Undoes the effect of a previous block call.
A blocked handler is skipped during signal emissions and will not be invoked, unblocking it (for exactly the amount of times it has been blocked before) reverts its "blocked" state, so the handler will be recognized by the signal system and is called upon future or currently ongoing signal emissions (since the order in which handlers are called during signal emissions is deterministic, whether the unblocked handler in question is called as part of a currently ongoing emission depends on how far that emission has proceeded yet).
The handler_id has to be a valid id of a signal handler that is connected to a signal of instance and is
currently blocked.
| instance |
The instance to unblock the signal handler of. |
| handler_id |
Handler id of the handler to be unblocked. |