Quote Originally Posted by prof.ebral View Post
As far as I understand data sent by signals is sent to the main thread.
There are two things here. "Data" (as in arguments to signals) are not sent to any thread, in the meaning that thread affinity of them does not change in any way. If you pass a pointer to a QObject that lives in thread A to thread B, then accessing that object there might cause data corruption or worse. If you pass some non-QObject by pointer then it doesn't have any thread affinity and it is its thread-safety that decides whether this is safe or not. if you pass a non-QObject by value then it is copied and in regular cases will have no notion of its other clone being accessed from the original thread. However another topic is if we interpret what you said as "signals are sent to the main thread" in which case this is not true -- signals are sent in the thread they are emitted in (it's just a plain function call) but connecting to them may cause an event to be posted to an object living in a different thread (it doesn't have to be the "main" thread though).