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/*
* Copyright (C) 2015 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not
* use this file except in compliance with the License. You may obtain a copy of
* the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations under
* the License.
*/
package com.google.cloud.dataflow.sdk.transforms.windowing;
import com.google.cloud.dataflow.sdk.annotations.Experimental;
import com.google.cloud.dataflow.sdk.util.ExecutableTrigger;
import com.google.cloud.dataflow.sdk.util.TimeDomain;
import com.google.cloud.dataflow.sdk.util.state.MergingStateAccessor;
import com.google.cloud.dataflow.sdk.util.state.StateAccessor;
import com.google.common.base.Joiner;
import org.joda.time.Instant;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import javax.annotation.Nullable;
/**
* {@code Trigger}s control when the elements for a specific key and window are output. As elements
* arrive, they are put into one or more windows by a {@link Window} transform and its associated
* {@link WindowFn}, and then passed to the associated {@code Trigger} to determine if the
* {@code Window}s contents should be output.
*
* See {@link com.google.cloud.dataflow.sdk.transforms.GroupByKey} and {@link Window}
* for more information about how grouping with windows works.
*
*
The elements that are assigned to a window since the last time it was fired (or since the
* window was created) are placed into the current window pane. Triggers are evaluated against the
* elements as they are added. When the root trigger fires, the elements in the current pane will be
* output. When the root trigger finishes (indicating it will never fire again), the window is
* closed and any new elements assigned to that window are discarded.
*
*
Several predefined {@code Trigger}s are provided:
*
* - {@link AfterWatermark} for firing when the watermark passes a timestamp determined from
* either the end of the window or the arrival of the first element in a pane.
*
- {@link AfterProcessingTime} for firing after some amount of processing time has elapsed
* (typically since the first element in a pane).
*
- {@link AfterPane} for firing off a property of the elements in the current pane, such as
* the number of elements that have been assigned to the current pane.
*
*
* In addition, {@code Trigger}s can be combined in a variety of ways:
*
* - {@link Repeatedly#forever} to create a trigger that executes forever. Any time its
* argument finishes it gets reset and starts over. Can be combined with
* {@link Trigger#orFinally} to specify a condition that causes the repetition to stop.
*
- {@link AfterEach#inOrder} to execute each trigger in sequence, firing each (and every)
* time that a trigger fires, and advancing to the next trigger in the sequence when it finishes.
*
- {@link AfterFirst#of} to create a trigger that fires after at least one of its arguments
* fires. An {@link AfterFirst} trigger finishes after it fires once.
*
- {@link AfterAll#of} to create a trigger that fires after all least one of its arguments
* have fired at least once. An {@link AfterAll} trigger finishes after it fires once.
*
*
* Each trigger tree is instantiated per-key and per-window. Every trigger in the tree is in one
* of the following states:
*
* - Never Existed - before the trigger has started executing, there is no state associated
* with it anywhere in the system. A trigger moves to the executing state as soon as it
* processes in the current pane.
*
- Executing - while the trigger is receiving items and may fire. While it is in this state,
* it may persist book-keeping information to persisted state, set timers, etc.
*
- Finished - after a trigger finishes, all of its book-keeping data is cleaned up, and the
* system remembers only that it is finished. Entering this state causes us to discard any
* elements in the buffer for that window, as well.
*
*
* Once finished, a trigger cannot return itself back to an earlier state, however a composite
* trigger could reset its sub-triggers.
*
*
Triggers should not build up any state internally since they may be recreated
* between invocations of the callbacks. All important values should be persisted using
* state before the callback returns.
*
* @param {@link BoundedWindow} subclass used to represent the windows used by this
* {@code Trigger}
*/
@Experimental(Experimental.Kind.TRIGGER)
public abstract class Trigger implements Serializable, TriggerBuilder {
/**
* Interface for accessing information about the trigger being executed and other triggers in the
* same tree.
*/
public interface TriggerInfo {
/**
* Returns true if the windowing strategy of the current {@code PCollection} is a merging
* WindowFn. If true, the trigger execution needs to keep enough information to support the
* possibility of {@link Trigger#onMerge} being called. If false, {@link Trigger#onMerge} will
* never be called.
*/
boolean isMerging();
/**
* Access the executable versions of the sub-triggers of the current trigger.
*/
Iterable> subTriggers();
/**
* Access the executable version of the specified sub-trigger.
*/
ExecutableTrigger subTrigger(int subtriggerIndex);
/**
* Returns true if the current trigger is marked finished.
*/
boolean isFinished();
/**
* Return true if the given subtrigger is marked finished.
*/
boolean isFinished(int subtriggerIndex);
/**
* Returns true if all the sub-triggers of the current trigger are marked finished.
*/
boolean areAllSubtriggersFinished();
/**
* Returns an iterable over the unfinished sub-triggers of the current trigger.
*/
Iterable> unfinishedSubTriggers();
/**
* Returns the first unfinished sub-trigger.
*/
ExecutableTrigger firstUnfinishedSubTrigger();
/**
* Clears all keyed state for triggers in the current sub-tree and unsets all the associated
* finished bits.
*/
void resetTree() throws Exception;
/**
* Sets the finished bit for the current trigger.
*/
void setFinished(boolean finished);
/**
* Sets the finished bit for the given sub-trigger.
*/
void setFinished(boolean finished, int subTriggerIndex);
}
/**
* Interact with properties of the trigger being executed, with extensions to deal with the
* merging windows.
*/
public interface MergingTriggerInfo extends TriggerInfo {
/** Return true if the trigger is finished in any window being merged. */
boolean finishedInAnyMergingWindow();
/** Return true if the trigger is finished in all windows being merged. */
boolean finishedInAllMergingWindows();
/** Return the merging windows in which the trigger is finished. */
Iterable getFinishedMergingWindows();
}
/**
* Information accessible to all operational hooks in this {@code Trigger}.
*
* Used directly in {@link Trigger#shouldFire} and {@link Trigger#clear}, and
* extended with additional information in other methods.
*/
public abstract class TriggerContext {
/** Returns the interface for accessing trigger info. */
public abstract TriggerInfo trigger();
/** Returns the interface for accessing persistent state. */
public abstract StateAccessor state();
/** The window that the current context is executing in. */
public abstract W window();
/** Create a sub-context for the given sub-trigger. */
public abstract TriggerContext forTrigger(ExecutableTrigger trigger);
/**
* Removes the timer set in this trigger context for the given {@link Instant}
* and {@link TimeDomain}.
*/
public abstract void deleteTimer(Instant timestamp, TimeDomain domain);
/** The current processing time. */
public abstract Instant currentProcessingTime();
/** The current synchronized upstream processing time or {@code null} if unknown. */
@Nullable
public abstract Instant currentSynchronizedProcessingTime();
/** The current event time for the input or {@code null} if unknown. */
@Nullable
public abstract Instant currentEventTime();
}
/**
* Extended {@link TriggerContext} containing information accessible to the {@link #onElement}
* operational hook.
*/
public abstract class OnElementContext extends TriggerContext {
/** The event timestamp of the element currently being processed. */
public abstract Instant eventTimestamp();
/**
* Sets a timer to fire when the watermark or processing time is beyond the given timestamp.
* Timers are not guaranteed to fire immediately, but will be delivered at some time afterwards.
*
* As with {@link #state}, timers are implicitly scoped to the current window. All
* timer firings for a window will be received, but the implementation should choose to ignore
* those that are not applicable.
*
* @param timestamp the time at which the trigger should be re-evaluated
* @param domain the domain that the {@code timestamp} applies to
*/
public abstract void setTimer(Instant timestamp, TimeDomain domain);
/** Create an {@code OnElementContext} for executing the given trigger. */
@Override
public abstract OnElementContext forTrigger(ExecutableTrigger trigger);
}
/**
* Extended {@link TriggerContext} containing information accessible to the {@link #onMerge}
* operational hook.
*/
public abstract class OnMergeContext extends TriggerContext {
/**
* Sets a timer to fire when the watermark or processing time is beyond the given timestamp.
* Timers are not guaranteed to fire immediately, but will be delivered at some time afterwards.
*
* As with {@link #state}, timers are implicitly scoped to the current window. All
* timer firings for a window will be received, but the implementation should choose to ignore
* those that are not applicable.
*
* @param timestamp the time at which the trigger should be re-evaluated
* @param domain the domain that the {@code timestamp} applies to
*/
public abstract void setTimer(Instant timestamp, TimeDomain domain);
/** Create an {@code OnMergeContext} for executing the given trigger. */
@Override
public abstract OnMergeContext forTrigger(ExecutableTrigger trigger);
@Override
public abstract MergingStateAccessor state();
@Override
public abstract MergingTriggerInfo trigger();
}
@Nullable
protected final List> subTriggers;
protected Trigger(@Nullable List> subTriggers) {
this.subTriggers = subTriggers;
}
/**
* Called immediately after an element is first incorporated into a window.
*/
public abstract void onElement(OnElementContext c) throws Exception;
/**
* Called immediately after windows have been merged.
*
* Leaf triggers should update their state by inspecting their status and any state
* in the merging windows. Composite triggers should update their state by calling
* {@link ExecutableTrigger#invokeOnMerge} on their sub-triggers, and applying appropriate logic.
*
*
A trigger such as {@link AfterWatermark#pastEndOfWindow} may no longer be finished;
* it is the responsibility of the trigger itself to record this fact. It is forbidden for
* a trigger to become finished due to {@link #onMerge}, as it has not yet fired the pending
* elements that led to it being ready to fire.
*
*
The implementation does not need to clear out any state associated with the old windows.
*/
public abstract void onMerge(OnMergeContext c) throws Exception;
/**
* Returns {@code true} if the current state of the trigger indicates that its condition
* is satisfied and it is ready to fire.
*/
public abstract boolean shouldFire(TriggerContext context) throws Exception;
/**
* Adjusts the state of the trigger to be ready for the next pane. For example, a
* {@link Repeatedly} trigger will reset its inner trigger, since it has fired.
*
*
If the trigger is finished, it is the responsibility of the trigger itself to
* record that fact via the {@code context}.
*/
public abstract void onFire(TriggerContext context) throws Exception;
/**
* Called to allow the trigger to prefetch any state it will likely need to read from during
* an {@link #onElement} call.
*/
public void prefetchOnElement(StateAccessor state) {
if (subTriggers != null) {
for (Trigger trigger : subTriggers) {
trigger.prefetchOnElement(state);
}
}
}
/**
* Called to allow the trigger to prefetch any state it will likely need to read from during
* an {@link #onMerge} call.
*/
public void prefetchOnMerge(MergingStateAccessor state) {
if (subTriggers != null) {
for (Trigger trigger : subTriggers) {
trigger.prefetchOnMerge(state);
}
}
}
/**
* Called to allow the trigger to prefetch any state it will likely need to read from during
* an {@link #shouldFire} call.
*/
public void prefetchShouldFire(StateAccessor state) {
if (subTriggers != null) {
for (Trigger trigger : subTriggers) {
trigger.prefetchShouldFire(state);
}
}
}
/**
* Called to allow the trigger to prefetch any state it will likely need to read from during
* an {@link #onFire} call.
*/
public void prefetchOnFire(StateAccessor state) {
if (subTriggers != null) {
for (Trigger trigger : subTriggers) {
trigger.prefetchOnFire(state);
}
}
}
/**
* Clear any state associated with this trigger in the given window.
*
* This is called after a trigger has indicated it will never fire again. The trigger system
* keeps enough information to know that the trigger is finished, so this trigger should clear all
* of its state.
*/
public void clear(TriggerContext c) throws Exception {
if (subTriggers != null) {
for (ExecutableTrigger trigger : c.trigger().subTriggers()) {
trigger.invokeClear(c);
}
}
}
public Iterable> subTriggers() {
return subTriggers;
}
/**
* Return a trigger to use after a {@code GroupByKey} to preserve the
* intention of this trigger. Specifically, triggers that are time based
* and intended to provide speculative results should continue providing
* speculative results. Triggers that fire once (or multiple times) should
* continue firing once (or multiple times).
*/
public Trigger getContinuationTrigger() {
if (subTriggers == null) {
return getContinuationTrigger(null);
}
List> subTriggerContinuations = new ArrayList<>();
for (Trigger subTrigger : subTriggers) {
subTriggerContinuations.add(subTrigger.getContinuationTrigger());
}
return getContinuationTrigger(subTriggerContinuations);
}
/**
* Return the {@link #getContinuationTrigger} of this {@code Trigger}. For convenience, this
* is provided the continuation trigger of each of the sub-triggers.
*/
protected abstract Trigger getContinuationTrigger(List> continuationTriggers);
/**
* Returns a bound in watermark time by which this trigger would have fired at least once
* for a given window had there been input data. This is a static property of a trigger
* that does not depend on its state.
*
* For triggers that do not fire based on the watermark advancing, returns
* {@link BoundedWindow#TIMESTAMP_MAX_VALUE}.
*
*
This estimate is used to determine that there are no elements in a side-input window, which
* causes the default value to be used instead.
*/
public abstract Instant getWatermarkThatGuaranteesFiring(W window);
/**
* Returns whether this performs the same triggering as the given {@code Trigger}.
*/
public boolean isCompatible(Trigger other) {
if (!getClass().equals(other.getClass())) {
return false;
}
if (subTriggers == null) {
return other.subTriggers == null;
} else if (other.subTriggers == null) {
return false;
} else if (subTriggers.size() != other.subTriggers.size()) {
return false;
}
for (int i = 0; i < subTriggers.size(); i++) {
if (!subTriggers.get(i).isCompatible(other.subTriggers.get(i))) {
return false;
}
}
return true;
}
@Override
public String toString() {
String simpleName = getClass().getSimpleName();
if (getClass().getEnclosingClass() != null) {
simpleName = getClass().getEnclosingClass().getSimpleName() + "." + simpleName;
}
if (subTriggers == null || subTriggers.size() == 0) {
return simpleName;
} else {
return simpleName + "(" + Joiner.on(", ").join(subTriggers) + ")";
}
}
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (!(obj instanceof Trigger)) {
return false;
}
@SuppressWarnings("unchecked")
Trigger that = (Trigger) obj;
return Objects.equals(getClass(), that.getClass())
&& Objects.equals(subTriggers, that.subTriggers);
}
@Override
public int hashCode() {
return Objects.hash(getClass(), subTriggers);
}
/**
* Specify an ending condition for this trigger. If the {@code until} fires then the combination
* fires.
*
* The expression {@code t1.orFinally(t2)} fires every time {@code t1} fires, and finishes
* as soon as either {@code t1} finishes or {@code t2} fires, in which case it fires one last time
* for {@code t2}. Both {@code t1} and {@code t2} are executed in parallel. This means that
* {@code t1} may have fired since {@code t2} started, so not all of the elements that {@code t2}
* has seen are necessarily in the current pane.
*
*
For example the final firing of the following trigger may only have 1 element:
*
{@code
* Repeatedly.forever(AfterPane.elementCountAtLeast(2))
* .orFinally(AfterPane.elementCountAtLeast(5))
* }
*
* Note that if {@code t1} is {@link OnceTrigger}, then {@code t1.orFinally(t2)} is the same
* as {@code AfterFirst.of(t1, t2)}.
*/
public Trigger orFinally(OnceTrigger until) {
return new OrFinallyTrigger(this, until);
}
@Override
public Trigger buildTrigger() {
return this;
}
/**
* {@link Trigger}s that are guaranteed to fire at most once should extend from this, rather
* than the general {@link Trigger} class to indicate that behavior.
*
* @param {@link BoundedWindow} subclass used to represent the windows used by this
* {@code AtMostOnceTrigger}
*/
public abstract static class OnceTrigger extends Trigger {
protected OnceTrigger(List> subTriggers) {
super(subTriggers);
}
@Override
public final OnceTrigger getContinuationTrigger() {
Trigger continuation = super.getContinuationTrigger();
if (!(continuation instanceof OnceTrigger)) {
throw new IllegalStateException("Continuation of a OnceTrigger must be a OnceTrigger");
}
return (OnceTrigger) continuation;
}
/**
* {@inheritDoc}
*/
@Override
public final void onFire(TriggerContext context) throws Exception {
onOnlyFiring(context);
context.trigger().setFinished(true);
}
/**
* Called exactly once by {@link #onFire} when the trigger is fired. By default,
* invokes {@link #onFire} on all subtriggers for which {@link #shouldFire} is {@code true}.
*/
protected abstract void onOnlyFiring(TriggerContext context) throws Exception;
}
}