storm-client/src/jvm/org/apache/storm/windowing/TriggerPolicy.java

/**
 * 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;

/**
 * Triggers the window calculations based on the policy.
 *
 * @param <T> the type of the event that is tracked
 */
public interface TriggerPolicy<T, S> {
    /**
     * Tracks the event and could use this to invoke the trigger.
     *
     * @param event the input event
     */
    void track(Event<T> event);

    /**
     * resets the trigger policy.
     */
    void reset();

    /**
     * Starts the trigger policy. This can be used during recovery to start the triggers after recovery is complete.
     */
    void start();

    /**
     * Any clean up could be handled here.
     */
    void shutdown();

    /**
     * Return runtime state to be checkpointed by the framework for restoring the trigger policy in case of failures.
     *
     * @return the state
     */
    S getState();

    /**
     * Restore the trigger policy from the state that was earlier checkpointed by the framework.
     *
     * @param state the state
     */
    void restoreState(S state);
}