emit qt signal is very slow how it can be optimized?

[spirit]

it's bad idea to use Qt:: DirectConnection between threads, Qt::QueuedConnection must be used.

[sawerset]

I tried Qt::QueuedConnection and nothing changed.

[spirit]

yes, because by default last parameter in 'connect' is Qt::AutoConnection, which means

If the signal is emitted from the thread in which the receiving object lives, the slot is invoked directly, as with Qt:: DirectConnection; otherwise the signal is queued, as with Qt::QueuedConnection.

try to use customs events, but I think result will not change.
ps. if you use thread just for loading information and don't transform it then you can you only main thread and use qApp->processEvents() in long time operations.

[caduel]

a) Qt::QueuedConnection is the default for threads. So explicitly specifying it won't change anything.

b) simple solutions might be

1. emit the signal not every time but only every 100th time (or so)
2. just open the file in a normal function call, update the gui and call QCoreApplication::processEvents() now and then
3. do not use a thread
4. use a plain callback (do not forget to synchronize access! and don't forget you must not call gui code from another thread!)

HTH