/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.beam.runners.core.triggers;
import org.apache.beam.runners.core.triggers.TriggerStateMachine.OnceTriggerStateMachine;
import org.apache.beam.sdk.transforms.GroupByKey;
import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
/**
* A {@link TriggerStateMachine} which never fires.
*
* <p>Using this trigger will only produce output when the watermark passes the end of the
* {@link BoundedWindow window} plus the allowed lateness.
*/
public final class NeverStateMachine extends OnceTriggerStateMachine {
/**
* Returns a trigger which never fires. Output will be produced from the using {@link GroupByKey}
* when the {@link BoundedWindow} closes.
*/
public static NeverStateMachine ever() {
// NeverTrigger ignores all inputs and is Window-type independent.
return new NeverStateMachine();
}
private NeverStateMachine() {
super(null);
}
@Override
public void onElement(OnElementContext c) {}
@Override
public void onMerge(OnMergeContext c) {}
@Override
public boolean shouldFire(TriggerStateMachine.TriggerContext context) {
return false;
}
@Override
protected void onOnlyFiring(TriggerStateMachine.TriggerContext context) {
throw new UnsupportedOperationException(
String.format("%s should never fire", getClass().getSimpleName()));
}
}