buildCompletable

Builds a completable that can be completed, executing all deferred actions in reverse order of their registration.

Add actions to be executed with addCancelable and addCompletable. The actions will be executed eagerly when the completable is created.

Every action can register deferred actions to be executed when the completable is completed. Those will be executed in reverse order of their registration.

When a completable is completed, no more actions will be executed. The completion will finish the currently executing action and all deferred actions in reverse order of their registration.