/**
* Copyright 2010 The Apache Software Foundation
*
* 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.hbase.executor;
import java.io.IOException;
import java.util.concurrent.atomic.AtomicLong;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hbase.Server;
/**
* Abstract base class for all HBase event handlers. Subclasses should
* implement the {@link #process()} method. Subclasses should also do all
* necessary checks up in their constructor if possible -- check table exists,
* is disabled, etc. -- so they fail fast rather than later when process is
* running. Do it this way because process be invoked directly but event
* handlers are also
* run in an executor context -- i.e. asynchronously -- and in this case,
* exceptions thrown at process time will not be seen by the invoker, not till
* we implement a call-back mechanism so the client can pick them up later.
* <p>
* Event handlers have an {@link EventType}.
* {@link EventType} is a list of ALL handler event types. We need to keep
* a full list in one place -- and as enums is a good shorthand for an
* implemenations -- because event handlers can be passed to executors when
* they are to be run asynchronously. The
* hbase executor, see {@link ExecutorService}, has a switch for passing
* event type to executor.
* <p>
* Event listeners can be installed and will be called pre- and post- process if
* this EventHandler is run in a Thread (its a Runnable so if its {@link #run()}
* method gets called). Implement
* {@link EventHandlerListener}s, and registering using
* {@link #setListener(EventHandlerListener)}.
* @see ExecutorService
*/
public abstract class EventHandler implements Runnable, Comparable<Runnable> {
private static final Log LOG = LogFactory.getLog(EventHandler.class);
// type of event this object represents
protected EventType eventType;
protected Server server;
// sequence id generator for default FIFO ordering of events
protected static AtomicLong seqids = new AtomicLong(0);
// sequence id for this event
private final long seqid;
// Listener to call pre- and post- processing. May be null.
private EventHandlerListener listener;
/**
* This interface provides pre- and post-process hooks for events.
*/
public interface EventHandlerListener {
/**
* Called before any event is processed
* @param event The event handler whose process method is about to be called.
*/
public void beforeProcess(EventHandler event);
/**
* Called after any event is processed
* @param event The event handler whose process method is about to be called.
*/
public void afterProcess(EventHandler event);
}
/**
* List of all HBase event handler types. Event types are named by a
* convention: event type names specify the component from which the event
* originated and then where its destined -- e.g. RS2ZK_ prefix means the
* event came from a regionserver destined for zookeeper -- and then what
* the even is; e.g. REGION_OPENING.
*
* <p>We give the enums indices so we can add types later and keep them
* grouped together rather than have to add them always to the end as we
* would have to if we used raw enum ordinals.
*/
public enum EventType {
// Messages originating from RS (NOTE: there is NO direct communication from
// RS to Master). These are a result of RS updates into ZK.
RS_ZK_REGION_CLOSING (1), // RS is in process of closing a region
RS_ZK_REGION_CLOSED (2), // RS has finished closing a region
RS_ZK_REGION_OPENING (3), // RS is in process of opening a region
RS_ZK_REGION_OPENED (4), // RS has finished opening a region
// Messages originating from Master to RS
M_RS_OPEN_REGION (20), // Master asking RS to open a region
M_RS_OPEN_ROOT (21), // Master asking RS to open root
M_RS_OPEN_META (22), // Master asking RS to open meta
M_RS_CLOSE_REGION (23), // Master asking RS to close a region
M_RS_CLOSE_ROOT (24), // Master asking RS to close root
M_RS_CLOSE_META (25), // Master asking RS to close meta
// Messages originating from Client to Master
C_M_DELETE_TABLE (40), // Client asking Master to delete a table
C_M_DISABLE_TABLE (41), // Client asking Master to disable a table
C_M_ENABLE_TABLE (42), // Client asking Master to enable a table
C_M_MODIFY_TABLE (43), // Client asking Master to modify a table
C_M_ADD_FAMILY (44), // Client asking Master to add family to table
C_M_DELETE_FAMILY (45), // Client asking Master to delete family of table
C_M_MODIFY_FAMILY (46), // Client asking Master to modify family of table
// Updates from master to ZK. This is done by the master and there is
// nothing to process by either Master or RS
M_ZK_REGION_OFFLINE (50), // Master adds this region as offline in ZK
// Master controlled events to be executed on the master
M_SERVER_SHUTDOWN (70), // Master is processing shutdown of a RS
M_META_SERVER_SHUTDOWN (72); // Master is processing shutdown of RS hosting a meta region (-ROOT- or .META.).
/**
* Constructor
*/
EventType(int value) {}
}
/**
* Default base class constructor.
*/
public EventHandler(Server server, EventType eventType) {
this.server = server;
this.eventType = eventType;
seqid = seqids.incrementAndGet();
}
public void run() {
try {
if (getListener() != null) getListener().beforeProcess(this);
process();
if (getListener() != null) getListener().afterProcess(this);
} catch(Throwable t) {
LOG.error("Caught throwable while processing event " + eventType, t);
}
}
/**
* This method is the main processing loop to be implemented by the various
* subclasses.
* @throws IOException
*/
public abstract void process() throws IOException;
/**
* Return the event type
* @return The event type.
*/
public EventType getEventType() {
return this.eventType;
}
/**
* Get the priority level for this handler instance. This uses natural
* ordering so lower numbers are higher priority.
* <p>
* Lowest priority is Integer.MAX_VALUE. Highest priority is 0.
* <p>
* Subclasses should override this method to allow prioritizing handlers.
* <p>
* Handlers with the same priority are handled in FIFO order.
* <p>
* @return Integer.MAX_VALUE by default, override to set higher priorities
*/
public int getPriority() {
return Integer.MAX_VALUE;
}
/**
* @return This events' sequence id.
*/
public long getSeqid() {
return this.seqid;
}
/**
* Default prioritized runnable comparator which implements a FIFO ordering.
* <p>
* Subclasses should not override this. Instead, if they want to implement
* priority beyond FIFO, they should override {@link #getPriority()}.
*/
@Override
public int compareTo(Runnable o) {
EventHandler eh = (EventHandler)o;
if(getPriority() != eh.getPriority()) {
return (getPriority() < eh.getPriority()) ? -1 : 1;
}
return (this.seqid < eh.seqid) ? -1 : 1;
}
/**
* @return Current listener or null if none set.
*/
public synchronized EventHandlerListener getListener() {
return listener;
}
/**
* @param listener Listener to call pre- and post- {@link #process()}.
*/
public synchronized void setListener(EventHandlerListener listener) {
this.listener = listener;
}
}