| // Copyright 2017 Twitter. All rights reserved. |
| // |
| // 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.twitter.heron.api.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> { |
| /** |
| * 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 |
| } |
| |
| /** |
| * 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 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); |
| |
| /** |
| * 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); |
| |
| /** |
| * Returns the current context that is part of this eviction policy. |
| * |
| * @return the eviction context |
| */ |
| EvictionContext getContext(); |
| |
| /** |
| * Resets the eviction policy. |
| */ |
| void reset(); |
| } |