| slot | A slot to call when polling socket results in an event that matches condition. The event will be passed as a parameter to slot. If io_handler() returns false the handler is disconnected. |
| socket | The Socket object to watch. |
| condition | The conditions to watch for. |
| cancellable | A Cancellable object which can be used to cancel the source, which will cause the source to trigger, reporting the current condition (which is likely 0 unless cancellation happened at the same time as a condition change). You can check for this in the callback using Cancellable::is_cancelled(). |
| priority | The priority of the new event source. |