| /** |
| * 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 |
| } |
| } |