/
EvictionPolicy.java
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/
EvictionPolicy.java
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/**
* 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.storm.windowing;
/**
* Eviction policy tracks events and decides whether an event should be evicted from the window or not.
*
* @param <T> the type of event that is tracked.
*/
public interface EvictionPolicy<T, S> {
/**
* Decides if an event should be expired from the window, processed in the current window or kept for later processing.
*
* @param event the input event
* @return the {@link org.apache.storm.windowing.EvictionPolicy.Action} to be taken based on the input event
*/
Action evict(Event<T> event);
/**
* Tracks the event to later decide whether {@link EvictionPolicy#evict(Event)} should evict it or not.
*
* @param event the input event to be tracked
*/
void track(Event<T> event);
/**
* Returns the current context that is part of this eviction policy.
*
* @return the eviction context
*/
EvictionContext getContext();
/**
* Sets a context in the eviction policy that can be used while evicting the events. E.g. For TimeEvictionPolicy, this could be used to
* set the reference timestamp.
*
* @param context the eviction context
*/
void setContext(EvictionContext context);
/**
* Resets the eviction policy.
*/
void reset();
/**
* Return runtime state to be checkpointed by the framework for restoring the eviction policy in case of failures.
*
* @return the state
*/
S getState();
/**
* Restore the eviction policy from the state that was earlier checkpointed by the framework.
*
* @param state the state
*/
void restoreState(S state);
/**
* The action to be taken when {@link EvictionPolicy#evict(Event)} is invoked.
*/
enum Action {
/**
* expire the event and remove it from the queue.
*/
EXPIRE,
/**
* process the event in the current window of events.
*/
PROCESS,
/**
* don't include in the current window but keep the event in the queue for evaluating as a part of future windows.
*/
KEEP,
/**
* stop processing the queue, there cannot be anymore events satisfying the eviction policy.
*/
STOP
}
}