The term slot is used to describe a narrow opening or groove in something. It can also refer to a time slot in a machine.
When a signal is emitted by a class that is connected to a slot, the corresponding slot will call a function. This function will have to run at least ten times slower than if the signal was called directly.
Slots are also used to receive signals. If a slot is expecting a signal, the slot will report a runtime error. However, the slot won’t know whether the signal is connected to it.
Slots are similar to callbacks, except that they are slightly slower. Emitting a signal with a slot will only incur overhead if it is indirectly calling more than ten functions.
Unlike callbacks, slots are not aware of how many other components are connected to them. They can be invoked by any component.
Slots follow the normal C++ rules when called directly. If a signal is emitted from an arbitrary class, the private slot will be invoked in an unrelated class.
The Slot estimator in BigQuery can help you manage slot capacity based on historical performance metrics. It displays job performance data from the past seven days, including how your job performs at different capacity levels. You can use it to calculate how adding or reducing slot capacity will impact your jobs. Moreover, you can model the cost of slot capacity and make recommendations for on-demand billing.