Qt: Is the QBuffer thread safe in this code? - c++

Question

The code is given as:
class USBCamCaptureThread : public QThread
{
Q_OBJECT
void run() {
while (!threadQuit){
if (imageReaded){
buffer->reset();
Request = http->get (url->path(),buffer););
}
MG::SLEEP::msleep(250);
}
}
public:
USBCamCaptureThread(){
QFile file("setting_files/cameraIP.txt");
QString line = "192.168.1.5:80"; //default value
if(file.open(QIODevice::ReadOnly)) {
QTextStream in(&file);
line = in.readLine();
}
file.close();
url = new QUrl(line);
http = new QHttp(this);
buffer = new QBuffer(&bytes);
threadQuit = false;
imageReaded = true;
}
~USBCamCaptureThread(){
}
public slots:
void Finished(int requestId, bool error){
QImage localImage;
localImage.loadFromData(bytes);
QImg = localImage;
bytes.clear();
emit signalUSBImageRead();
}
Note that the Finished() is in the main thread, and the run() is in a worker thread.
May question is by reading/writing to the bytes and buffer in separate threads, will it cause thread related issues?

Answer 1

If Finished is called while run is active, then yes, you have a problem. Sharing data between two threads that run in a pipeline (serially) isn't necessarily a problem. Accessing non-threadsafe, shared data between two threads at the same time is always a problem. I haven't used Qt in many years so QBuffer or QImage::loadFromData may offer thread safety guarantees of their own as well.