Introduction to Scheduling ZIO Effects

A Schedule[Env, In, Out] is an immutable value that describes a recurring effectful schedule, which runs in some environment Env, after consuming values of type In (errors in the case of retry, or values in the case of repeat) produces values of type Out, and in every step based on input values and the internal state decides to halt or continue after some delay d.

Schedules are defined as a possibly infinite set of intervals spread out over time. Each interval defines a window in which recurrence is possible.

Repetition and retrying are two similar concepts in the domain of scheduling. It is the same concept and idea, only one of them looks for successes and the other one looks for failures.

When schedules are used to repeat or retry effects, the starting boundary of each interval produced by a schedule is used as the moment when the effect will be executed again.

Schedules allow us to define and compose flexible recurrence schedules, which can be used to repeat actions, or retry actions in the event of errors. We will discuss them on the following pages.

A variety of combinators exist for transforming and combining schedules, and the companion object for Schedule contains all common types of schedules, both for performing retrying and repetition.