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/**
*
* 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.classification.InterfaceAudience;
import org.apache.hadoop.hbase.Server;
import org.apache.htrace.Span;
import org.apache.htrace.Trace;
import org.apache.htrace.TraceScope;
/**
* Abstract base class for all HBase event handlers. Subclasses should
* implement the {@link #process()} and {@link #prepare()} methods. Subclasses
* should also do all necessary checks up in their prepare() 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.
*
* 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 ExecutorService, has a switch for passing
* event type to executor.
*
* 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
*/
@InterfaceAudience.Private
public abstract class EventHandler implements Runnable, Comparable {
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 final 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;
// Time to wait for events to happen, should be kept short
protected int waitingTimeForEvents;
private final Span parent;
/**
* 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.
*/
void beforeProcess(EventHandler event);
/**
* Called after any event is processed
* @param event The event handler whose process method is about to be called.
*/
void afterProcess(EventHandler event);
}
/**
* Default base class constructor.
*/
public EventHandler(Server server, EventType eventType) {
this.parent = Trace.currentSpan();
this.server = server;
this.eventType = eventType;
seqid = seqids.incrementAndGet();
if (server != null) {
this.waitingTimeForEvents = server.getConfiguration().
getInt("hbase.master.event.waiting.time", 1000);
}
}
/**
* Event handlers should do all the necessary checks in this method (rather than
* in the constructor, or in process()) so that the caller, which is mostly executed
* in the ipc context can fail fast. Process is executed async from the client ipc,
* so this method gives a quick chance to do some basic checks.
* Should be called after constructing the EventHandler, and before process().
* @return the instance of this class
* @throws Exception when something goes wrong
*/
public EventHandler prepare() throws Exception {
return this;
}
@Override
public void run() {
TraceScope chunk = Trace.startSpan(this.getClass().getSimpleName(), parent);
try {
if (getListener() != null) getListener().beforeProcess(this);
process();
if (getListener() != null) getListener().afterProcess(this);
} catch(Throwable t) {
handleException(t);
} finally {
chunk.close();
}
}
/**
* 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.
*
* Lowest priority is Integer.MAX_VALUE. Highest priority is 0.
*
* Subclasses should override this method to allow prioritizing handlers.
*
* Handlers with the same priority are handled in FIFO order.
*
* @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.
*
* 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;
}
@Override
public String toString() {
return "Event #" + getSeqid() +
" of type " + eventType +
" (" + getInformativeName() + ")";
}
/**
* Event implementations should override thie class to provide an
* informative name about what event they are handling. For example,
* event-specific information such as which region or server is
* being processed should be included if possible.
*/
public String getInformativeName() {
return this.getClass().toString();
}
/**
* Event exception handler, may be overridden
* @param t Throwable object
*/
protected void handleException(Throwable t) {
String msg = "Caught throwable while processing event " + eventType;
LOG.error(msg, t);
if (server != null && (t instanceof Error || t instanceof RuntimeException)) {
server.abort(msg, t);
}
}
}