Question

I start coding a small qt application to compute checksums. After the unthreaded code run fine I moved to a more responsive way since the mainwindow blocks while computing a hash of a bigger file.

But calling the run() method failes for unknown reason. I even cleared out the run-method completely. No matter what I do: SIGSEV.

Other threaded code from the qt help compile and run without problems – even threaded code in other apps I coded still run, but this not:

the header:

#include <QThread>
class Hasher : public QThread
{
    Q_OBJECT

public:
    Hasher();
    void computeHash();

protected:
    void run();

};

the implementation

#include "hasher.h"

Hasher::Hasher()
{
}

void Hasher::computeHash() {
    start();
}

void Hasher::run() {
    // compute the hash, but for now simply return
}

caller

Hasher h
h.computeHash();

As I said above all works well without threads but crashes when using threads.
I am using QT 4.7.3 on a 64bit ARCH-Linux – and I am really clueless about this.
Maybe someone can help.

Answer 1

If you do like this your thread will be created on stack and it will be destroyed while the thread is still running !

void myfunction ()
{
 Hasher h
 h.computeHash();

}

NeilMonday’s example works because he has a return a.exec(); in his code which keeps Hasher thread alive on the stack. So you have to make your thread live longer.

1. Either make it a member variable of you class or
2. Create it on the heap like Hasher* h = new Hasher (); or
3. Use QtConcurrentRun and QFuture and do not mess with threads.