/*
* 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.hadoop.chukwa.datacollection.adaptor;
import org.apache.hadoop.chukwa.datacollection.ChunkReceiver;
import org.apache.hadoop.chukwa.datacollection.agent.AdaptorManager;
/**
* An adaptor is a component that runs within the Local Agent, producing chunks
* of monitoring data.
*
* An adaptor can, but need not, have an associated thread. If an adaptor lacks
* a thread, it needs to arrange some mechanism to periodically get control and
* send reports such as a callback somewhere.
*
* Adaptors must be able to stop and resume without losing data, using a byte
* offset in the stream.
*
* If an adaptor crashes at byte offset n, and is restarted at byte offset k,
* with k < n, it is allowed to send different values for bytes k through n the
* second time around. However, the stream must still be parseable, assuming
* that bytes 0-k come from the first run,and bytes k - n come from the second.
*
* Note that Adaptor implements neither equals() nor hashCode(). It is never
* safe to compare two adaptors with equals(). It is safe to use adaptors
* as hash table keys, though two distinct Adaptors will appear as two distinct
* keys. This is the desired behavior, since it means that messages intended
* for one Adaptor will never be received by another, even across Adaptor
* restarts.
*/
public interface Adaptor {
/**
* Start this adaptor
*
* @param type the application type, who is starting this adaptor
* @param status the status string to use for configuration.
* @param offset the stream offset of the first byte sent by this adaptor
* @throws AdaptorException
*/
public void start(String adaptorID, String type, long offset,
ChunkReceiver dest) throws AdaptorException;
/**
* Return the adaptor's state Should not include class name or byte
* offset, which are written by caller. The datatype should, however,
* be written by this method.
*
* @return the adaptor state as a string
*/
public String getCurrentStatus();
public String getType();
/**
* Parse args, return stream name. Do not start running.
*
* Return the stream name, given params.
* The stream name is the part of the Adaptor status that's used to
* determine uniqueness.
*
* @return Stream name as a string, null if params are malformed
*/
public String parseArgs(String datatype, String params, AdaptorManager c);
/**
* Signals this adaptor to come to an orderly stop. The adaptor ought to push
* out all the data it can before exiting depending of the shutdown policy
*
* @return the logical offset at which the adaptor was when the method return
* @throws AdaptorException
*/
public long shutdown(AdaptorShutdownPolicy shutdownPolicy) throws AdaptorException;
/**
* Signals this adaptor to come to an orderly stop. The adaptor ought to push
* out all the data it can before exiting.
*
* This method is synchronous up to 60 seconds
*
* @return the logical offset at which the adaptor stops
* @throws AdaptorException
*/
// @Deprecated
// public long shutdown() throws AdaptorException;
/**
* Signals this adaptor to come to an abrupt stop, as quickly as it can. The
* use case here is "Whups, I didn't mean to start that adaptor tailing a
* gigabyte file, stop it now".
*
* Adaptors might need to do something nontrivial here, e.g., in the case in
* which they have registered periodic timer interrupts, or use a shared
* worker thread from which they need to disengage.
*
* This method is synchronous: In other words, after shutdown() returns, no
* new data should be written.
*
* @throws AdaptorException
*/
// @Deprecated
// public void hardStop() throws AdaptorException;
}