Timer (Apache Beam 2.23.0)

```
@Experimental(value=TIMERS)
public interface Timer
```
A timer for a specified time domain that can be set to register the desire for further processing at particular time in its specified time domain.
See TimeDomain for details on the time domains available.
In a DoFn, a Timer is specified by a TimerSpec annotated with DoFn.TimerId.
An implementation of Timer is implicitly scoped - it may be scoped to a key and window, or a key, window, and trigger, etc.
A timer exists in one of two states: set or unset. A timer can be set only for a single time per scope.
Timer callbacks are not guaranteed to be called immediately according to the local view of the TimeDomain, but will be called at some time after the requested time, in timestamp order.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method and Description
`Timer`	`align(Duration period)` Aligns the target timestamp used by `setRelative()` to the next boundary of `period`.
`Timer`	`offset(Duration offset)` Offsets the target timestamp used by `setRelative()` by the given duration.
`void`	`set(Instant absoluteTime)` Sets or resets the time in the timer's `TimeDomain` at which it should fire.
`void`	`setRelative()` Sets the timer relative to the current time, according to any offset and alignment specified.
`Timer`	`withOutputTimestamp(Instant outputTime)` Sets event time timer's output timestamp.

- Method Detail
  - set
```
void set(Instant absoluteTime)
```
    Sets or resets the time in the timer's TimeDomain at which it should fire. If the timer was already set, resets it to the new requested time.
    For TimeDomain.PROCESSING_TIME, the behavior is be unpredictable, since processing time timers are ignored after a window has expired. Instead, it is recommended to use setRelative().
    If the output timestamp has not been explicitly set then the default output timestamp per TimeDomain is:
    - TimeDomain.EVENT_TIME: the firing time of this new timer.
    - TimeDomain.PROCESSING_TIME: current element's timestamp or current timer's output timestamp.
    - TimeDomain.SYNCHRONIZED_PROCESSING_TIME: current element's timestamp or current timer's output timestamp.
  - setRelative
```
void setRelative()
```
    Sets the timer relative to the current time, according to any offset and alignment specified. Using offset(Duration) and align(Duration).
    If the output timestamp has not been explicitly set then the default output timestamp per TimeDomain is:
    - TimeDomain.EVENT_TIME: the firing time of this new timer.
    - TimeDomain.PROCESSING_TIME: current element's timestamp or current timer's output timestamp.
    - TimeDomain.SYNCHRONIZED_PROCESSING_TIME: current element's timestamp or current timer's output timestamp.
  - offset
```
Timer offset(Duration offset)
```
    Offsets the target timestamp used by setRelative() by the given duration.
  - align
```
Timer align(Duration period)
```
    Aligns the target timestamp used by setRelative() to the next boundary of period.
  - withOutputTimestamp
```
Timer withOutputTimestamp(Instant outputTime)
```
    Sets event time timer's output timestamp. Output watermark will be held at this timestamp until the timer fires.

Interface Timer

Method Summary

Method Detail

set

setRelative

offset

align

withOutputTimestamp