past :p
but on the code there are the same

SGaist

Hi,

If I remember the QSharedMemory mechanism correctly and following your code, you are creating and destroying the two first and only the third lives long enough to actually share some data

dheerendra

If possible can you share you entire code. I can look and share you the right solution.