Qt Socket blocking functions required to run in QThread where created. Any way past this?
- by Alexander Kondratskiy
The title is very cryptic, so here goes!
I am writing a client that behaves in a very synchronous manner. Due to the design of the protocol and the server, everything has to happen sequentially (send request, wait for reply, service reply etc.), so I am using blocking sockets. Here is where Qt comes in.
In my application I have a GUI thread, a command processing thread and a scripting engine thread. I create the QTcpSocket in the command processing thread, as part of my Client class. The Client class has various methods that boil down to writing to the socket, reading back a specific number of bytes, and returning a result.
The problem comes when I try to directly call Client methods from the scripting engine thread. The Qt sockets randomly time out and when using a debug build of Qt, I get these warnings:
QSocketNotifier: socket notifiers cannot be enabled from another thread
QSocketNotifier: socket notifiers cannot be disabled from another thread
Anytime I call these methods from the command processing thread (where Client was created), I do not get these problems.
To simply phrase the situation:
Calling blocking functions of QAbstractSocket, like waitForReadyRead(), from a thread other than the one where the socket was created (dynamically allocated), causes random behaviour and debug asserts/warnings.
Anyone else experienced this? Ways around it?
Thanks in advance.
