QT3 -- How does a gui communicate with a worker thread?

[wysota]

QT3 -- How does a gui communicate with a worker thread?

Using events.

I have a simple gui that creates and then launches a thread (derived from QThread). The thread does some continuous processing and remains for the life of the gui. In order for the thread to communicate with the gui, I use postevent -- which, as I understand, is the correct way for a thread to communicate with the gui.

That's correct.

However, I am not sure how to safely communicate from the gui to the thread.

Basically, you can't. You can only use mutexes and a shared variable. Hard to call that "communication" though.

[Ronayn]

Wysota, your first answer contradicts your third. To be crystal on this point, a QThread can use events to communicate (one-way) to the gui, but the gui cannot post events to the QThread (because it doesn't have an event loop). That is correct, yes?

So, you are saying QT3 doesnt provide a safe way for the gui to communicate to a QThread? If so, that's a bummer

Does QT4? (if you know)

[wysota]

Wysota, your first answer contradicts your third.

No, it doesn't

To be crystal on this point, a QThread can use events to communicate (one-way) to the gui, but the gui cannot post events to the QThread (because it doesn't have an event loop). That is correct, yes?

Yes, only one-way communication is safe in Qt3.

So, you are saying QT3 doesnt provide a safe way for the gui to communicate to a QThread? If so, that's a bummer

Not anything built-in. You can only use a mutex, have a queue of messages and periodically check the queue from within the thread.

Does QT4? (if you know)

Yes, in Qt4 you can use signals and slots and events (both ways).