All Downloads are FREE. Search and download functionalities are using the official Maven repository.

org.apache.hadoop.hbase.executor.EventHandler Maven / Gradle / Ivy

There is a newer version: 3.0.0-beta-1
Show newest version
/**
 *
 * 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.hadoop.hbase.Server;
import org.apache.hadoop.hbase.trace.TraceUtil;
import org.apache.htrace.core.Span;
import org.apache.htrace.core.TraceScope;
import org.apache.htrace.core.Tracer;
import org.apache.yetus.audience.InterfaceAudience;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * 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. *

* @see ExecutorService */ @InterfaceAudience.Private public abstract class EventHandler implements Runnable, Comparable { private static final Logger LOG = LoggerFactory.getLogger(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; // Time to wait for events to happen, should be kept short protected int waitingTimeForEvents; private final Span parent; /** * Default base class constructor. */ public EventHandler(Server server, EventType eventType) { this.parent = Tracer.getCurrentSpan(); 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() { try (TraceScope scope = TraceUtil.createTrace(this.getClass().getSimpleName(), parent)) { process(); } catch(Throwable t) { handleException(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. *

* 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; } @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); } } }





© 2015 - 2024 Weber Informatics LLC | Privacy Policy