Clearing the signal queue

[tbscope]

You can disconnect signals and slots just like you connect them using QObject::disconnect();

[SixDegrees]

Once signals have been emitted, I don't know of any way to "recall" them. You could probably simulate such functionality through the use of, say, a global variable or singleton that would be set to a value indicating that no more signals should be processed, which the receiver would check at the beginning of each function call. Depending on the details of your implementation, it might be possible to send such information along with each signal itself instead of using a global.

As already noted, you can disconnect signals and slots, but that won't purge any signals that have already been sent.