/*
* 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.flink.streaming.api.windowing.triggers;
import java.io.Serializable;
import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.api.common.functions.RuntimeContext;
import org.apache.flink.api.common.state.MergingState;
import org.apache.flink.api.common.state.State;
import org.apache.flink.api.common.state.StateDescriptor;
import org.apache.flink.api.common.state.ValueState;
import org.apache.flink.api.common.typeinfo.TypeInformation;
import org.apache.flink.metrics.MetricGroup;
import org.apache.flink.streaming.api.windowing.windows.Window;
/**
* A {@code Trigger} determines when a pane of a window should be evaluated to emit the
* results for that part of the window.
*
* <p>A pane is the bucket of elements that have the same key (assigned by the
* {@link org.apache.flink.api.java.functions.KeySelector}) and same {@link Window}. An element can
* be in multiple panes of it was assigned to multiple windows by the
* {@link org.apache.flink.streaming.api.windowing.assigners.WindowAssigner}. These panes all
* have their own instance of the {@code Trigger}.
*
* <p>Triggers must not maintain state internally since they can be re-created or reused for
* different keys. All necessary state should be persisted using the state abstraction
* available on the {@link TriggerContext}.
*
* <p>When used with a {@link org.apache.flink.streaming.api.windowing.assigners.MergingWindowAssigner}
* the {@code Trigger} must return {@code true} from {@link #canMerge()} and
* {@link #onMerge(Window, OnMergeContext)} most be properly implemented.
*
* @param <T> The type of elements on which this {@code Trigger} works.
* @param <W> The type of {@link Window Windows} on which this {@code Trigger} can operate.
*/
@PublicEvolving
public abstract class Trigger<T, W extends Window> implements Serializable {
private static final long serialVersionUID = -4104633972991191369L;
/**
* Called for every element that gets added to a pane. The result of this will determine
* whether the pane is evaluated to emit results.
*
* @param element The element that arrived.
* @param timestamp The timestamp of the element that arrived.
* @param window The window to which the element is being added.
* @param ctx A context object that can be used to register timer callbacks.
*/
public abstract TriggerResult onElement(T element, long timestamp, W window, TriggerContext ctx) throws Exception;
/**
* Called when a processing-time timer that was set using the trigger context fires.
*
* @param time The timestamp at which the timer fired.
* @param window The window for which the timer fired.
* @param ctx A context object that can be used to register timer callbacks.
*/
public abstract TriggerResult onProcessingTime(long time, W window, TriggerContext ctx) throws Exception;
/**
* Called when an event-time timer that was set using the trigger context fires.
*
* @param time The timestamp at which the timer fired.
* @param window The window for which the timer fired.
* @param ctx A context object that can be used to register timer callbacks.
*/
public abstract TriggerResult onEventTime(long time, W window, TriggerContext ctx) throws Exception;
/**
* Returns true if this trigger supports merging of trigger state and can therefore
* be used with a
* {@link org.apache.flink.streaming.api.windowing.assigners.MergingWindowAssigner}.
*
* <p>If this returns {@code true} you must properly implement
* {@link #onMerge(Window, OnMergeContext)}
*/
public boolean canMerge() {
return false;
}
/**
* Called when several windows have been merged into one window by the
* {@link org.apache.flink.streaming.api.windowing.assigners.WindowAssigner}.
*
* @param window The new window that results from the merge.
* @param ctx A context object that can be used to register timer callbacks and access state.
*/
public void onMerge(W window, OnMergeContext ctx) throws Exception {
throw new UnsupportedOperationException("This trigger does not support merging.");
}
/**
* Clears any state that the trigger might still hold for the given window. This is called
* when a window is purged. Timers set using {@link TriggerContext#registerEventTimeTimer(long)}
* and {@link TriggerContext#registerProcessingTimeTimer(long)} should be deleted here as
* well as state acquired using {@link TriggerContext#getPartitionedState(StateDescriptor)}.
*/
public abstract void clear(W window, TriggerContext ctx) throws Exception;
// ------------------------------------------------------------------------
/**
* A context object that is given to {@link Trigger} methods to allow them to register timer
* callbacks and deal with state.
*/
public interface TriggerContext {
/**
* Returns the current processing time.
*/
long getCurrentProcessingTime();
/**
* Returns the metric group for this {@link Trigger}. This is the same metric
* group that would be returned from {@link RuntimeContext#getMetricGroup()} in a user
* function.
*
* <p>You must not call methods that create metric objects
* (such as {@link MetricGroup#counter(int)} multiple times but instead call once
* and store the metric object in a field.
*/
MetricGroup getMetricGroup();
/**
* Returns the current watermark time.
*/
long getCurrentWatermark();
/**
* Register a system time callback. When the current system time passes the specified
* time {@link Trigger#onProcessingTime(long, Window, TriggerContext)} is called with the time specified here.
*
* @param time The time at which to invoke {@link Trigger#onProcessingTime(long, Window, TriggerContext)}
*/
void registerProcessingTimeTimer(long time);
/**
* Register an event-time callback. When the current watermark passes the specified
* time {@link Trigger#onEventTime(long, Window, TriggerContext)} is called with the time specified here.
*
* @param time The watermark at which to invoke {@link Trigger#onEventTime(long, Window, TriggerContext)}
* @see org.apache.flink.streaming.api.watermark.Watermark
*/
void registerEventTimeTimer(long time);
/**
* Delete the processing time trigger for the given time.
*/
void deleteProcessingTimeTimer(long time);
/**
* Delete the event-time trigger for the given time.
*/
void deleteEventTimeTimer(long time);
/**
* Retrieves a {@link State} object that can be used to interact with
* fault-tolerant state that is scoped to the window and key of the current
* trigger invocation.
*
* @param stateDescriptor The StateDescriptor that contains the name and type of the
* state that is being accessed.
* @param <S> The type of the state.
* @return The partitioned state object.
* @throws UnsupportedOperationException Thrown, if no partitioned state is available for the
* function (function is not part os a KeyedStream).
*/
<S extends State> S getPartitionedState(StateDescriptor<S, ?> stateDescriptor);
/**
* Retrieves a {@link ValueState} object that can be used to interact with
* fault-tolerant state that is scoped to the window and key of the current
* trigger invocation.
*
* @param name The name of the key/value state.
* @param stateType The class of the type that is stored in the state. Used to generate
* serializers for managed memory and checkpointing.
* @param defaultState The default state value, returned when the state is accessed and
* no value has yet been set for the key. May be null.
*
* @param <S> The type of the state.
* @return The partitioned state object.
* @throws UnsupportedOperationException Thrown, if no partitioned state is available for the
* function (function is not part os a KeyedStream).
* @deprecated Use {@link #getPartitionedState(StateDescriptor)}.
*/
@Deprecated
<S extends Serializable> ValueState<S> getKeyValueState(String name, Class<S> stateType, S defaultState);
/**
* Retrieves a {@link ValueState} object that can be used to interact with
* fault-tolerant state that is scoped to the window and key of the current
* trigger invocation.
*
* @param name The name of the key/value state.
* @param stateType The type information for the type that is stored in the state.
* Used to create serializers for managed memory and checkpoints.
* @param defaultState The default state value, returned when the state is accessed and
* no value has yet been set for the key. May be null.
*
* @param <S> The type of the state.
* @return The partitioned state object.
* @throws UnsupportedOperationException Thrown, if no partitioned state is available for the
* function (function is not part os a KeyedStream).
* @deprecated Use {@link #getPartitionedState(StateDescriptor)}.
*/
@Deprecated
<S extends Serializable> ValueState<S> getKeyValueState(String name, TypeInformation<S> stateType, S defaultState);
}
/**
* Extension of {@link TriggerContext} that is given to
* {@link Trigger#onMerge(Window, OnMergeContext)}.
*/
public interface OnMergeContext extends TriggerContext {
<S extends MergingState<?, ?>> void mergePartitionedState(StateDescriptor<S, ?> stateDescriptor);
}
}