Set the event callback function and user data that will be called when collectpads has received an event originating from one of the collected pads.
If the event being processed is a serialized one, this callback is called with this STREAM_LOCK held, otherwise not. As this lock should be held when calling a number of CollectPads functions, it should be acquired if so (unusually) needed.
MT safe.
| this |
the collectpads to use |
| func |
the function to set |
| user_data |
user data passed to the function |