Sharing data across Qt threads

Question

I\'m new to Qt so please excuse the simplicity of the question but I\'m a bit confused on the Qt threading. Let\'s say I have 3 threads: the main default GUI thread, and 2

Answer 1

With Qt, the easiest way to send information between threads is to use signals and slots. Qt automatically uses queued signals for connections between threads (see Qt::ConnectionType), which ensures that a signal can be emitted from one thread, but the slot will be executed in the thread of the receiver object.

If the data being sent between threads (work to be done or status information) is something that Qt can automatically queue (e.g., QStrings, built-in types like int and double, and others), then passing the info as the arguments to the signal/slot is the best way to send the info. If large or complex data is being shared, then you either need to use qRegisterMetaType to allow Qt to copy the data, or pass a pointer to a thread-safe object. Unlike what Pie_Jesu said, the threads do share an address space so you can share pointers; just make sure that one thread's interaction with the shared object won't interfere with another thread's interactions.

QTcpSocket is not thread-safe (it's only reentrant according to Qt's documentation), so if you share the socket you will have to be responsible for ensuring that threads don't use the socket in conflicting ways.