org.apache.beam.sdk.state

Interface Timer

@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

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().

setRelative

void setRelative()

Sets the timer relative to the current time, according to any offset and alignment specified. Using offset(Duration) and align(Duration).

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.