问题
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 threads of my own creation (called WorkerThread). Each of my WorkerThreads inherits from QThread and are permanent threads that every so often wake up and send data out a socket and post status on a GUI element. How is the best way to 1) allow the GUI thread to set data in the WorkerThread object that the WorkerThread thread can use? 2) allow the WorkerThread to send status to the GUI thread to be displayed for the user? 3) Allow both WorkerThreads to use the same socket?
It seems from the documentation that when I create a WorkerThread object it is owned by the creating thread (except for the run method that is a new thread). So how does one set data for the new thread to execute on? Must all the data the new thread uses be global? For instance, I would like the GUI to allow the user to select a packet type for each of the WorkerThreads to send when they wake up. I had assumed that I would put in some slots in the WorkerThread that the GUI thread would signal. When the WorkerThread object received a signal to SetPacketType it would set a member variable that the run method references on each iteration. But after reading the documentation I'm not sure that is the way to do it. If the WorkerThread object is owned by the creating thread (GUI thread in this case) then sending signals to it doesn't cross thread boundaries does it?
Also, what is the proper technique for sharing the socket connection across threads?
Thanks in advance.
回答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.
来源：https://stackoverflow.com/questions/12372301/sharing-data-across-qt-threads