This commit adds support for `@Scheduled` annotation on reactive
methods and Kotlin suspending functions.
Reactive methods are methods that return a `Publisher` or a subclass
of `Publisher`. The `ReactiveAdapterRegistry` is used to support many
implementations, such as `Flux`, `Mono`, `Flow`, `Single`, etc.
Methods should not take any argument and published values will be
ignored, as they are already with synchronous support.
This is implemented in `ScheduledAnnotationReactiveSupport`, which
"converts" Publishers to `Runnable`. This strategy keeps track of
active Subscriptions in the `ScheduledAnnotationBeanPostProcessor`,
in order to cancel them all in case of shutdown.
The existing scheduling support for tasks is reused, aligning the
triggering behavior with the existing support: cron, fixedDelay and
fixedRate are all supported strategies.
If the `Publisher` errors, the exception is logged at warn level and
otherwise ignored. As a result new `Runnable` instances will be
created for each execution and scheduling will continue.
The only difference with synchronous support is that error signals
will not be thrown by those `Runnable` tasks and will not be made
available to the `org.springframework.util.ErrorHandler` contract.
This is due to the asynchronous and lazy nature of Publishers.
Closes gh-23533
Closes gh-28515
35052f2113