QtConcurrent question

[bair]

Things turn out to be not so easy. Yes, I've got 4x speedup, but cycle() function generates huge amount of data (hundreds of megabytes) which should be written to a file, but my attempts to write output data from that function have no success. In my MainWindow class I have static QDataStream member out, and I'm using it for output. During execution there is a lot of qDebug messages "QIODevice::write: ReadOnly device", and output file remains absolutely empty, though if I write something to out before QtConcurrent::map() is started, it is written to a file without problems.
As far as I understand, multiple threads generated by QtConcurrent::map() somehow automatically lock out and prevent each other from writing to it. Or may be I am wrong? Anyway, what could be done to avoid this?

Please give me a hint, I'm stuck and this thing is starting to drive me crazy...

[bair]

Any suggestion would be appreciated. Even something like "RTFM".

[wysota]

You can't access a QIODevice from multiple threads at once, that's for sure. Try returning the data from calculations to the main thread and then writing it sequentially from there.

[bair]

Thank you very much. I was thinking about returning data from the calculations to the main thread, but the problem is that there's too much data to handle, so I was afraid that memory consumption will be unacceptably high. Now I think I'll manage it.

Thanks again, you saved me from many hours of attempts to walk through a brick wall.